SMPD1 and hereditary disease: Niemann–Pick is a genetic disorder with autosomal recessive inheritance that is caused by mutations in the NPC1 gene on chromosome 18q11 (OMIM #257220), by mutations in the NPC2 gene on chromosome 14q24 (OMIM #607616), and by mutations in the sphingomyelin phosphodiesterase-1 (SMPD1) gene on chromosome 11p15 (OMIM #257200).