NPD comprises three different pathologies, namely NPD type A, B, and C. NPD type A and B are now most commonly categorized as acid sphingomyelinase deficiencies (ASMDs), as they are caused by mutations in the gene SMPD1, which codes for sphingomyelin phosphodiesterase 1. This evidence concerns the gene SMPD1 and hyperinsulinemic hypoglycemia, familial, 4.