Chronic Niemann-Pick disease with sphingomyelinase deficiency in two brothers with mental retardation.

Clinical, biochemical, and electron microscopic studies are presented in two brothers with Niemann-Pick disease. The clinical features include hepatosplenomegaly and mental retardation without any other neurological signs. Roentgenograms of the chest showed bilateral diffuse reticular infiltration. The amounts of sphingomyelin and cholesterol in liver were increased, and sphingomyelinase activities in both liver and skin fibroblasts were markedly reduced in Case 1. Numerous foam cells and myelin figures were observed in the liver, kidneys, bone marrow, and lymph nodes on electron microscopical examination. These cases were regarded as a variant of Niemann-Pick disease from our investigations as they have mental retardation as an exceptional symptom when they are diagnosed as type B.