In Niemann-Pick disease, harmful quantities of a fatty substance accumulate in the spleen, liver, lungs, bone marrow and sometimes in the brain. There are two types of Niemann-Pick disease, type A and type B. Type A is more common in the Ashkenazi Jewish population, with an estimated one in 90 carrier frequency. The gene is located on chromosome 11.

Individuals with Niemann-Pick disease lack a substance called acid sphingomyelinase (ASM). ASM usually breaks down a substance in the body called sphingomyelin. If ASM is missing from the body, sphingomyelin builds up in certain cells and causes damage to the central nervous system, liver and lungs. Children with Niemann-Pick disease usually appear normal at birth. The first signs of the disease appear at about three to five months of age. Progressive loss of early motor skills, feeding difficulties, and a large abdomen occur at this time. These children usually do not live past two to three years of age.