Vitamin D Metabolism Genes in Asthma and Atopy.

Asthma and allergy are complex diseases influenced by poorly understood environmental and genetic factors. The innate and adaptive immune systems play an important role in the pathogenesis of these diseases. Many genes involved in inflammation and immunoregulation pathways have been related to asthma and allergy susceptibility. Among the diverse extra-skeletal actions of vitamin D, growing evidence indicates that vitamin D is an important modulator of the immune system response and may influence the development of asthma and allergy susceptibility through different mechanisms. The vitamin D pathway is under the control of a set of polymorphic genes that code for key enzymes which regulate the synthesis and metabolism of vitamin D (i.e. CYP27A1, GC, CYP27B1 and CYP24A1) and of genes that encode for downstream mediators of vitamin D signalling (i.e. VDR, RXR, PPAR, NCOA and SMAD). This metabolism gene pathway is of fundamental importance in regulating vitamin D availability and biological response. Unravelling the role of vitamin D metabolism genes on asthma and atopy susceptibility may help to understand the impact of vitamin D on the development of these disorders. This review article aims: 1) to describe the genetics of the vitamin D pathway, 2) to revise the potential mechanisms by which vitamin D pathway genes may affect the immune and respiratory systems predisposing to asthma and allergy disorders; and 3) to summarize the influence of genetic variation on vitamin D pathway genes on the development of asthma and allergy.