Transitory type of sphingomyelinase deficient Niemann-Pick disease: clinical and morphological studies and follow-up of two sisters.

The transitory type is a rare and ill-defined variant of sphingomyelinase deficient NPD. Here reported are full clinical and morphological studies on two sisters with the transitory type. Our cases have the following features in common: 1) prominent visceral involvement from early infancy, such as marked hepatosplenomegaly, pulmonary infiltration, and numerous characteristic foam cells in the bone marrow aspirates; 2) very low sphingomyelinase activities in cultured skin fibroblasts; 3) atypical cherry-red spots in the retina; despite 4) absence of any neurological symptoms even at the age of 5 years and 6 months, and 3 years and 9 months, respectively.