Epstein syndrome is one form of the ``MYH9 syndrome'' (a group that includes four clinical forms with similar manifestations: May-Hegglin anomaly, Sebastian syndrome, Fechtner syndrome, and Epstein syndrome; see these terms), characterized by usually severe macrothrombocytopenia but paradoxically resulting in few if any symptoms. The prevalence of Epstein syndrome is unknown. Less than 100 families have been described so far. Macrothrombocytopenia is defined as the presence of giant platelets, with a diameter equal to or greater than that of a red blood cell. Epstein syndrome clinically resembles Fechtner syndrome (renal involvement marked by interstitial glomerulonephritis and sensorineural deafness associated with thrombopenia), but it can be distinguished by the absence of cataract. Epstein syndrome is transmitted following an autosomal dominant pattern, most often as a result of point mutations in the MYH9 gene. This gene, localized to 22q12-13, encodes the nonmuscle myosin heavy chain type IIA (MYHIIA), which is expressed in some blood cells (polynuclear cells, monocytes and platelets), in the cochlea and in the kidneys. These molecular anomalies result in abnormal dimerization of the MYHIIA protein, which becomes unstable and coprecipitates with normal MYHIIA in the cytoplasm of leucocytes, thus forming cytoplasmic inclusion bodies that are absent in Epstein syndrome. This abnormal dimerization also leads to failure to properly organize the cytoskeleton in megakaryocytes, which triggers macrocytic thrombopenia. Glomerular involvement occurs later and inconstantly as the dimerization defect of MYHIIA could be compensated in situ by the presence of another myosin type (type IIB). The majority of patients do not suffer from abnormal bleeding and in this case no specific treatment is required. However, platelet transfusion may be advised before a surgical operation. The management of nephropathy depends on the degree of renal involvement: from regular medical surveillance to renal dialysis.
Last update: October 2006