Hereditary nephritis, deafness and abnormal thrombopoiesis. Study of a new kindred

Proplatelet formation deficit and megakaryocyte death contribute to thrombocytopenia in Myh9 knockout mice

BACKGROUND

 Inactivation of the mouse Myh9 gene (Myh9Δ) or its mutation in MYH9-related diseases leads to macrothrombocytopenia. Paradoxically, previous studies using in vitro differentiated megakaryocytes showed an increased capacity for proplatelet formation when myosin was absent or inhibited.

METHODS

 To explore the origin of the thrombocytopenia induced by myosin deficiency, we studied proplatelet formation using bone marrow explants of wild-type (WT) and Myh9Δ mouse where megakaryocytes have matured in their native environment.

RESULTS AND DISCUSSION

 A dramatic decrease in the number and complexity of proplatelets was observed in megakaryocytes from Myh9Δ mice, while inhibition of myosin activity by blebbistatin increased proplatelet formation from WT mature megakaryocytes. Moreover, Myh9Δ megakaryocytes had a smaller size than the WT cells. These data indicate that myosin deficiency acts negatively on proplatelet formation, probably by impairing in situ megakaryocyte maturation, while myosin activity is dispensable at the latest stage of proplatelet formation. In addition, ultrastructural examination of Myh9Δ bone marrow revealed an increased proportion of megakaryocytes exhibiting signs of non-apoptotic cell death as compared with the WT mice.

CONCLUSION

 These data indicate that thrombocytopenia in Myh9Δ mice results from defective development of megakaryocyte size, impaired proplatelet formation and increased cell death.

Abnormal megakaryocyte morphology and proplatelet formation in mice with megakaryocyte-restricted MYH9 inactivation

Mutations in the MYH9 gene encoding nonmuscle myosin IIA lead to macrothrombocytopenia as observed in MYH9-related disorders. We used mice with megakaryocyte-restricted MYH9 inactivation to explore the role of myosin in thrombopoiesis. In situ, bone marrow MYH9Delta megakaryocytes were irregularly shaped, appearing leaky with poorly defined limits. The demarcation membranes were abnormally organized and poorly developed, pointing to an insufficient reservoir for the future formation of platelets. The cytoskeletal-rich peripheral zone was lacking due to the absence of the myosin filament network that normally surrounds the granular zone in wild-type cells. In vitro studies of cultured cells showed that MYH9Delta megakaryocytes were unable to form stress fibers upon adhesion to collagen, suggesting that the leaky shape results from defects in internal tension and anchorage to the extracellular environment. Surprisingly, the proportion of cells extending proplatelets was increased in MYH9Delta megakaryocytes and the proplatelet buds were larger. Overall, this study provides evidence for a role of myosin in different steps of megakaryocyte development through its participation in the maintenance of cell shape, formation and organization of the demarcation membranes and the peripheral zone, anchorage to the extracellular matrix, and proplatelet formation.

Inherited giant platelet disorders. Classification and literature review

Inherited giant platelet disorders are extremely rare. The aim of this article is to review the clinical and laboratory features of this heterogeneous group and to arrive at a working classification. We conducted our literature search using the National Library of Medicine database. A total of 12 clinical entities were described. We classified them into 4 groups depending on the clinical and structural abnormalities. The pathophysiology of these disorders is largely unknown, and more research is needed, particularly in the light of recent advances in laboratory medicine. This review may provide a valuable reference for clinicians and may form a basis for future classification and research.

Genetic linkage of autosomal-dominant Alport syndrome with leukocyte inclusions and macrothrombocytopenia (Fechtner syndrome) to chromosome 22q11-13

Fechtner syndrome is an autosomal-dominant variant of Alport syndrome, manifested by nephritis, sensorineural hearing loss, cataract formation, macrothrombocytopenia, and polymorphonuclear inclusion bodies. As opposed to autosomal-recessive and X-linked Alport syndromes, which have been genetically well studied, the genetic basis of Fechtner syndrome remains elusive. We have mapped the disease-causing gene to the long arm of chromosome 22 in an extended Israeli family with Fechtner syndrome plus impaired liver functions and hypercholesterolemia in some individuals. Six markers from chromosome 22q yielded a LOD score >3.00. A maximum two-point LOD score of 7.02 was obtained with the marker D22S283 at a recombination fraction of 0. Recombination analysis placed the disease-causing gene in a 5.5-Mb interval between the markers D22S284 and D22S1167. No collagen genes or genes comprising the basement membrane have been mapped to this region.

Alport syndrome. An inherited disorder of renal, ocular, and cochlear basement membranes

Alport syndrome (AS) is a genetically heterogeneous disease arising from mutations in genes coding for basement membrane type IV collagen. About 80% of AS is X-linked, due to mutations in COL4A5, the gene encoding the alpha 5 chain of type IV collagen (alpha 5[IV]). A subtype of X-linked Alport syndrome (XLAS) in which diffuse leiomyomatosis is an associated feature reflects deletion mutations involving the adjacent COL4A5 and COL4A6 genes. Most other patients have autosomal recessive Alport syndrome (ARAS) due to mutations in COL4A3 or COL4A4, which encode the alpha 3(IV) and alpha 4(IV) chains, respectively. Autosomal dominant AS has been mapped to chromosome 2 in the region of COL4A3 and COL4A4. The features of AS reflect derangements of basement membrane structure and function resulting from changes in type IV collagen expression. The primary pathologic event appears to be the loss from basement membranes of a type IV collagen network composed of alpha 3, alpha 4, and alpha 5(IV) chains. While this network is not critical for normal glomerulogenesis, its absence appears to provoke the overexpression of other extracellular matrix proteins, such as the alpha 1 and alpha 2(IV) chains, in glomerular basement membranes, leading to glomerulosclerosis. The diagnosis of AS still relies heavily on histologic studies, although routine application of molecular genetic diagnosis will probably be available in the future. Absence of epidermal basement membrane expression of alpha 5(IV) is diagnostic of XLAS, so in some cases kidney biopsy may not be necessary for diagnosis. Analysis of renal expression of alpha 3(IV)-alpha 5(IV) chains may be a useful adjunct to routine renal biopsy studies, especially when ultrastructural changes in the GBM are ambiguous. There are no specific therapies for AS. Spontaneous and engineered animal models are being used to study genetic and pharmacologic therapies. Renal transplantation for AS is usually very successful. Occasional patients develop anti-GBM nephritis of the allograft, almost always resulting in graft loss.

Giant platelet disorders in African-American children misdiagnosed as idiopathic thrombocytopenic purpura

A retrospective chart review of six African-American children with a diagnosis of macrothrombocytopenias (MTCP) was performed to evaluate the accuracy of their diagnosis. The following was diagnosed in the six children with MTCP: Fechtner syndrome (two children), Sebastian syndrome (one child), and unnamed MTCP (three children). In five families, chronic idiopathic thrombocytopenic purpura (ITP) was diagnosed in the propositus, which resulted in therapy using steroids, intravenous immunoglobulin (IVIG), and in one case splenectomy. Bleeding symptoms were generally mild. All six patients had thrombocytopenia ranging from 10 to 125 x 10(9)/L with mean platelet volume of 8 to 20 fL. Bleeding times were abnormal in two of three patients, and platelet aggregation was abnormal in three of four patients tested. Bone marrow aspirates were reported as increased megakaryocytes in the three patients on whom the procedure was performed. Ultrastructural morphology of platelets and leukocytes was performed in all six patients demonstrating giant platelets in all six patients and leukocyte inclusions in three patients. Differentiating MTCP from the more common ITP can be difficult but important in avoiding unnecessary diagnostic studies and potentially harmful therapy associated with ITP.

Sebastian syndrome: case report and review of the literature

Macrothrombocytopenias (MTCP) are a heterogeneous group of disorders associated with thrombocytopenia and giant platelets, and may include other clinical or laboratory findings such as hereditary nephritis, sensorineural deafness, leukocyte inclusions, and cataracts. Patients with MTCP may have mild to moderate bleeding symptoms or be completely asymptomatic. The most recently described MTCP is the Sebastian syndrome (SS), which consists of thrombocytopenia with giant platelets and leukocyte inclusions. Only three previous reports about this syndrome have been published. Herein, we report the first African-American family with SS. The propositus is a 4-week-old male born to a mother carrying the diagnosis of chronic idiopathic thrombocytopenia purpura (ITP). His 4-year-old brother also has thrombocytopenia. There is no history of bleeding symptoms in any of the family members. The diagnosis was established by demonstrating thrombocytopenia with giant platelets and leukocyte inclusions on both peripheral smear and by electron microscopy. This report illustrates the importance of obtaining a family history when evaluating thrombocytopenia with special emphasis on a history of thrombocytopenia, renal disease, deafness, and cataracts. It is important to differentiate between MTCP and chronic ITP to avoid the unnecessary diagnostic studies, and, more critically, unneeded and potentially harmful therapy.

Epstein's syndrome. Implications for oral surgery

Epstein's syndrome is a rare inherited disorder that appears principally as nephritis and deafness with thrombocytopathic thrombocytopenia producing a bleeding tendency. Management of the disorder for oral surgical procedures is discussed and highlighted by a case report.

Hereditary nephritis, platelet disorders and deafness-Epstein's syndrome

A 14-year-old boy with persistent proteinuria (1.6-4.0 g/day), microscopic haematuria, moderate hypertension, macrothrombocytopenia (giant platelets, platelet number 30 x 10(9)/l) and a familial sensorineural hearing loss (the father and the brother were also affected) was studied. Kidney biopsy revealed a diffuse mesangial proliferation, and a focal thickening of the glomerular basement membrane was seen on electron microscopy. A normal number of megakaryocytes was observed in bone marrow aspirates. The aggregation response of the platelets to collagen, epinephrine and adenosine diphosphate (ADP) was decreased. The platelet number was slightly diminished, platelets were of normal size in both parents and the brother, and showed a decreased aggregability in response to collagen, epinephrine and ADP in the brother and mother. No functional abnormality of the platelets was observed in the father. Urinalysis and kidney function were normal in the family members. This boy with nephritis, platelet disorders and hearing loss corresponds to Epstein's syndrome.

Epstein syndrome: oral lesions in a patient with nephropathy, deafness and thrombocytopenia

Epstein syndrome is a rare dominantly inherited disorder in which the main features are nephritis, deafness and macrothrombocytopathic thrombocytopenia. A case with oral haemorrhage and purpuric lesions is reported. This appears to be the first report of this syndrome in the dental literature.

Hereditary abnormalities of renal basement membranes

The glomerular and tubular basement membranes are the principal barriers to filtration and re-absorption of water and molecules in the nephron. They are composed primarily of type IV collagen, laminin, fibronectin, sulphated proteoglycans and collagen type I. Three common inherited diseases are associated with abnormalities of basement membrane proteins: Alport's syndrome, thin basement membrane disease (TBMD) and adult polycystic kidney disease. In this review we describe the application of molecular biological techniques to the study of these conditions. Classic Alport's syndrome is an X-linked disorder with a lamellated glomerular basement membrane (GBM) which typically results in renal failure in males. Studies with sera from patients with Goodpasture's syndrome, or monoclonal antibodies specific for the Goodpasture antigen, show that the Goodpasture antigen is absent or masked in the kidneys of individuals with Alport's syndrome. There is some evidence to suggest that the Goodpasture antigen is best represented by the non-collagenous domain of the alpha 3 chain of type IV collagen, but that other non-collagenous regions may also contribute to the antigen. It is through these non-collagenous regions that the type IV collagen chains form the typical network, and the abnormality in Alport's syndrome interferes with this network formation. However, we have recently demonstrated that the gene for the non-collagenous domain of the alpha 3 collagen chain is present in individuals with Alport's syndrome. Furthermore, other groups have shown a defect in a novel type IV collagen chain, the alpha 5 chain, in 3 unrelated cases of Alport's syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Congenital macrothrombocytopenia, leucocyte inclusions, deafness and proteinuria: functional and electron microscopic observations on platelets and megakaryocytes

We report a patient with a variant of Alport's syndrome: macrothrombocytopenia, leucocyte inclusions, deafness and proteinuria. Ultrastructural studies revealed giant spheroid platelets with a high density of organelles and a disorganized microtubular system. In addition, Fechtner inclusions were observed in neutrophils of the patient and her mother. In platelet rich plasma platelets aggregated normally for the low platelet number, although no shape change was visible. Platelet studies in whole blood using impedance aggregometry gave supernormal aggregation curves; this is not in agreement with the abnormally long bleeding time, showing the limited usefulness of this technique in patients with such large platelets. The megakaryocytes (MK) showed two different distribution patterns of the demarcation membrane system (DMS), which may explain the production of few large platelets. The formation of platelets occurred by fragmentation of the granular zone of the MKs, which seemed to be followed by expulsion of platelets through openings of the peripheral zone. The involvement of cytoskeletal structures in the organization of the DMS and the expulsion of platelets is discussed.

Fechtner syndrome: clinical and genetic aspects

Fechtner syndrome, a variant of Alport syndrome, was first reported by Peterson et al. [1985]. It is characterized by nephritis, hearing loss, eye abnormalities, macrothrombocytopenia, and leucocyte inclusions, present in varying combinations in several members of the same family. This is the second family reported; 16 relatives are affected. The clinical manifestations of the syndrome are delineated. The pattern of inheritance is autosomal dominant. The hematologic abnormalities are similar to those detected in May Hegglin anomaly. They are present in every affected relative and may be present at birth. The feasibility of prenatal diagnosis is discussed.

Epstein's syndrome: case report and survey of the literature

A diagnosis of Epstein's syndrome was made in a young female with congenital macrothrombopathic thrombocytopenia, a nephropathy and mild sensorineural deafness. Previous case reports of this rare disorder are briefly reviewed and attention is drawn to the frequent association between inherited thrombocytopenia and renal disease.

Successful renal transplantation for Epstein syndrome

Successful cadaveric renal transplantation was accomplished in a patient with Epstein syndrome, a triad of macrothrombocytopenia, partial high-frequency hearing loss, and nephritis, which often progresses to complete renal failure. The success of the transplant demonstrates that the macrothrombocytopenia which occurs in this syndrome is not a contraindication to aggressive management of end-stage renal disease.

Hereditary macrothrombocytopathia, deafness and nephritis (Epstein's triad)

Epstein's triad is a syndrome with a combination of hereditary macrothrombocytopathia and progressive sensorineural hearing loss and nephritis. This syndrome is rare and may be inherited as dominant trait or sex-linked or new mutation. But the true mode of this syndrome is still questionable. Bilateral sensorineural hearing loss is progressive and seems not to be related to the severity of bleeding episodes and renal failure. An 8-year-old boy with these findings is presented and discussed in this article.