GC and attention deficit-hyperactivity disorder: However, the leave-one-out analysis showed that the exclusion of SNP rs3755967 (GC: group-specific component gene, GC protein is a major vitamin D-binding protein in plasma [35]) would lead to a significant overall positive effect of 25(OH)D on ADHD, i.e. higher 25(OH)D levels would cause higher ADHD risk (Figure S2).