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20110830

Radiology signs- A


A

Accordion sign 
Appearance of bowel that may be seen with pseudomembranous colitis.

Marked submucosal edema (arrows) is present in the right colon. Oral contrast material (arrowhead) is trapped within the lumen

Air crescent sign 
  Figure 1b.
 On healing, interval development of at least two air crescent signs (arrowheads), which coincided with recovery of the patient’s white blood cell count.
Appearance of cavitation that may be seen with invasive apergillosis.
Anteater's nose sign 


Sign of calcaneonavicular tarsal coalition.
Apple Core lesion 


Circumferential narrowing of the lumen secondary to colon cancer.

20110826

Acroosteolysis

PINCH FO: Mnemonic for Etiologies of Acroosteolysis

PINCH FO

Psoriasis
Pyknodysostosis
Injury (thermal burn, frost bite)
Neuropathy
Diabetes
Leprosy

Collagen vascular disease
Scleroderma
Raynaud's disease

Hyperparathyroidism
Familial (Hadju-Cheney syndrome)
Other
Polyvinyl chloride exposure
Progeria

Imaging Findings:
Primary-hyperparathyroidism-002.jpg

Acroosteolysis is characterized by bone resorption in the fingers and toes.
Radiographs show terminal phalangeal resorption in the fingers and toes.


Hemostatic Disorders and Coagulation Test Abnormalities


Prolonged activated partial thromboplastin time (aPTT)

  No clinical bleeding – factors XII, high-molecular-weight kininogen, protein kinase
  Variable, but usually mild, bleeding – factor XI, mild FVIII and FIX
  Frequent, severe bleeding – severe deficiencies of FVIII and FIX
  Heparin


Prolonged prothrombin time (PT)

  Factor VII deficiency
  Vitamin K deficiency – early
  Warfarin anticoagulation


Prolonged aPTT and PT

  Factor II, V or X deficiency
  Vitamin K deficiency – late
  Direct thrombin inhibitors


Prolonged thrombin time

  Heparin or heparin-like inhibitors
  Mild or no bleeding – dysfibrinogenemia
  Frequent, severe bleeding – afibrinogenemia


Prolonged PT and/or aPTT not correct with mixing with normal plasma

  Bleeding – specific factor inhibitor
  No symptoms, or clotting and/or pregnancy loss – lupus anticoagulant
  Disseminated intravascular coagulation
  Heparin or direct thrombin inhibitor


Abnormal clot solubility

  Factor XIII deficiency
  Inhibitors or defective cross-linking


Rapid clot lysis

  Deficiency of 2-antiplasmin or plasminogen activator inhibitor 1
  Treatment with fibrinolytic therapy

Primary Hemostatic (Platelet Plug) Disorders


Defects of Platelet Adhesion


  von Willebrand disease
  Bernard-Soulier syndrome (absence of dysfunction of GpIb-IX-V)


Defects of Platelet Aggregation


  Glanzmann's thrombasthenia (absence or dysfunction of GpIIbIIIa)
  Afibrinogenemia


Defects of Platelet Secretion


  Decreased cyclooxygenase activity
    Drug-induced (aspirin, nonsteroidal anti-inflammatory agents)
    Inherited
  Granule storage pool defects
    Inherited
    Acquired
  Nonspecific drug effects
  Uremia
  Platelet coating (e.g., paraprotein, penicillin)


Defect of platelet coagulant activity
  Scott's syndrome

Scott syndrome is a rare congenital bleeding disorder that is due to a defect in a platelet mechanism required for blood coagulation.When normal platelets are activated, as may occur at sites of vascular injury, phosphatidylserine (PS) in the inner leaflet of the platelet membrane is transported to the outer membrane surface of the platelet, where it provides a binding site for plasma protein complexes, such as factor VIIIa-IXa (tenase) and factor Va-Xa (prothrombinase), that are involved in the conversion of prothrombin to thrombin.


In Scott syndrome, the mechanism for translocating PS to the platelet membrane is defective, resulting in impaired thrombinformation. A similar defect in PS translocation has also been demonstrated in Scott syndrome red blood cells and Epstein-Barr virus transformed lymphocytes, suggesting that the defect in Scott syndrome reflects a mutation in a stem cell that effects multiple hematological lineages. The basis for the defect in PS translocation is, at present, unknown. A candidate protein, scramblase, that may be involved in this process appears to be normal in Scott syndrome platelets.Other possible defects in PS translocation, reported in some patients, require further study. The initially reported patient with Scott Syndrome has been found to have a mutation at a splice-acceptor site of the gene encoding transmembrane protein 16F (TMEM16F)[9]. At present, the only treatment for episodes of bleeding is the transfusion of normal platelets.

Platelet Adhesion and Aggregation - YouTube

Platelet Adhesion and Aggregation - YouTube: "http://youtu.be/0pnpoEy0eYE"

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20110825

Linkage and Association Studies

There are two primary strategies for mapping genes that cause or increase susceptibility to human disease:
(1) classic linkage can be performed based on a known genetic model or, when the model is unknown, by studying pairs of affected relatives.
(2) disease genes can be mapped using allelic association studies.

Genetic Linkage


Genetic linkage refers to the fact that genes are physically connected, or linked, to one another along the chromosomes.

Two fundamental principles are essential for understanding the concept of linkage:

(1) when two genes are close together on a chromosome, they are usually transmitted together, unless a recombination event separates them.
(2) the odds of a crossover, or recombination event, between two linked genes is proportional to the distance that separates them. Thus, genes that are further apart are more likely to undergo a recombination event than genes that are very close together.

The detection of chromosomal loci that segregate with a disease by linkage can be used to identify the gene responsible for the disease (positional cloning) and to predict the odds of disease gene transmission in genetic counseling.

Polymorphisms are essential for linkage studies because they provide a means to distinguish the maternal and paternal chromosomes in an individual. On average, 1 out of every 1000 bp varies from one person to the next. Although this degree of variation seems low (99.9% identical), it means that >3 million sequence differences exist between any two unrelated individuals and the probability that the sequence at such loci will differ on the two homologous chromosomes is high (often >70–90%). These sequence variations include VNTRs, short tandem repeats (STRs), and SNPs. Most STRs, also called polymorphic microsatellite markers, consist of di-, tri-, or tetranucleotide repeats that can be measured readily using PCR. Characterization of SNPs, using DNA chips, provides an important new tool for comprehensive analyses of genetic variation, linkage, and association studies. Although these sequence variations usually have no apparent functional consequences, they provide much of the basis for variation in genetic traits.

In order to identify a chromosomal locus that segregates with a disease, it is necessary to characterize polymorphic DNA markers from affected and unaffected individuals of one or several pedigrees. One can then assess whether certain marker alleles cosegregate with the disease.

Markers that are closest to the disease gene are less likely to undergo recombination events and therefore receive a higher linkage score.
Linkage is expressed as a lod (logarithm of odds) score—the ratio of the probability that the disease and marker loci are linked rather than unlinked. Lod scores of +3 (1000:1) are generally accepted as supporting linkage, whereas a score of –2 is consistent with the absence of linkage.


Allelic association refers to a situation in which the frequency of an allele is significantly increased or decreased in individuals affected by a particular disease in comparison to controls.

Linkage and association differ in several aspects. Genetic linkage is demonstrable in families or sibships. Association studies, on the other hand, compare a population of affected individuals with a control population. Association studies can be performed as case-control studies that include unrelated affected individuals and matched controls, or as family-based studies that compare the frequencies of alleles transmitted or not transmitted to affected children. Allelic association studies are particularly useful for identifying susceptibility genes in complex diseases.

When alleles at two loci occur more frequently in combination than would be predicted (based on known allele frequencies and recombination fractions), they are said to be in linkage disequilibrium .

Nucleotide Repeat Expansion Disorders


Several diseases are associated with an increase in the number of nucleotide repeats above a certain threshold . The repeats are sometimes located within the coding region of the genes, as in Huntington disease or the X-linked form of spinal and bulbar muscular atrophy (SBMA, Kennedy syndrome). In other instances, the repeats probably alter gene regulatory sequences.

If an expansion is present, the DNA fragment is unstable and tends to expand further during cell division. The length of the nucleotide repeat often correlates with the severity of the disease. When repeat length increases from one generation to the next, disease manifestations may worsen or be observed at an earlier age; this phenomenon is referred to as anticipation. In Huntington disease, for example, there is a correlation between age of onset and length of the triplet codon expansion. Anticipation has also been documented in other diseases caused by dynamic mutations in trinucleotide repeats . The repeat number may also vary in a tissue-specific manner. In myotonic dystrophy, the CTG repeat may be tenfold greater in muscle tissue than in lymphocytes .

Selected Trinucleotide Repeat Disorders

X-chromosomal spinobulbar muscular atrophy (SBMA)
Xq11-q12
CAG
XR
Androgen receptor

Fragile X-syndrome (FRAXA)         Fragile X-syndrome (FRAXE)
CGG                                                GCC
XR                                                   XR
FMR-1 protein                                 FMR-2 protein


Dystrophia myotonica (DM)
CTG
AD, variable penetrance
Myotonin protein kinase

Huntington disease (HD)
CAG
AD
Huntingtin

Spinocerebellar ataxia type 1 (SCA1)
CAG
AD
Ataxin 1

Spinocerebellar ataxia type 2 (SCA2)
CAG
AD
Ataxin 2

Spinocerebellar ataxia type 3 (SCA3); Machado Joseph disease (MD)
CAG
AD
Ataxin 3

Spinocerebellar ataxia type 6 (SCA6, CACNAIA)
CAG
AD
Alpha 1A voltage-dependent L-type calcium channel

Spinocerebellar ataxia type 7 (SCA7)
CAG
AD
Ataxin 7

Spinocerebellar ataxia type 12 (SCA12)
CAG
AD
Protein phosphatase 2A

Dentorubral pallidoluysiane atrophy (DRPLA)
CAG
AD
Atrophin 1

Friedreich ataxia (FRDA1)
GAA
AR
Frataxin

X-inactivation, Imprinting, and Uniparental Disomy


According to traditional Mendelian principles, the parental origin of a mutant gene is irrelevant for the expression of the phenotype. There are, however, important exceptions to this rule.

 X-inactivation prevents the expression of most genes on one of the two X-chromosomes in every cell of a female.
Gene inactivation also occurs on selected chromosomal regions of autosomes. This phenomenon, referred to as genomic imprinting, leads to inheritable preferential expression of one of the parental alleles. It is of pathophysiologic importance in disorders where the transmission of disease is dependent on the sex of the transmitting parent and, thus, plays an important role in the expression of certain genetic disorders. Two classic examples are the Prader-Willi syndrome and Angelman syndrome .

Prader-Willi syndrome is characterized by diminished fetal activity, obesity, hypotonia, mental retardation, short stature, and hypogonadotropic hypogonadism. Deletions of the paternal copy of the Prader-Willi locus located on the short arm of chromosome 15 result in a contiguous gene syndrome involving missing paternal copies of the necdin and SNRPN genes, among others. In contrast, patients with Angelman syndrome, characterized by mental retardation, seizures, ataxia, and hypotonia, have deletions involving the maternal copy of this region on chromosome 15. These two syndromes may also result from uniparental disomy. In this case, the syndromes are not caused by deletions on chromosome 15 but by the inheritance of either two maternal chromosomes (Prader-Willi syndrome) or two paternal chromosomes (Angelman syndrome).

Genomic imprinting, or uniparental disomy, is involved in the pathogenesis of several other disorders and malignancies. For example, hydatidiform moles contain a normal number of diploid chromosomes, but they are all of paternal origin. The opposite situation occurs in ovarian teratomata, with 46 chromosomes of maternal origin.

Expression of the imprinted gene for insulin-like growth factor II (IGF-II) is involved in the pathogenesis of the cancer-predisposing Beckwith-Wiedemann syndrome (BWS). These children show somatic overgrowth with organomegalies and hemihypertrophy, and they have an increased risk of embryonal malignancies such as Wilm's tumor. Normally, only the paternally derived copy of the IGF-II gene is active and the maternal copy is inactive. Imprinting of the IGF-II gene is regulated by H19, which encodes an RNA transcript that is not translated into protein. Disruption or lack of H19 methylation leads to a relaxation of IGF-II imprinting and expression of both alleles.

Meiotically and mitotically heritable changes in gene expression not associated with DNA sequence alterations are referred to as epigenetic effects. These changes involve DNA methylation, histone modifications, and RNA-mediated silencing, resulting in gene repression without a change in the coding sequence. Epigenetic alterations are increasingly recognized to play a role in human diseases such as cancer, mental retardation, hematologic disorders, and possibly in aging. For example, de novo methylation of CpG islands, regions of >500 bp in size with a GC content >55% in promoter regions that are normally unmethylated, is a hallmark of human cancers. Inhibitors of enzymes controlling epigenetic modifications such as histone deacetylases and DNA methyltransferases reverse gene silencing and represent a promising new group of antineoplastic agents.

Mosaicism


Mosaicism refers to the presence of two or more genetically distinct cell lines in the tissues of an individual. It results from a mutation that occurs during embryonic, fetal, or extrauterine development.

The developmental stage at which the mutation arises will determine whether germ cells and/or somatic cells are involved.

Chromosomal mosaicism results from non-disjunction at an early embryonic mitotic division, leading to the persistence of more than one cell line, as exemplified by some patients with Turner syndrome .

Somatic mosaicism is characterized by a patchy distribution of genetically altered somatic cells. The McCune-Albright syndrome, for example, is caused by activating mutations in the stimulatory G protein (Gs-alpha) that occur early in development . The clinical phenotype varies depending on the tissue distribution of the mutation; manifestations include ovarian cysts that secrete sex steroids and cause precocious puberty, polyostotic fibrous dysplasia, cafĂ©-au-lait skin pigmentation, growth hormone–secreting pituitary adenomas, and hypersecreting autonomous thyroid nodules.

Mitochondrial Disorders


Mendelian inheritance refers to the transmission of genes encoded by DNA contained in the nuclear chromosomes. In addition, each mitochondrion contains several copies of a small circular chromosome. The mitochondrial DNA (mtDNA) is ~16.5 kb and encodes transfer and ribosomal RNAs and 13 proteins that are components of the respiratory chain involved in oxidative phosphorylation and ATP generation.

The mitochondrial genome does not recombine and is inherited through the maternal line because sperm does not contribute significant cytoplasmic components to the zygote. A noncoding region of the mitochondrial chromosome, referred to as D-loop, is highly polymorphic. This property, together with the absence of mtDNA recombination, makes it a valuable tool for studies tracing human migration and evolution, and it is also used for specific forensic applications.

Inherited mitochondrial disorders are transmitted in a matrilineal fashion; all children from an affected mother will inherit the disease, but it will not be transmitted from an affected father to his children . Alterations in the mtDNA affecting enzymes required for oxidative phosphorylation lead to reduction of ATP supply, generation of free radicals, and induction of apoptosis.

 Several syndromic disorders arising from mutations in the mitochondrial genome are known in humans and they affect both protein-coding and tRNA genes . The broad clinical spectrum often involves (cardio)myopathies and encephalopathies because of the high dependence of these tissues on oxidative phosphorylation. The age of onset and the clinical course are highly variable because of the unusual mechanisms of mtDNA transmission, which replicates independently from nuclear DNA.

During cell replication, the proportion of wild-type and mutant mitochondria can drift among different cells and tissues. The resulting heterogeneity in the proportion of mitochondria with and without a mutation is referred to as heteroplasmia and underlies the phenotypic variability that is characteristic of mitochondrial diseases.

Selected Mitochondrial Diseases

1. MELAS syndrome: mitochondrial myopathy with encephalopathy, lactacidosis, and stroke

2. Leber's optic atrophy: hereditary optical neuropathy

3. Kearns-Sayre syndrome (KSS): ophthalmoplegia, pigmental degeneration of the retina, cardiomyopathy

4. MERRF syndrome: myoclonic epilepsy and ragged-red fibers

5. Neurogenic muscular weakness with ataxia and retinitis pigmentosa (NARP)

6. Progressive external ophthalmoplegia (CEOP)

7. Pearson syndrome (PEAR): bone marrow and pancreatic failure

8. Autosomal dominant inherited mitochondrial myopathy with mitochondrial deletion (ADMIMY)

9. Somatic mutations in cytochrome b gene: exercise intolerance, lactic acidosis, complex III deficiency, muscle pain, ragged-red fibers


Acquired somatic mutations in mitochondria are thought to be involved in several age-dependent degenerative disorders affecting predominantly muscle and the peripheral and central nervous system (e.g., Alzheimer's and Parkinson's disease). Establishing that a mtDNA alteration is causal for a clinical phenotype is challenging because of the high degree of polymorphism in mtDNA and the phenotypic variability characteristic of these disorders. Certain pharmacologic treatments may have an impact on mitochondria and/or their function. For example, treatment with the antiretroviral compound azidothymidine (AZT) causes an acquired mitochondrial myopathy through depletion of muscular mtDNA.

20110824

von Willebrand Disease


vWD is the most common inherited bleeding disorder.

vWF serves two roles:

(1) as the major adhesion molecule that tethers the platelet to the exposed subendothelium

(2) as the binding protein for FVIII, resulting in significant prolongation of the FVIII half-life in circulation.

 The platelet-adhesive function of vWF is critically dependent on the presence of large vWF multimers, while FVIII binding is not. Most of the symptoms of vWD are "platelet-like" except in more severe vWD when the FVIII is low enough to produce symptoms similar to those found in Factor VIII deficiency (hemophilia A).

vWD has been classified into three major types, with four subtypes of type 2. By far the most common type of vWD is type 1 disease, with a parallel decrease in vWF protein, vWF function, and FVIII levels, accounting for at least 80% of cases. Patients have predominantly mucosal bleeding symptoms, although postoperative bleeding can also be seen. Bleeding symptoms are very uncommon in infancy and usually manifest later in childhood with excessive bruising and epistaxis. Since these symptoms occur commonly in childhood, the clinician should particularly note bruising at sites unlikely to be traumatized and/or prolonged epistaxis requiring medical attention. Menorrhagia is a common manifestation of vWD. Menstrual bleeding resulting in anemia should warrant an evaluation for vWD and, if negative, functional platelet disorders. Frequently, mild type 1 vWD first manifests with dental extractions, particularly wisdom tooth extraction, or tonsillectomy.



Not all patients with low vWF levels have bleeding symptoms. Whether patients bleed or not will depend on the overall hemostatic balance they have inherited, along with environmental influences and the type of hemostatic challenges they experience. Although the inheritance of vWD is autosomal, many factors influence both vWF levels and bleeding symptoms. These have not all been defined but include blood type, thyroid hormone status, race, stress, exercise, and hormonal (both endogenous and exogenous) influences. Patients with type O blood have vWF protein levels about one-half those of patients with AB blood type; in fact, the normal range for patients with type O blood overlaps that usually considered diagnostic for vWD. A mildly decreased vWF level should perhaps be viewed more as a risk factor for bleeding than as an actual disease.

Patients with type 2 vWD have functional defects; thus, the vWF antigen measurement is significantly higher than the test of function. For types 2A, 2B, and 2M, vWF activity is decreased, measured as ristocetin cofactor or collagen binding activity. In type 2A vWD, the impaired function is due either to increased susceptibility to cleavage by ADAMTS13, resulting in loss of intermediate- and high-molecular weight (M.W.) multimers, or to decreased secretion of these multimers by the cell. Type 2B vWD results from gain of function mutations that result in increased spontaneous binding of vWF to platelets in circulation, with subsequent clearance of this complex by the reticuloendothelial system. The resulting vWF in the patients' plasma lacks the highest M.W. multimers, and the platelet count is usually modestly reduced. Type 2M results from a group of mutations that cause dysfunction of the molecule but do not affect multimer structure.

Type 2N vWD reflects mutations in vWF that preclude binding of FVIII. As FVIII is stabilized by binding to vWF, the FVIII in patients with type 2N vWD has a very short half-life, and the FVIII level is markedly decreased. This is sometimes termed autosomal hemophilia. Type 3 vWD, or severe vWD, describes patients with virtually no vWF antigen (usually <10%). Patients experience mucosal and joint postoperative symptoms as well as other bleeding symptoms. Some patients with type 3 vWD, particularly those with large vWF gene deletions, are at risk of developing antibodies to infused vWF.

Acquired vWD is a rare disorder, most commonly seen in patients with underlying lymphoproliferative disorders, including monoclonal gammopathies of undetermined significance (MGUS), multiple myeloma, and Waldenstrom's macroglobulinemia. It is seen most commonly in the setting of MGUS and should be suspected in patients, particularly elderly patients, with a new onset of severe mucosal bleeding symptoms.

Heyde's syndrome (aortic stenosis with gastrointestinal bleeding) is attributed to the presence of angiodysplasia of the gastrointestinal tract in patients with aortic stenosis. However, the shear stress on blood passing through the stenotic aortic valve appears to produce a change in vWF, making it susceptible to serum proteases. Consequently, large multimer forms are lost, leading to an acquired type 2 vWD, but return when the stenotic valve is replaced.

von Willebrand Disease: Treatment

The mainstay of treatment for type 1 vWD is 1-deamino-8-D-arginine vasopressin (DDAVP, or desmopressin), which results in release of vWF and FVIII from endothelial stores. DDAVP can be given intravenously or by an intranasal spray (1.5 mg/mL). The peak activity when given intravenously is approximately 30 min, while it is 2 h when given intranasally. The usual dose is 0.3 g/kg intravenously or 2 squirts (1 in each nostril) for patients >50 kg (1 squirt for those <50 kg). It is recommended that patients with vWD be tested with DDAVP to assess their response before using it.

In patients who respond well (increase in values of two- to fourfold), it can be used for procedures with minor-to-moderate risk of bleeding. Depending on the procedure, additional doses may be needed; it is usually given every 12–24 h. Less frequent dosing may result in less tachyphylaxis, which occurs when synthesis cannot compensate for the released stores. The major side effect of DDAVP is hyponatremia due to decreased free water clearance. This occurs most commonly in the very young and the very old, but fluid restriction should be advised for all patients for the 24 hours following each dose.

Some patients with types 2A and 2M vWD respond to DDAVP such that it can be used for minor procedures. For the other subtypes, for type 3 disease, and for major procedures requiring longer periods of normal hemostasis, vWF replacement can be given. Virally inactivated vWF-containing factor concentrates are thought to be safer than cryoprecipitate as the replacement product. Humate-P is the only FDA-approved product for this indication in the United States. Other concentrates have been studied in vWD, and a vWF concentrate is available in some countries in Europe.

Antifibrinolytic therapy, using either epsilon-aminocaproic acid or tranexamic acid, is an important therapy, either alone or in an adjunctive capacity, particularly for the prevention or treatment of mucosal bleeding. These agents are particularly useful in prophylaxis for dental procedures, with DDAVP for dental extractions and tonsillectomy, menorrhagia, and prostate procedures. It is contraindicated in the setting of upper urinary tract bleeding, due to the risk of ureteral obstruction.

20110822

Thrombotic Thrombocytopenic Purpura and Hemolytic Uremic Syndrome



Thrombotic thrombocytopenic microangiopathies are a group of disorders characterized by

thrombocytopenia, 
a microangiopathic hemolytic anemia evident by fragmented RBCs and 
laboratory evidence of hemolysis, and microvascular thrombosis. 

This includes thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS), as well as syndromes complicating bone marrow transplantation, certain medications and infections, pregnancy, and vasculitis. In DIC, while thrombocytopenia and microangiopathy are seen, a coagulopathy predominates, with consumption of clotting factors and fibrinogen resulting in an elevated prothrombin time (PT) and often activated partial thromboplastin time (aPTT). The PT and aPTT are characteristically normal in TTP or HUS.




Thrombotic Thrombocytopenic Purpura


TTP and HUS were previously considered overlap syndromes. However, in the past few years the pathophysiology of inherited and idiopathic TTP has become better understood and clearly differs from HUS. TTP was first described in 1924 by Eli Moschcowitz and characterized by a pentad of findings that include microangiopathic hemolytic anemia, thrombocytopenia, renal failure, neurologic findings, and fever. The full-blown syndrome is less commonly seen now, probably due to earlier diagnosis. The introduction of treatment with plasma exchange markedly improved the prognosis in patients, with a decrease in mortality from 85–100% to 10–30%.

The pathogenesis of inherited (Upshaw-Schulman syndrome) and idiopathic TTP is related to a deficiency of, or antibodies to, a metalloprotease that cleaves vWF and ADAMTS13, respectively.

vWF is normally secreted as ultra-large multimers, which are then cleaved by ADAMTS13. The persistence of ultra-large vWF molecules are thought to contribute to pathogenic platelet adhesion and aggregation . This defect alone, however, is not sufficient to result in TTP as individuals with a congenital absence of ADAMTS13 develop TTP only episodically. Additional provocative factors have not been defined. The level of ADAMTS13 activity, as well as antibodies, can now be detected by laboratory assays. However, assays with sufficient sensitivity and specificity to direct clinical management have yet to be defined.

Figure



Pathogenesis of thrombotic thrombocytopenic purpura (TTP).

 Normally the ultra-high molecular-weight multimers of von Willebrand factor (vWF) produced by the endothelial cells are processed into smaller multimers by a plasma metalloproteinase called ADAMTS13. In TTP the activity of the protease is inhibited, and the ultra-high molecular-weight multimers of vWF initiate platelet aggregation and thrombosis.

Idiopathic TTP appears to be more common in women than in men. No geographic or racial distribution has been defined. TTP is more common in patients with HIV infection and in pregnant women.

 Medication-related TTP may be secondary to antibody formation (ticlopidine and possibly clopidogrel) or direct endothelial toxicity (cyclosporine, mitomycin C, tacrolimus, quinine), although this is not always so clear, and fear of withholding treatment, as well as lack of other treatment alternatives, results in broad application of plasma exchange. However, withdrawal, or reduction in dose, of endothelial toxic agents may decrease the microangiopathy.

Thrombotic Thrombocytopenic Purpura: Treatment

TTP is a devastating disease if not diagnosed and treated promptly. In patients presenting with new thrombocytopenia, with or without evidence of renal insufficiency and other elements of classic TTP, laboratory data should be obtained to rule out DIC and to evaluate for evidence of microangiopathic hemolytic anemia.

 Findings to support the TTP diagnosis include an
increased lactate dehydrogenase
 indirect bilirubin,
 decreased haptoglobin, 
increased reticulocyte count
negative direct antiglobulin test.

The peripheral smear should be examined for evidence of schistocytes (Fig. 109-1D). Polychromasia is usually also present due to the increased number of young red blood cells, and nucleated RBCs are often present, which is thought to be due to infarction in the microcirculatory system of the bone marrow.


Plasma exchange remains the mainstay of treatment of ITP. ADAMTS13 antibody–mediated TTP (idiopathic TTP) appears to respond best to plasma exchange. Plasma exchange is continued until the platelet count is normal and signs of hemolysis are resolved for at least 2 days. While never evaluated in clinical trial, the use of glucocorticoids seems a reasonable approach, but they should only be used as an adjunct to plasma exchange. Additionally, other immunomodulatory therapies have been reported to be successful in refractory or relapsing TTP, including rituximab, vincristine, cyclophosphamide, and splenectomy. The role of rituximab in the treatment of this disorder needs to be defined. A significant relapse rate is noted: 25–45% within 30 days of initial "remission" and 12–40% with late relapses. Relapses may be more frequent in patients with severe ADAMTS13 deficiency at presentation.

Hemolytic Uremic Syndrome


HUS is a syndrome characterized by acute renal failure, microangiopathic hemolytic anemia, and thrombocytopenia. It is seen predominantly in children and in most cases is preceded by an episode of diarrhea, often hemorrhagic in nature. Escherichia coli O157:H7 is the most frequent, although not only, etiologic serotype. HUS not associated with diarrhea (termed D-HUS) is more heterogeneous in presentation and course. Some children who develop D-HUS have been found to have mutations in genes encoding Factor H, a soluble complement regulator, and membrane cofactor protein that is mainly expressed in the kidney.

Hemolytic Uremic Syndrome: Treatment


Treatment of HUS is primarily supportive. In D+HUS, many (~40%) children require at least some period of support with dialysis; however, the overall mortality is <5%. In D–HUS the mortality is higher, approximately 26%. Plasma infusion or plasma exchange has not been shown to alter the overall course. ADAMTS13 levels are generally reported to be normal in HUS, although occasionally they have been reported to be decreased. As ADAMTS13 assays improve, they may help in defining a subset that better fits a TTP diagnosis and may respond to plasma exchange.

Immune Thrombocytopenic Purpura (ITP)


Immune thrombocytopenic purpura (ITP; also termed idiopathic thrombocytopenic purpura) is an acquired disorder leading to immune-mediated destruction of platelets and possibly inhibition of platelet release from the megakaryocyte. In children it is usually an acute disease, most commonly following an infection, and with a self-limited course. In adults it usually runs a more chronic course.

The exact nature of the immune dysfunction is generally not known. ITP is termed secondary if it is associated with an underlying disorder; autoimmune disorders, particularly systemic lupus erythematosis (SLE), and infections, such as HIV and hepatitis C, are common causes. The association of ITP with Helicobacter pylori infection is unclear.

ITP is characterized by mucocutaneous bleeding and a low, often very low, platelet count, with otherwise normal peripheral blood cells and smear. Patients usually present either with ecchymoses and petechiae, or with thrombocytopenia incidentally found on a routine CBC. Mucocutaneous bleeding, such as oral mucosa, gastrointestinal, or heavy menstrual bleeding, may be present. Rarely, life-threatening bleeding, including in the central nervous system, can occur. Wet purpura (blood blisters in the mouth) and retinal hemorrhages may herald life-threatening bleeding.

Laboratory Testing in ITP


Laboratory testing for antibodies (serologic testing) is usually not helpful due to the low sensitivity and specificity of the tests. Bone marrow examination can be reserved for older adults (usually >60 years) or those who have other signs or laboratory abnormalities not explained by ITP, or in patients who do not respond to initial therapy. The peripheral blood smear may show large platelets, with otherwise normal morphology. Depending on the bleeding history, iron deficiency anemia may be present.

Laboratory testing is performed to evaluate for secondary causes of ITP and should include testing for HIV infection and hepatitis C (and other infections if indicated); serologic testing for SLE; serum protein electrophoresis and immunoglobulin levels to potentially detect hypogammaglobulinemia, IgA deficiency, or monoclonal gammopathies; and, if anemia is present, direct antiglobulin testing (Coombs test) to rule out combined autoimmune hemolytic anemia with ITP (Evans's syndrome).


Immune Thrombocytopenic Purpura: Treatment

The treatment of ITP utilizes drugs that decrease reticuloendothelial uptake of the antibody-bound platelet and/or decrease antibody production. However, the diagnosis of ITP does not necessarily mean that treatment must be instituted. Patients with platelet counts >30,000/L appear not to have increased mortality related to the thrombocytopenia.

Initial treatment in patients without significant bleeding symptoms, severe thrombocytopenia (<5000/L), or signs of impending bleeding (such as retinal hemorrhage or large oral mucosal hemorrhages) can be instituted as an outpatient using single agents. Traditionally this has been prednisone at 1 mg/kg, although Rh0(D) immune globulin therapy (WinRho SDF) at 50–75 g/kg is also being used in this setting. Rh0(D) immune globulin must be used only in Rh+ patients as the mechanism of action is production of limited hemolysis, with antibody-coated cells "saturating" the Fc receptors, inhibiting Fc receptor function. Hemoglobin levels usually decrease (mean 1.7 g/dL), although severe intravascular hemolysis is a rare complication. Doses are reduced if given to anemic patients. Intravenous gamma globulin (IVIgG), which is pooled, primarily IgG antibodies, also blocks the Fc receptor system, but appears to work primarily through different mechanism(s). IVIgG has more efficacy than anti-Rh0(D) in post-splenectomized patients. IVIgG is dosed at 2 g/kg total, given in divided doses over 2–5 days. Side effects are usually related to the volume of infusion and infrequently include aseptic meningitis and renal failure. All immunoglobulin preparations are derived from human plasma and undergo treatment for viral inactivation.

For patients with severe ITP and/or symptoms of bleeding, hospital admission and combined modality therapy are given using high-dose glucocorticoids with IVIgG or anti-Rh0D therapy, and, as needed, additional immunosuppressive agents. Rituximab, an anti-CD20 (B cell) antibody, has shown efficacy in the treatment of refractory ITP.


Splenectomy has been used for treatment of patients who relapse after glucocorticoids are tapered. Splenectomy remains an important treatment option; however, more patients than previously thought will go into a remission over time. Observation, if the platelet count is high enough, or intermittent treatment with anti-Rh0(D) or IVIgG may be a reasonable approach to see if the ITP will resolve.


Vaccination against encapsulated organisms (especially pneumococcus, but also menningococcus and Haemophilus influenzae, depending on patient age and potential exposure) is recommended before splenectomy. Accessory spleen(s) are a very rare cause of relapse.

New drugs for ITP include TPO receptor agonists. This approach to treatment of ITP stems from the finding that many patients with ITP do not have increased TPO levels, as was previously hypothesized, nor do they all have increased platelet destruction. Two agents, one administered subcutaneously and another orally, have shown response in many patients with refractory ITP. Roles for these agents in ITP treatment are not fully defined.

Heparin-Induced Thrombocytopenia


Drug-induced thrombocytopenia due to heparin differs from that seen with other drugs in two major ways.

(1) The thrombocytopenia is not usually severe, with nadir counts rarely <20,000/L.

(2) Heparin-induced thrombocytopenia (HIT) is not associated with bleeding and, in fact, markedly increases the risk of thrombosis.

HIT results from antibody formation to a complex of the platelet-specific protein platelet factor 4 (PF4) and heparin. The antiheparin/PF4 antibody can activate platelets through the FcRIIa receptor and also likely activates endothelial cells. Many patients exposed to heparin develop antibodies to heparin/PF4, but do not appear to have adverse consequences. A fraction of those who develop antibodies will develop thrombocytopenia, and a portion of those (up to 50%) will develop HIT and thrombosis (HITT).

HIT can occur after exposure to low-molecular-weight heparin (LMWH), as well as unfractionated heparin (UFH), although it is about 10 times more common with the latter. Most patients develop HIT after exposure to heparin for 5–10 days (Fig. 109-3). It occurs before 5 days only in those who were exposed to heparin in the prior few weeks or months (< ~100 days) and have circulating antiheparin/PF4 antibodies. Rarely, thrombocytopenia and thrombosis begin several days after all heparin has been stopped (termed delayed onset HIT). The 4 "T"s have been recommended to be used in a diagnostic algorithm for HIT: thrombocytopenia, timing of platelet count drop, thrombosis and other sequelae such as localized skin reactions, and other cause of thrombocytopenia not evident.


Time course of heparin-induced thrombocytopenia (HIT) development after heparin exposure. The timing of development after heparin exposure is a critical factor in determining the likelihood of HIT in a patient. HIT occurs early in heparin exposure only in the presence of preexisting heparin/platelet factor 4 (PF4) antibodies, which disappear from circulation by ~100 days following a prior exposure. Rarely, HIT may occur later after heparin exposure (termed delayed-onset HIT). In this setting, heparin/PF4 antibody testing is markedly positive. HIT can occur after exposure to either unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH).

Laboratory Testing for HIT


HIT (antiheparin/PF4) antibodies can be detected using two types of assays. The most widely available is an enzyme-linked immunoassay (ELISA) with PF4/polyanion complex as the antigen. Since many patients develop antibodies but do not develop clinical HIT, the test has a low specificity for the diagnosis of HIT. This is especially true in patients who have undergone cardiopulmonary bypass surgery, where approximately 50% of patients develop these antibodies postoperatively. The other assay is a platelet activation assay that measures the ability of the patients' serum to activate platelets in the presence of heparin in a concentration-dependent manner. This test has lower sensitivity but higher specificity than the ELISA. However, HIT remains a clinical diagnosis. The main value in testing is in excluding the diagnosis with negative tests, particularly ELISA.


Heparin-Induced Thrombocytopenia: Treatment


Early recognition is key in treatment of HIT, with prompt discontinuation of heparin and use of alternative anticoagulants. Thrombosis is a common complication of HIT, even after heparin discontinuation, and can occur in both the venous and arterial systems. In patients diagnosed with HIT, imaging studies to evaluate the presence of thrombosis (at least lower-extremity duplex dopplers) are recommended.

Patients requiring anticoagulation should be switched from heparin to an alternative anticoagulant. The direct thrombin inhibitors (DTIs) argatroban and lepirudin are effective in HITT. The DTI bivalirudin and the antithrombin-binding pentasaccharide fondaparinux appear to be effective but are not yet approved by the U.S. Food and Drug Administration (FDA) for this indication. Danaparoid, a mixture of glycosoaminoglycans with anti-Xa activity, has been used extensively for the treatment of HITT; it is no longer available in the United States but is in other countries. HIT antibodies cross-react with LMWH, and these preparations should not be used in the treatment of HIT.

Because of the high rate of thrombosis in patients with HIT, anticoagulation should be strongly considered, even in the absence of thrombosis. In patients with thrombosis, patients can be transitioned to warfarin, with treatment usually for 3–6 months. In patients without thrombosis, the duration of anticoagulation needed is undefined. An increased risk of thrombosis is present for at least 1 month after diagnosis; however, most thromboses occur early, and whether thrombosis occurs later if the patient is initially anticoagulated is unknown. Options include continuing anticoagulation until a few days after platelet recovery or for one month. Introduction of warfarin alone in the setting of HIT or HITT may precipitate thrombosis, particularly venous gangrene, presumably due to clotting activation and severely reduced levels of proteins C and S. Warfarin should only be started after alternative anticoagulation has been given for several days and the prothrombotic state has lessened.

Drugs Definitively Reported to Cause Isolated Thrombocytopenia


Isolated Thrombocytopenia:   Drugs that preceded thrombocytopenia and full recovery occurred after drug discontinuation, but recurred with re-introduction of the drug, and other causes, including other drugs were excluded.

Abciximab
Digoxin
Acetaminophen
Eptifibatide
Acyclovir
Hydrochlorothiazide
Aminosalicylic acid
Ibuprofen
Amiodarone
Levamisole
Amphotericin B
Octreotide
Ampillicin
Phenytoin
Carbamazepine
Quinine
Chlorpropamide
Rifampin
Danazol
Tamoxifen
Diatrizoate meglumine (Hypaque Meglumine)
Tirofiban
Trimethoprim/sulfamethoxazole
Diclofenac
Vancomycin

Thrombocytopenia-Evaluation


Human Immunodeficiency Virus


HIV-associated nephropathy is seen after an interval of approximately 2.5 years from discovery of HIV, and many patients have low CD4 counts. Most lesions on renal biopsy show FSGS followed by MPGN. Other less common renal lesions include DPGN, IgA nephropathy, MCD, and membranous or mesangioproliferative glomerulonephritis.

 The disease affects up to 10% of HIV-infected patients and is more commonly seen in African-American men than in Caucasians, and in intravenous drug users or homosexuals. The FSGS characteristically reveals collapse of the glomerular capillary tuft called collapsing glomerulopathy, visceral epithelial cell swelling, microcystic dilatation of renal tubules, and tubuloreticular inclusions. Renal epithelial cells express replicating HIV virus, but host immune responses also play a role in the pathogenesis. MPGN and DPGN have been reported more commonly in HIV-infected Caucasians and in patients co-infected with hepatitis B or C. HIV-associated TTP has also been reported.
HIV patients with FSGS typically present with nephrotic-range proteinuria and hypoalbuminemia, but unlike patients with other etiologies for nephrotic syndrome, they do not commonly have hypertension, edema, or hyperlipidemia. Renal ultrasound also reveals large, echogenic kidneys, and renal function in some patients declines rapidly.

 Treatment with inhibitors of the renin-angiotensin system decreases the proteinuria. Although evidence from large well-designed clinical trials is lacking, many feel that effective antiretroviral therapy benefits both the patient and the kidney. Dismal survival once renal failure is reached has improved, and many centers now offer renal allografts to select HIV patients.

Thrombotic Microangiopathies


Thrombotic thrombocytopenic purpura (TTP) and hemolytic-uremic syndrome (HUS) represent a spectrum of thrombotic microangiopathies.

TTP and HUS share the general features of idiopathic thrombocytopenic purpura, hemolytic anemia, fever, renal failure, and neurologic disturbances. When patients have more evidence of renal injury, their condition tends to be called HUS, and when there is more neurologic disease, it is considered to be TTP. In adults there is often a mixture of both, which is why they are often called TTP/HUS.

On examination of kidney tissue there is evidence of glomerular capillary endotheliosis associated with platelet thrombi, damage to the capillary wall, and formation of fibrin material in and around glomeruli . These tissue findings are similar to what is seen in preeclampsia/HELLP (hemolysis, elevated liver enzymes, and low platelet count syndrome), malignant hypertension, and the antiphospholipid syndrome. TTP/HUS is also seen in pregnancy; with the use of oral contraceptives or quinine; in renal transplant patients given OKT3 for rejection; in patients taking the calcineurin inhibitors cyclosporine and tacrolimus or in patients taking the antiplatelet agents ticlopidine and clopidogrel; or following HIV infection.

Although there is no agreement on how much they share a final common pathophysiology, two general groups of patients are recognized:
a) childhood HUS associated with enterohemorrhagic diarrhea and
b) TTP-HUS in adults.

Childhood HUS is caused by a toxin released by Escherichia coli O157:H7 and occasionally by Shigella dysenteriae. This shiga toxin (veratoxin) directly injures endothelia, enterocytes, and renal cells, causing apoptosis, platelet clumping, and intravascular hemolysis by binding to the glycolipid receptors (Gb3). These receptors are more abundant along endothelia in children compared to adults.

In familial cases of adult TTP/HUS, there is a genetic deficiency of the ADAMTS13 metalloprotease that cleaves large multimers of von Willebrand's factor. Absent ADAMTS13, these large multimers cause platelet clumping and intravascular hemolysis. An antibody to ADAMTS13 is found in many sporadic cases of adult TTP/HUS, but not all; many patients also have antibodies to the thrombospondin receptor on selected endothelial cells in small vessels or increased levels of plasminogen-activator inhibitor 1 (PAI-1).

The treatment of childhood HUS or adult TTP/HUS is daily plasmapheresis, which can be lifesaving. Plasmapheresis is given until the platelet count rises, but in relapsing patients it may need to be continued well after the platelet count improves, and in resistant patients twice-daily exchange may be helpful. Most patients respond within 2 weeks of daily plasmapheresis. Since TTP/HUS often has an autoimmune basis, there is an anecdotal role in relapsing patients for using splenectomy, steroids, immunosuppressive drugs, or anti-CD20 antibody. Patients with childhood HUS from infectious diarrhea are not given antibiotics, as antibiotics are thought to accelerate the release of the toxin and the diarrhea is usually self-limited.

Alport's Syndrome


Classically, patients with Alport's syndrome develop hematuria, thinning and splitting of the GBMs, mild proteinuria (<1–2 g/24 h), and chronic glomerulosclerosis, leading to renal failure in association with sensorineural deafness. Some patients develop lenticonus of the anterior lens capsule and, rarely, mental retardation or leiomyomatosis.

 Approximately 85% of patients with Alport's syndrome have an X-linked inheritance of mutations in the alpha 5(IV) collagen chain on chromosome Xq22–24. Female carriers have variable penetrance depending on the type of mutation or the degree of mosaicism created by X inactivation. Fifteen percent of patients have autosomal recessive disease of the 3(IV) or 4(IV) chains on chromosome 2q35–37. Rarely, some kindred have an autosomal dominant inheritance of dominant-negative mutations in 3(IV) or 4(IV) chains.
Pedigrees with this syndrome are quite variable in their rate and frequency of tissue damage leading to organ failure. Patients with nonsense or missense mutations, reading frame shifts, or large deletions generally develop renal failure and sensorineural deafness by age 30 (juvenile form), while patients with splice variants, exon skipping, or missense mutations of -helical glycines generally deteriorate after the age of 30 (adult form) with mild or late deafness. Early severe deafness or lenticonus suggest a poorer prognosis. 
Alport's patients early in their disease typically have thin basement membranes on renal biopsy , which thicken over time into multilamellations surrounding lucent areas that often contain granules of varying density—the so-called split basement membrane. In any Alport kidney there are areas of thinning mixed with splitting of the GBM. Tubules drop out, glomeruli scar, and the kidney eventually succumbs to interstitial fibrosis.

Primary treatment is control of systemic hypertension and use of ACE inhibitors to slow renal progression. Although patients who receive renal allografts usually develop anti-GBM antibodies directed toward the collagen epitopes absent in their native kidney, overt Goodpasture's syndrome is uncommon and graft survival is good.

Thin Basement Membrane Disease


Some variants of Alport's syndrome are now recognized as a subpopulation of patients with thin basement membrane disease. Thin basement membranes are found in 5–10% of the so-called normal population. These subclinical patients have normal blood pressure and little proteinuria, and they rarely progress to renal failure. If they present with hematuria, they are often given the diagnosis of benign familial hematuria. Many of these patients have mutations in the same 3(IV) or 4(IV) collagen genes associated with autosomal recessive or dominant Alport's syndrome. Clearly, the boundary between nonprogressive Alport's syndrome and benign familial hematuria is quite variable, as there is a spectrum of clinical penetrance.

Collagen IV

 The extended family of collagen IV contains six chains, which are expressed in different tissues at different stages of embryonic development.

All epithelial basement membranes early in human development are composed of interconnected triple-helical protomers rich in alpha-1.alpha-1.alpha-2(IV) collagen.

Some specialized tissues undergo a developmental switch replacing a1.a1.a2(IV) protomers with an a3.a4.a5(IV) collagen network; this switch occurs in the kidney (glomerular and tubular basement membrane), lung, testis, cochlea, and eye, while an
a5.a5.a6(IV) network appears in skin, smooth muscle, and esophagus and along Bowman's capsule in the kidney.

This switch probably occurs because the a3.a4.a5(IV) network is more resistant to proteases and ensures the structural longevity of critical tissues.

Fabry's Disease


Fabry's disease is an X-linked inborn error of globotriaosylceramide metabolism secondary to deficient lysosomal -galactosidase A activity, resulting in excessive intracellular storage of globotriaosylceramide.

Affected organs include the vascular endothelium, heart, brain, and kidneys. Classically, Fabry's disease presents in childhood in males with multi-organ involvement. Hemizygotes with hypomorphic mutations sometimes present in the fourth to sixth decade with single organ involvement. Rarely, dominant-negative -galactosidase A mutations or female heterozygotes with unfavorable X inactivation present with mild single-organ involvement.

 Renal biopsy reveals enlarged glomerular visceral epithelial cells packed with small clear vacuoles containing globotriaosylceramide; vacuoles may also be found in parietal and tubular epithelia . These vacuoles of electron-dense materials in parallel arrays (zebra bodies) are easily seen on electron microscopy. Ultimately, glomeruli develop FSGS. The nephropathy of Fabry's disease typically presents in the third decade as mild to moderate proteinuria, sometimes with microscopic hematuria or nephrotic syndrome. Urinalysis may reveal oval fat bodies and birefringent glycolipid globules under polarized light (Maltese cross). Renal biopsy is necessary for definitive diagnosis. Progression to renal failure occurs by the fourth or fifth decade.

 Treatment with recombinant -galactosidase A has been demonstrated to clear microvascular endothelial deposits of globotriaosylceramide from the kidneys, heart, and skin.

Mne: Lyso (young boy) is riding to the gal-a on a zebra wearing a fabric printed with focal segments of three bowls of ceramic around a maltese cross.

Renal Amyloidosis


Most renal amyloidosis is either the result of

primary fibrillar deposits of immunoglobulin light chains [amyloid L (AL)],
or
secondary to fibrillar deposits of serum amyloid A (AA) protein fragments .

Even though both occur for different reasons, their clinicopathophysiology is quite similar and will be discussed together. Amyloid infiltrates the liver, heart, peripheral nerves, carpal tunnel, upper pharynx, and kidney, producing restrictive cardiomyopathy, hepatomegaly, macroglossia, and heavy proteinuria sometimes associated with renal vein thrombosis.

In systemic AL amyloidosis, also called primary amyloidosis, light chains produced in excess by clonal plasma cell dyscrasias are made into fragments by macrophages so they can self-aggregate at acid pH. A disproportionate number of these light chains (75%) are of the lambda class. About 10% of these patients have overt myeloma with lytic bone lesions and infiltration of the bone marrow with >30% plasma cells; nephrotic syndrome is common, and about 20% of patients progress to dialysis.

 AA amyloidosis is sometimes called secondary amyloidosis and also affects the kidney with nephrotic syndrome. It is due to deposition of beta-pleated sheets of serum amyloid A protein, an acute phase reactant whose physiologic function is unknown. Forty percent of patients with AA amyloid have rheumatoid arthritis, and another 10% have ankylosing spondylitis or psoriatic arthritis; the rest derive from other lesser causes. Less common in Western countries but more common in Mediterranean regions, particularly in Sephardic and Iraqi Jews, is familial Mediterranean fever (FMF). FMF is caused by a mutation in the gene encoding pyrin, while Muckle-Wells syndrome, a related disorder, results from a mutation in cryropyrin; both proteins are important in the apoptosis of leukocytes early in inflammation. Receptor mutations in TNFR1–associated periodic syndrome also produce chronic inflammation and secondary amyloidosis. Fragments of serum amyloid A protein increase and self-aggregate by attaching to receptors for advanced glycation end products in the extracellular environment; nephrotic syndrome is common, and about 40–60% of patients progress to dialysis.

 AA and AL amyloid fibrils are detectable with Congo red or in more detail with electron microscopy . Biopsy of involved liver or kidney is diagnostic 90% of the time when the pretest probability is high; abdominal fat pad aspirates are positive about 70% of the time, but apparently less so when looking for AA amyloid. Amyloid deposits are distributed along blood vessels and in the mesangial regions of the kidney.

The treatment for primary amyloidosis is not particularly effective; melphalan and autologous hematopoietic stem cell transplantation can delay the course of disease in about 30% of patients. Secondary amyloidosis is also relentless unless the primary disease can be controlled. Some new drugs in development that disrupt the formation of fibrils may be available in the future.

Diabetic Nephropathy


Diabetic nephropathy is the single most common cause of chronic renal failure in the United States, accounting for 45% of patients receiving renal replacement therapy, and is a rapidly growing problem worldwide. The dramatic increase in the number of patients with diabetic nephropathy reflects the epidemic increase in obesity, metabolic syndrome, and Type 2 diabetes mellitus.

Approximately 40% of patients with Types 1 or 2 diabetes develop nephropathy, but due to the higher prevalence of Type 2 diabetes (90%) compared to Type 1 (10%), the majority of patients with diabetic nephropathy have Type 2 disease. Renal lesions are more common in African-American, Native American, Polynesian, and Maori populations.

Risk factors for the development of diabetic nephropathy :include hyperglycemia, hypertension, dyslipidemia, smoking, a family history of diabetic nephropathy, and gene polymorphisms affecting the activity of the renin-angiotensin-aldosterone axis.

Within 1–2 years after the onset of clinical diabetes, morphologic changes appear in the kidney. Thickening of the GBM is a sensitive indicator for the presence of diabetes but correlates poorly with the presence or absence of clinically significant nephropathy. The composition of the GBM is altered notably with a loss of heparan sulfate moieties that form the negatively charged filtration barrier. This change results in increased filtration of serum proteins into the urine, predominately negatively charged albumin. The expansion of the mesangium due to the accumulation of extracellular matrix correlates with the clinical manifestations of diabetic nephropathy. This expansion in mesangial matrix can be associated with the development of mesangial sclerosis. Some patients also develop eosinophilic, PAS+ nodules called nodular glomerulosclerosis or Kimmelstiel-Wilson nodules.

 Immunofluorescence microscopy often reveals the nonspecific deposition of IgG (at times in a linear pattern) or complement staining without immune deposits on electron microscopy. Prominent vascular changes are frequently seen with hyaline and hypertensive arteriosclerosis. This is associated with varying degrees of chronic glomerulosclerosis and tubulointerstitial changes. Renal biopsies from patients with Types 1 and 2 diabetes are largely indistinguishable.
These pathologic changes are the result of a number of postulated factors. Multiple lines of evidence support an important role for increases in glomerular capillary pressure (intraglomerular hypertension) in alterations in renal structure and function. Direct effects of hyperglycemia on the actin cytoskeleton of renal mesangial and vascular smooth-muscle cells as well as diabetes-associated changes in circulating factors such as atrial naturetic factor, angiotensin II, and insulin-like growth factor (IGF) may account for this. Sustained glomerular hypertension increases matrix production, alterations in the GBM with disruption in the filtration barrier (and hence proteinuria) and glomerulosclerosis. A number of factors have also been identified which alter matrix production, including the accumulation of advanced glycosylation end products, circulating factors including growth hormone, IGF-I, angiotensin II, connective tissues growth factor, TGF-, and dyslipidemia.

The natural history of diabetic nephropathy in patients with Types 1 and 2 diabetes is similar. However, since the onset of Type 1 diabetes is readily identifiable and the onset of Type 2 diabetes is not, a patient newly diagnosed with Type 2 diabetes may have renal disease for many years before nephropathy is discovered and presents as advanced diabetic nephropathy. At the onset of diabetes, renal hypertrophy and glomerular hyperfiltration are present. The degree of glomerular hyperfiltration correlates with the subsequent risk of clinically significant nephropathy. In the approximately 40% of patients with diabetes who develop diabetic nephropathy, the earliest manifestation is an increase in albuminuria detected by sensitive radioimmunoassay. Albuminuria in the range of 30–300 mg/24 h is called microalbuminuria.

In patients with Types 1 or 2 diabetes, microalbuminuria appears 5–10 years after the onset of diabetes. It is currently recommended to test patients with Type 1 disease for microalbuminuria 5 years after diagnosis of diabetes and yearly thereafter, and, because the time of onset of Type 2 diabetes is often unknown, to test Type 2 patients at the time of diagnosis of diabetes and yearly thereafter.
Patients with small rises in albuminuria increase their levels of urinary albumin excretion, typically reaching dipstick positive levels of proteinuria (>300 mg albuminuria) 5–10 years after the onset of early albuminuria.

 Microalbuminuria is a potent risk factor for cardiovascular events and death in patients with Type 2 diabetes. Many patients with Type 2 diabetes and microalbuminuria succumb to cardiovascular events before they progress to proteinuria or renal failure. Proteinuria in frank diabetic nephropathy can be variable, ranging from 500 mg to 25 g/24 h, and is often associated with nephrotic syndrome. More than 90% of patients with Type 1 diabetes and nephropathy have diabetic retinopathy, so the absence of retinopathy in Type 1 patients with proteinuria should prompt consideration of a diagnosis other than diabetic nephropathy; only 60% of patients with Type 2 diabetes with nephropathy have diabetic retinopathy. There is a highly significant correlation between the presence of retinopathy and the presence of Kimmelstiel-Wilson nodules . Also, characteristically, patients with advanced diabetic nephropathy have normal to enlarged kidneys, in contrast to other glomerular diseases where kidney size is usually decreased. Using the above epidemiologic and clinical data, and in the absence of other clinical or serologic data suggesting another disease, diabetic nephropathy is usually diagnosed without a renal biopsy.

After the onset of proteinuria >500 mg/24 h, renal function inexorably declines, with 50% of patients reaching renal failure in 5–10 years; thus, from the earliest stages of microalbuminuria, it usually takes 10–20 years to reach end-stage renal disease. Hypertension may predict which patients develop diabetic nephropathy, as the presence of hypertension accelerates the rate of decline in renal function. Once renal failure appears, however, survival on dialysis is far shorter for patients with diabetes compared to other dialysis patients; some diabetics do better clinically if they are started on dialysis before they reach advanced renal failure. Survival is best for patients with Type 1 diabetes who receive a transplant from a living related donor. 
Good evidence supports the benefits of blood sugar and blood pressure control as well as inhibition of the renin-angiotensin system in retarding the progression of diabetic nephropathy. In patients with Type 1 diabetes, intensive control of blood sugar clearly prevents the development or progression of diabetic nephropathy. The evidence in patients with Type 2 disease, although less compelling, also supports intensive control of blood sugar. Controlling systemic blood pressure to levels of 130/80 mmHg or less decreases renal and cardiovascular adverse events in this high-risk population. The vast majority of patients with diabetic nephropathy require three or more antihypertensive drugs to achieve this goal. Drugs that inhibit the renin-angiotensin system, independent of their effects on systemic blood pressure, have been repeatedly shown to slow the progression of diabetic nephropathy at early (microalbuminuria) and late (proteinuria with reduced glomerular filtration) stages, independent of any effect they may have on systemic blood pressure.

Since angiotensin II increases efferent arteriolar resistance and, hence, glomerular capillary pressure, one key mechanism for the efficacy of ACE inhibitors or angiotensin receptor blockers (ARBs) is reducing glomerular hypertension. Patients with Type 1 diabetes for 5 years who develop albuminuria or declining renal function should be treated with ACE inhibitors. Patients with Type 2 diabetes and microalbuminuria or proteinuria may be treated with ACE inhibitors or ARBs.

20110821

Sample qn 5-20

Question :

5.The intrinsic enzyme activity associated with the alpha subunit of regulatory G-protein is a:
 
Options:
 
Kinase that transfers the gamma-phosphate of GTP to serine residues of proteins.
GTPase that hydrolyzes GTP to GDP.
Guanylate cyclase that converts GTP to cGMP.
cGMP dependent kinase


6.Vitamin K is required to carboxylate the following amino acid residue of clotting factors:
 
Options:
 
Glutamate.
Aspartate.
Histamine.
Kistamine.


7. Which of the following is not associated with carbohydrate antigen?
 
Options:
 
 Polyclonal B cell stimulation.
Memory response.
T-independent immune response.
Poor immunogenecity.
 
8. Cellular energy generation is severely compromised in thiamine deficiency because thiamine pyrophosphate (TPP) is:
 
Options:
 
A major co-factor for oxidation-reduction reactions.
 An essential co-factor for pyruvate and alphaketoglutarate dehydrogenases.
Co-factor for transketolase
Necessary for utilizing amino acid for energy via transamination.


9.The mechanism that permits immunoglobulins to be synthesized in either a membrane bound or secreted form is:
 
Options:
 
Allelic exclusion.
Class-switching.
Differential RNA processing.
The one turn/two turn joining rule.


10.Folding of newly synthesized proteins is accelerated by all except:
 
Options:
 
Protein disulphide isomerase.
Zinc finger motifs
Prolyl cis-trans isomerase.
Chaperons.



11. In the Lac Operon, CAP (catabolite gene activation protein) is responsible for its:
 
Options:
 
Positive regulation.
Negative regulation.
Constitutive expression.
Attenuation.


12. Glutathione does all the functions except:
 
Options:
 
Convert hemoglobin to methemoglobin.
Scavenge peroxides and free radicals.
Form sulphur conjugates for detoxication of compounds.
Act as a cofactor for some enzymes.



13.Isotypic determinants are:
 
Options:
 
Subtle amino acid differences encoded by different alleles of isotype genes.
Constant region determinants distinguishing each Ig class and subclass.
Generated by conformation of amino acid sequences of the heavy and light chain variable regions.
Regions present on antigens and specifically bind to antibody



14. One of the following is not a second messenger:
 
Options:
 
Cyclic AMP.
Guanylyl cyclase.
Diacylglycerol.
Inositol triphosphate
 


15. Pertussin Toxin does not lead to:
 
Options:
 
ADP -ribosylation of G alpha-one protein.
Inhibition of adenylyl cyclase.
 Opening of Ca channels.
Decreased affinity of G protein for GTP.



16. The mechanism that permits immunoglobulins to be synthesized in either a membrane bound or secreted form is:
 
Options:
 
Co-dominant expression.
Class switching.
Allelic - exclusion.
Differential RNA processing.



17.Ribosomes have which of the following enzymatic activity:
 
Options:
 
GTPase
tRNA Aminoacyl synthetase
Peptidyl Transferase.
Peptidase


Question :
18.Actin, heat shock protein 70 and hexokinase are homologous because they:
 
Options:
 
Belong to the same fold family but have different functions
Do not belong to the same superfamily.
Evolved from a common gene.
Have similar functions but derived from different ancestral genes.



19.Mineralocorticoid receptors are present in all except
 
Options:
 
Colon
Distal nephron.
Hippocampus
Liver



20.Prions are infectious proteins that:
 
Options:
 
Are virus-coded.
Cleave proteins.
Catalyze differently folded state of a protein.
Protect disulfide bonds from being oxidized.

Sample qn 4

Question :

4. The inhibitor which inhibits protein synthesis both in eukaryotes and prokaryotes is :
 
Options:
 
Diphtheria toxin.
Puromycin.
Fusidic acid.
Chloramphenicol.