Highly variable neural involvement in sphingomyelinase-deficient Niemann-Pick disease caused by an ancestral Gypsy mutation.

Niemann-Pick disease (NPD), an autosomal recessive disorder resulting from mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene, is subdivided into the acute, lethal neuronopathic type A, and the chronic visceral type B, explained by the different residual activity levels of acid sphingomyelinase (ASMase). An increasing number of reports on intermediate forms, challenging this traditional clinical classification, have described a broad range of neurological manifestations; however genotype-phenotype correlations have been compromised by relatively small sample sizes and/or allelic heterogeneity. Here we present a genetically homogeneous group of 20 Gypsy patients with intermediate NPD, where we observed a surprising diversity of neurological features.