Aim To assess the frequency of low vitamin D deficiency and conduct an association search for genetic variants (c.1206T>C, c.152T>C, c.1174+283G>A) of the VDR gene with clinical manifestations, calcidiol levels and response to therapy in cystic fibrosis ( CF), bronchial asthma (BA), juvenile idiopathic arthritis (JIA).

Material and Method 283 patients with cystic fibrosis (CF), 160 with BA, 150 with JIA and 333 healthy children in the control group were examined, and calcidiol content was determined. Testing of polymorphic variants of the VDR gene (c.1206T>C, c.1175–9G>T, c.152T>C, c.1174+283G>A) was carried out using PCR and RFLP analysis.

Results A year-round high incidence of low vitamin D supply was revealed among CF in 50.7%, asthma in 89.6%, and JIA in 74.0%. The occurrence of meconium ileus, decreased lung function, chronic Ps. aeruginosa infection, a chronic lung infection caused by non-fermenting gram-negative bacteria, is higher among carriers of the TT c.152T>C FokI VDR gene genotype in cystic fibrosis. Liver cirrhosis is more often (OR=4.300; p=0.051) realized in carriers of the AA genotype BsmlI (c.1174+283G>A) of the VDR gene. The occurrence of manifestations of the ‘atopic march’ increases many times when carrying the genotype TT c.1206T>C(A>G) TaqI (OR=13.000; p=0.046), genotypes AA and GA BsmlI (c.1174+283G>A) (OR= 18.000; p=0.017). Calcidiol deficiency against the background of asthma is 2.7 times (p = 0.003) more often recorded among carriers of the TT and CT genotypes c.1206T>C(A>G) TaqI of the VDR gene. The risk of systemic onset of JIA, polyarticular variant, high degree of activity, uveitis, high frequency of biological therapy (p <0.05) are carriers of the TT genotype c.1206T>C(A>G) TaqI, TT genotype c.152T>C FokI, genotype AA polymorphism BsmlI (c.1174+283G>A) of the VDR gene.

Conclusions The high frequency of low vitamin D supply, the contribution of VDR gene polymorphisms during the studied diseases and vitamin D supply are shown.