MYH9-related disease (MYH9-RD) is characterized in all affected individuals by hematologic features present from birth consisting of platelet macrocytosis (i.e., >40% of platelets larger than 3.9 µm in diameter), thrombocytopenia (platelet count <150 x 109/L), and aggregates of the MYH9 protein in the cytoplasm of neutrophil granulocytes. Most affected individuals develop one or more additional extrahematologic manifestations of the disease over their lifetime, including sensorineural hearing loss, renal disease (manifesting initially as glomerular nephropathy), presenile cataracts, and/or elevation of liver enzymes.