The aforementioned large Mendelian randomisation study [35] investigated four single nucleotide polymorphisms (SNPs) influencing 25(OH)D transport (GC globulin (vitamin D-binding protein)), synthesis (7-dehydrocholesterol reductase), hepatic hydroxylation (CYP2R1), and catabolism (CYP24A1), to estimate the association of genetically determined 25(OH)D and the risk of asthma. This evidence concerns the gene CYP2R1 and asthma.