A new variant of sphingomyelinase deficiency (Niemann-Pick): visceromegaly, minimal neurological lesions and low in vivo degradation rate of sphingomyelin.

Three males (aged 10 years, 3 years 9 months and 2 years 8 months) with profound sphingomyelinase deficiency are presented. The sphingomyelin storage in the liver biopsies attained 30-fold, 65-fold and 16-fold increases against controls, respectively. Levels of bis(monoacylglyceryl) phosphate were also increased. In two cases the bone marrow contained foam cells with liquid crystals of sphingomyelin. Besides the visceral involvement dominated by hepatosplenomegaly, all three cases showed discrete, so far stationary (8 years, 42 months and 28 months) neuropathic features and retinal lesions resembling the classical cherry-red spot. Electrophysiological examinations showed a variable reduction of peripheral nerve conduction velocity and prolongation of the latencies of somatosensory, visual and auditory evoked potentials. Ultrastructural examination of skin nerves showed a slight storage, mainly in Schwann cells. In some myelinated fibres there were pseudomyelinic ovoids. The cases therefore displayed features of both A and B types of sphingomyelinase deficiency and should be conventionally classified as intermediate. However, the very low levels of in vivo sphingomyelin hydrolysis (not exceeding 6%, against 30 +/- 10% in type B and 77 +/- 5% in controls) were clearly within the range of type A values (5 +/- 2%). Accordingly, we suggest that the cases may be biochemically classified as variants of type A disease.