Like Gaucher's disease, Niemann-Pick disease is a lysosomal storage disorder in which a missing enzyme prevents the metabolism of a certain compound that then accumulates in the cells.
There are three types of this disease:
- Type A is a genetic disorder in which sphyingomyelin (ceramide phosphorylcholine) accumulates in cells of infants and young children. This condition causes the liver and the spleen to become enlarged and the child not to thrive. There is rapid degeneration of the nerves that leads to death by age two or three.
- Type B, like type A, is a genetic disorder in which sphyingomyelin accumulates in cells. A patient may develop fatty, irregular yellow patches or nodules on the skin of the eyelids, neck or back that is associated with disturbances in cholesterol metabolism. A patient may also have skin discoloration and enlarged liver, spleen and lymph nodes. However, persons with type B have little or no nerve involvement and survive into adulthood.
- Type C is caused by an error in cholesterol metabolism that results in unesterified cholesterol accumulating in cells. Its symptoms include variable enlargement of the liver and spleen, an increasing inability to control muscle movement, seizures, disordered muscle tone, dementia and sometimes fatal neonatal liver disease. It usually appears in late childhood with death in the patient's 20s. When it appears in adulthood it can produce psychosis and dementia.
Causes and Risk Factors
Types A and B are inherited conditions that most often appear in Jewish families. Type C is not inherited and appears in all ethnic groups.
Type B is usually diagnosed in childhood because of the enlarged liver and spleen. A tissue biopsy should be done in types A and B and diagnosis confirmed by tests to show whether the enzyme acid sphingomyelinase is present.
Prenatal diagnosis for types A and B is done by or Diagnosis of type C requires a series of laboratory tests to confirm its presence.
Treatment of all types is supportive and nonspecific.