Niemann-Pick disease. Light micrograph of a section through bone marrow from a patient with Niemann-Pick disease. This is an inherited metabolic disorder in which a fatty substance called sphingomyelin accumulates in the spleen, lungs, liver and bone marrow, and sometimes the brain. This is due to an absence of the enzyme sphingomyelinase. The disease may appear in infancy, where it is usually fatal within 18 months, or later in childhood. It causes enlargement of the affected organs, weak and painful bones and sleep disorders. Some forms also cause severe nervous system damage. There is no cure, treatment is aimed at improving quality of life.