Vitamin D receptor gene polymorphisms and Parkinson's disease in a population with high ultraviolet radiation exposure

INTRODUCTION: A high prevalence of vitamin D deficiency has been reported in Parkinson's disease (PD). Epidemiologic studies examining variability in genes involved in vitamin D metabolism have not taken into account level of exposure to ultraviolet radiation (UVR). We examined whether exposure to UVR (as a surrogate for vitamin D levels) and variations in the vitamin D receptor gene (VDR) are associated with PD.

METHODS: Within a geographical information system (GIS) we linked participants' geocoded residential address data to ground level UV data to estimate historical exposure to UVR. Six SNPs in VDR were genotyped in non-Hispanic Caucasian subjects.

RESULTS: Average lifetime UVR exposure levels were >5000 Wh/m(2), which was higher than levels for populations in previous studies, and UVR exposure did not differ between cases and controls. Homozygotes for the rs731236 TT (major allele) genotype had a 31% lower risk of PD risk (OR=0.69; 95% CI=0.49, 0.98; p=0.04 for TT vs. TC+CC). The rs7975232 GG (minor allele) genotype was also associated with decreased risk of PD (OR=0.63; 95% CI=0.42, 0.93; p=0.02 for GG vs. TG+TT). The association between PD risk and a third locus, rs1544410 (BsmI), was not statistically significant after adjustment for covariates, although there was a trend for lower risk with the GG genotype.

CONCLUSIONS: This study provides initial evidence that VDR polymorphisms may modulate risk of PD in a population highly exposed to UVR throughout lifetime.