Thrombin generation in two families with MYH9-related platelet disorder

MYH9-related platelet disorders are inherited macrothrombocytopenias with additional clinical manifestations including renal failure, hearing loss, pre-senile cataract, and inclusion bodies in leucocytes that are present in different combinations. The MYH9 gene codes for the cytoplasmic contractile protein non-muscular myosin heavy chain IIA, present in several tissues. The bleeding tendency is usually mild to moderate but rarely, thrombotic complications are also seen. We report on the thrombin generation potential (ETP) in patients with MYH9-related disease with and without arterial thrombosis. In family A, four affected members [c.5521G>A mutation causing p.(Glu1841Lys)] were evaluated. Three of them had a moderate bleeding tendency and in two renal insufficiency and hearing loss were already present. These two patients had an arterial thrombosis (myocardial infarction and pons infarction, respectively) before 50 years of age. In family B, two members were affected [c.4679T>G, resulting in p.(Val1560Gly)]. Their bleeding tendency was mild (bleeding scores 4 and 3, respectively). Thrombelastography (ROTEM) was normal in all six individuals. ETP was below the normal range in family B. However, in family A, the two members affected by thrombosis had a normal ETP, indicating that other factors compensated for the low platelet count and might have contributed to the arterial thrombosis.