Niemann-Pick disease type C: spectrum of HE1 mutations and genotype/phenotype correlations in the NPC2 group

Abstract

In Niemann-Pick disease type C (NPC), a genetic heterogeneity with two complementation groups--NPC1, comprising > or =95% of the families, and NPC2--has been demonstrated. Mutations in the NPC1 gene have now been well characterized. HE1 was recently identified as the gene underlying the very rare NPC2. Here we report the first comprehensive study of eight unrelated families with NPC2, originating from France, Algeria, Italy, Germany, the Czech Republic, and Turkey. These cases represent essentially all patients with NPC2 who have been reported in the literature, as well as those known to us. All 16 mutant alleles were identified, but only five different mutations, all with a severe impact on the protein, were found; these five mutations were as follows: two nonsense mutations (E20X and E118X), a 1-bp deletion (27delG), a splice mutation (IVS2+5G-->A), and a missense mutation (S67P) resulting in reduced amounts of abnormal HE1 protein. E20X, with an overall allele frequency of 56%, was established as the common mutant allele. Prenatal diagnosis was achieved by mutation analysis of an uncultured chorionic-villus sample. All mutations except 27delG were observed in a homozygous state, allowing genotype/phenotype correlations. In seven families (with E20X, E118X, S67P, and E20X/27delG mutations), patients suffered a severe and rapid disease course, with age at death being 6 mo-4 years. A remarkable feature was the pronounced lung involvement, leading, in six patients, to early death caused by respiratory failure. Two patients also developed a severe neurological disease with onset during infancy. Conversely, the splice mutation corresponded to a very different clinical presentation, with juvenile onset of neurological symptoms and prolonged survival. This mutation generated multiple transcripts, including a minute proportion of normally spliced RNA, which may explain the milder phenotype.

Figure 1

Multiple abnormal HE1/NPC2 mRNAs in patient 8—PAGE analysis of RT-PCR products and schematic representations of samples of HE1/NPC2 cDNA isolated from the patient’s fibroblasts.

Figure 2

Western blot of HE1/NPC2 in cultured fibroblasts from three patients with NPC2 and from one normal subject. The patients with NPC2 were homozygous for the indicated mutations.

Figure 3

Restriction analysis of E20X. E20X creates a StuI restriction site. For families 1, 3, and 6 (tables 1 and 3), besides the proband (P) or affected fetuses (f), the study included the father (F) and the mother (M). Lane P5 corresponds to case 5. Probands with other HE1/NPC2 mutations (cases 8 and 4 [lanes P8 and P4, respectively]) showed a normal pattern and served as controls.