<b><i>DIAPH1</i></b> Mutation as a Novel Cause of Autosomal Dominant Macrothrombocytopenia and Hearing Loss

Macrothrombocytopenia (MTP) is a group of rare disorders characterized by giant platelets, thrombocytopenia, and variable association with abnormal bleeding. Inherited MTP are frequently misdiagnosed as immune thrombocytopenia. Associated second-organ manifestation can help narrow down syndromic MTPs. We describe a case of autosomal dominant sensorineural hearing loss and MTP caused by a gain of function mutation in DIAPH1 . This mutation causes altered megarkaryopoiesis and platelet cytoskeletal deregulation. Although hearing loss and MTP were likely progressive, clinically significant bleeding was not observed. DIAPH1 -related MTP can be distinguished clinically from MYH9 mutation by the absence of cataracts and glomerular disease.