Traditionally, “familial HLH” (FHL) has been defined as a genetic disease, in which the predisposition to HLH is the dominant feature (PERFORIN deficiency, MUNC13-4 deficiency, SYNTAXIN-11 deficiency, and MUNC18-2 deficiency) (12–17), while “immunodeficiencies with albinism” (Chediak–Higashi syndrome (CHS) or LYST deficiency, Griscelli syndrome type 2 (GS2) or RAB27A deficiency, and Hermansky–Pudlak syndrome type 2 (HPS2) or AP3b1 deficiency) (18–22) combine this predisposition with clinical manifestations of albinism and variable degrees of other immune cell and platelet dysfunction (23–28). The gene discussed is UNC13D; the disease is hyperinsulinemic hypoglycemia, familial, 4.