Because of these findings and the observed transcriptional regulation of Cyp11a1 by VDR in mice, a combined analysis of SNPs in CYP11A1 and VDR is performed to further determine if an epistatic phenomenon, here defined as the effect of one locus being dependent on the genotype of a second locus, may be involved in the development of childhood asthma. The gene discussed is CYP11A1; the disease is childhood onset asthma.