Acid sphingomyelinase deficiency (ASMD), due to mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene, was historically divided into two phenotypes: Niemann-Pick disease type A (OMIM 257200) – a neuronopathic, rapidly progressing and fatal disorder, and Niemann-Pick disease type B (OMIM 607616) – a non-neuronopathic, slowly progressive, visceral disorder [1, 2]. The gene discussed is SMPD1; the disease is acid sphingomyelinase deficiency.