Hematopoietic KIT D816Y mutation presenting as in utero aggressive systemic mastocytosis with response to midostaurin.

A Black female was born at 38 weeks to nonconsanguineous parents, with pregnancy complicated by intrauterine growth restriction and breech presentation requiring Cesarean delivery. At birth, she was small for gestational age at 2260 g and had prominent skin findings with diffuse, red-brown indurated nodules and plaques with overlying blisters, erosions, and dyschromia (Figure 1). A protuberant abdomen with marked hepatosplenomegaly and diffuse adenopathy were also noted. Initial laboratory evaluation revealed thrombocytopenia (119,000), direct hyperbilirubinemia (1.4 mg/dL), elevated alkaline phosphatase (67 units/L), and elevated gamma glutamyl transpeptidase (GGT, 231 units/L).