R542X mutation in SMPD1 gene: genetically novel mutation with phenotypic features intermediate between type A and type B Niemann-Pick disease.

Niemann-Pick disease (NPD) is a heterogenous group of progressive neurovisceral disorder characterised by lysosomal accumulation of sphingomyelin. NPD types A and B are caused by mutations involving sphingomyelin-phosphodiesterase-1 (SMPD1) gene and are characterised by deficiency of acid sphingomyelinase activity. We present a case of a 9-month infant with clinical manifestations intermediate between types A and B NPD and genetically illustrating a novel R542X mutation in the exon 6 of SMPD1.