Niemann Pick Disease

Niemann-Pick disease, types A and B, are systemic lipi-doses caused by a deficiency of the enzyme acid sphin-

gomyelinase, encoded by a gene on chromosome 11. As a result, sphingomyelin accumulates in the neurons and visceral organs in type A, and only in the viscera in type B. Type A occurs in Ashkenazi Jewish population and affects chiefly children. A macular cherry red spot may be present. Foam cells are found in the bone marrow, and vacuolated lymphocytes are found in blood. The clinical course averages from 1 to 3 years.

Pathology: Grossly, the brain is atrophic. Histologi-cally, ballooned neurons contain sphingomyelin, which in frozen sections stains positively for lipids and weakly with PAS (Fig. 9.3). Systemic pathology is characterized by the presence of foamy microphages in the liver, spleen, lung, lymph nodes, and bone marrow.

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