GC and early-onset autosomal dominant Alzheimer disease: However, in this study the beneficial association with Alzheimer’s disease was due to a significant association with a variant in the GC gene coding variations in the vitamin D binding protein, while in line with our study, no associations were seen for DHCR7, or CYP2R1. As we have described earlier, while associated with 25(OH)D concentrations, GC is not suitable for the use as its’ proxy marker in Mendelian randomisation analyses, given likely influences on bioavailability of 25(OH)D29.