Niemann-Pick disease is a sphingolipidosis, an inherited disorder of metabolism, caused by deficient sphingomyelinase activity, resulting in accumulation of sphingomyelin (ceramide phosphorylcholine) in reticuloendothelial cells.
Niemann-Pick disease inheritance is autosomal recessive and appears most often in Ashkenazi Jews; 2 types, A and B, exist. Type C Niemann-Pick disease is an unrelated enzymatic defect involving abnormal cholesterol storage.
Children with type A have < 5% of normal sphingomyelinase activity. The disease is characterized by hepatosplenomegaly, failure to thrive, and rapidly progressive neurodegeneration. Death occurs by age 2 or 3 yr.
Patients with type B have sphingomyelinase activity within 5 to 10% of normal. Type B is more variable clinically than type A. Hepatosplenomegaly and lymphadenopathy may occur. Pancytopenia is common. Most patients with type B have little or no neurologic involvement and survive into adulthood; they may be clinically indistinguishable from those with type I Gaucher disease. In severe cases of type B, progressive pulmonary infiltrates cause major complications.
Both types are usually suspected by history and examination, most notably hepatosplenomegaly. Diagnosis of Niemann-Pick disease can be confirmed by sphingomyelinase assay on WBCs and can be made prenatally by using amniocentesis or chorionic villus sampling. DNA tests can be done to diagnose carriers. (Also see testing for suspected inherited disorders of metabolism.)