Niemann-Pick disease types A and B result from deficient activity of acid sphingomyelinase, encoded by a gene on chromosome 11. The defect results in accumulation of sphingomyelin in the monocyte-macrophage system. The progressive deposition of sphingomyelin in the central nervous system leads to type A, and in nonneuronal tissues leads to type B. Type C is a neuropathic form that results from the defective cholesterol transport.
Depending on the type, Niemann-Pick disease has classic signs, including:
• Cherry red spot in macula
• Psychomotor deterioration
• Reticular pulmonary infiltrates
• Foamy cells in the bone marrow
Table 5-8 lists the clinical features of the different types of Niemann-Pick disease. Diagnosis
Diagnosis involves examining leukocytes or cultured fibroblasts to determine sphin-gomyelinase activity.
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