Buchbinder D, Steward CG, Puthenveetil G, Nugent D, Hsieh L, Kirov I, Neudorf S, Soni A. Successful cord blood transplantation in a patient with malignant infantile osteopetrosis and hemophilia. Abstract: MIOP is a congenital disorder of osteoclast differentiation or dysfunction. Inadequate bone resorption by osteoclasts results in a spectrum of complications including hypocalcemia, osteosclerosis, marrow failure, extramedullary hematopoiesis, hydrocephalus, visual deficits, and eventual mortality. Early diagnosis and timely HCT is a recommended treatment approach for select patients prior to the development of end-organ damage. A comorbid bleeding disorder presents a unique challenge in the setting of MIOP and cord blood HCT given the additional risk factors for bleeding including delayed engraftment, a high risk of developing sinusoidal obstruction syndrome, and potential need for emergent invasive procedures. To our knowledge, this is the first report of a patient with an autosomal recessive form of MIOP who successfully underwent a cord blood HCT complicated by the presence of mild hemophilia A and HCT-related complications including delayed engraftment, sinusoidal obstruction syndrome, and need for multiple invasive procedures (e.g., ventriculostomy, tracheostomy) without clinically significant bleeding. Given the underlying diagnosis of MIOP and need for HCT, the challenge of mitigating the significant risk of bleeding in a patient with a comorbid bleeding disorder is discussed.