While homozygous pathogenic mutations in the
NPC1gene cause Niemann-Pick type C1 disease, heterozygous mutations cause highly-penetrant obesity. We aimed to investigate the prevalence of NPC1mutations and their signatures of natural selection in 122,678 exome sequenced participants from six ethnic groups in the Genome Aggregation Database. Pathogenic missense coding mutations were identified by in silico tools and the ClinVar database. Signatures of natural selection were assessed by the probability of NPC1being loss-of-function mutation intolerant and Z-scores of observed/expected synonymous and non-synonymous mutation ratios. There was no evidence of negative selection observed for synonymous, non-synonymous and loss-of-function mutations. However, there were significant ethnic differences in the prevalence of heterozygous pathogenic NPC1mutations ranging from 0.56% in Ashkenazi Jewish to 3.26% in African/African Americans (5.8-fold difference). Four homozygous carriers of pathogenic NPC1mutations were also identified, belonging to the South Asian population. In conclusion, NPC1mutations are consistent with a model of balanced selection, where heterozygotes and homozygotes have higher and lower reproductive fitness, respectively. Therefore, NPC1heterozygous mutations may account for a substantial and ethnic-dependent percentage of obesity in the general population, while NPC1homozygous mutations may be frequent in the South Asian populations and warrants more investigation.