APA Dictionary of Psychology

an inherited group of lipid-storage disorders generally marked by a deficiency of the enzyme acid sphingomyelinase and accumulation of lipids in brain tissue and visceral organs. Massive liver and spleen enlargement (hepatomegaly and splenomegaly) may occur. In Type A, progressive deterioration of the nervous system, blindness, and death before adulthood are common. In Type B, the nervous system is not affected and individuals may live into adulthood. Types C1 and C2 usually appear in childhood but can appear in infancy or adulthood. They are characterized by severe liver disease, jaundice, breathing difficulties, developmental delay, seizures, poor muscle tone, lack of coordination, problems with feeding, and an inability to move the eyes vertically. Type A occurs more frequently among individuals of Ashkenazi (eastern and central European) Jewish descent and is caused by mutations in the SMPD1 gene, whereas Type C1 occurs more frequently in people of French-Acadian descent in Nova Scotia and is caused by mutations in the NPC1 gene. Also called sphingomyelin lipidosis. See also lipid-metabolism disorders. [Albert Niemann (1880–1921) and Ludwig Pick (1868–1944), German physicians]