Myosin Heavy Chain 9 (MYH9)-Related Congenital Macrothrombocytopenia

Myosin heavy chain 9 (MYH9)-related hereditary macrothrombocytopenia is caused by mutation of the MYH9 gene encoding the heavy chain A of non-muscle myosin of class II. We present a case that emphasizes the importance of awareness of rare disorders which could potentially avoid over-investigation, especially in benign conditions. A 72-year-old Caucasian female presented for preoperative evaluation for cataract extraction. She was noted to have thrombocytopenia of 30 K/uL along with elevated creatinine. She denied any acute symptoms except for a prolonged history of easy bruising. Physical exam revealed bruising over the extremities. Upon further questioning, she was previously investigated for thrombocytopenia and had multiple diagnostic as well as therapeutic interventions including bone marrow biopsies, steroids, intravenous immunoglobulins with no improvement. Her family history is consistent with low platelet counts for at least three generations. Peripheral blood smear showed large platelets, normal red and white blood cells with Döhle bodies. Further genetic testing revealed an inherited MYH9 mutation which is autosomal dominant. MYH9-related disorders are characterized by macrothrombocytopenia, often associated with glomerulonephritis, sensorineural deafness, cataracts, and cytoplasmic inclusion bodies within leukocytes. Management is mainly conservative and directed towards the prevention of iron deficiency anemia in young females. The use of desmopressin, in combination with tranexamic acid, is recommended in a perioperative setting. Our case emphasizes the importance of history-taking skills that could potentially minimize further diagnostic or therapeutic interventions in this benign genetic disorder.