Niemann-Pick disease is caused by a deficiency in the enzyme sphingomyelinase with an accumulation of unmetabolized lipid sphingomyelin and cholesterol. This material accumulates in histiocytes which populate the spleen, liver, bone marrow, and lymph nodes.
There are five types of Niemann-Pick disease (A-E). Types A and B make up more than 95% of all Niemann-Pick disease and further discussion will be limited to these two types.
Type A is known as the classic Niemann-Pick disease. It presents early in infancy with difficulty feeding, failure to thrive, and retarded physical and mental development. The skin often has a waxy consistency and the patient may be jaundiced with hepatosplenomegaly. Death occurs between one and two years.
Type B presents with hepatosplenomegaly noted in infancy, but without neurologic symptoms. Individuals live longer than Type A, but usually die in late childhood to early adolescence. There is no effective therapy at this time.