We aimed to examine associations among serum 25-hydroxyvitamin D levels, 1,25-dihyroxyvitamin D levels, vitamin D receptor polymorphisms, vitamin D binding protein gene polymorphisms, and the severity of Parkinson's disease. In 137 patients, the severity of Parkinson's disease was evaluated using Hoehn & Yahr stage and Unified Parkinson's Disease Rating Stage by neurologists and compared with 25-hydroxyvitamin D, 1,25-hydroxyvitamin D, vitamin D receptor polymorphisms, ie, FokI (rs10735810), BsmI (rs1544410), Cdx2 (rs11568820), ApaI (rs7976091), and TaqI (rs731236), and vitamin D binding protein gene polymorphisms GC1 (rs7041)/GC2 (rs4588) in a cross-sectional study. Mean ± standard deviation levels of 25-hydroxyvitamin D were 21.1 ± 9.0 ng/mL. Levels were deficient (<20 ng/mL) in 49% of patients. In contrast, 1,25-hydroxyvitamin D levels were considered normal in all patients. Higher circulating 25-hydroxyvitamin D levels were significantly associated with milder Parkinson's disease evaluated by Hoehn & Yahr stage (P = .002) and total Unified Parkinson's Disease Rating Stage (P = .004) even after multivariate adjustment for 8 covariates, including disease duration. However, significant associations were not observed in 1,25-hydroxyvitamin D levels. Under multivariate analysis with 25-hydroxyvitamin D as well as other 8 covariates including disease duration, carriers of vitamin D receptor FokICC genotype had a milder form of Parkinson's disease: odds ratio, 0.32; 95% confidence interval, 0.16 to 0.66, P = 0.002. These results suggest that higher 25-hydroxyvitamin D levels and the vitamin D receptor FokICC genotype may be independently associated with milder forms of Parkinson's disease. However, significant associations were not observed in 1,25-hydroxyvitamin D levels.
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