Clinical Characteristics of Autosomal Dominat Giant Platelet Syndromes (GPS) and Mutation Analysis of MYH9 Encoding Non-Muscle Myosin Heavy Chain from 6 Unrelated Korean Patients.

Autosomal dominant GPS is characterized by thrombocytopenia, giant platelets and Doehle-like inclusion bodies. Studies have indicated that platelet structure and function are normal, suggesting a defect in megakaryocyte fragmentation. This study was aimed to identify Korean patients with GPS and define clinical findings and molecular characteristics on them. Twenty-two patients from 6 unrelated families were identified. Giant platelets, measuring greater than red cells on blood smear were found to be 3.1% (1–11%). The median platelet count was 61,000/μL. Doehle-like inclusion bodies were found in 4 families, while renal impairment in 2. MYH9 in each family was analyzed by direct sequencing of exons or cDNAs. Among 6 families, 5 families were found to have the mutations: Arg1933Ter, Trp33Cys, Lys373Asn, Ile1816Val, Arg1165Cys located in 41st, 2nd, 11th, 38th, 27th exons, respectively. All of the mutations are found only in the affected patients, but not in the normal siblings. Arg1933Ter and Lys373Asn were reportedly associated with GPS and Arg1933Ter is known to make the protein unstable. The novel mutations, Trp33Cys and Ile1816Val, were placed in highly conserved amino acids in mammals and Drosophila, and even in other types of myosin heavy chain. Computer-aided modeling analysis shows that Trp33Cys is located in the proximal portion of the myosin head, serving as a dock for actin binding, while Ile1816Val is in the distal portion of myosin tail, which may act to form polymer with other myosin heavy chains. Isolated mononuclear cells or the stable cell lines originated from Trp33Cys, Lys373Asn and Arg1165Cys patients were subjected to immunoblot. Compared to their normal siblings, the 220 kDa bands in the soluble fraction were decreased in those patients, while the bands were increased in the insoluble pellet. However, Northern blot analysis revealed that transcript levels were not altered in the samples from patients. Trp33Cys, Lys373Asn, and Arg1165Cys also produced aberrant 140 kDa bands in addition to normal 220 kDa MYH9 band in the insoluble fractions. After immunoprecipitation with MYH9 antibody, the 140 kDa bands were analyzed and turned to be actinin. These results suggest that novel mutations found in GPS are directly associated with the disease and that the phenotype might be caused by the solubility or instability of the proteins.