Genetics of Obstructive Sleep Apnea: Vitamin D Receptor Gene Variation Affects Both Vitamin D Serum Concentration and Disease Susceptibility

Obstructive sleep apnea syndrome (OSAS) is a multifactorial and common disorder affecting 10-17% of men and 3-9% of women. A low vitamin D serum concentration has been reportedly linked to OSAS susceptibility, but the underlying molecular genetic mechanisms are poorly understood thus far. We report here original findings on the ways in which vitamin D receptor (VDR) gene polymorphic variation (FokI, BsmI, ApaI, and TaqI polymorphisms) impacts serum vitamin D concentration and, additionally, susceptibility to OSAS. In a sample of 176 consecutive subjects (144 patients with OSAS and 32 healthy controls) phenotyped by full polysomnography (PSG), we characterized human genetic variation in VDR using the Sequenom MassARRAY iPLEX platform. A logistic regression analysis was employed to account and correct for covariates such as sex, age, body mass index, and comorbidities. Importantly, we observed that the FokI CC genotype frequency was markedly higher in patients with OSAS compared with controls (50.7% vs. 28.1%; p = 0.027). VDR FokI polymorphism explained 14.5% of vitamin D serum concentration variability. Moreover, the VDR FokI polymorphism was also associated with excessive daytime sleepiness (p = 0.016). To the best of our knowledge, this is the first clinical genetics study examining the role of VDR polymorphic variation on OSAS as phenotyped using full PSG. We call for further studies of vitamin D-related mechanisms that might contribute to OSAS risk in independent populations.