Gain-of-function mutations affecting CYP3A4 activity have previously been identified by whole-genome sequencing in patients with vitamin D-dependent rickets type 3 (Figure 2), showing an increased conversion of 25(OH)D3 and 1,25(OH)2D3 into their inactive forms [59], which exemplifies the enzyme’s potency in degrading vitamin D. The induction of hepatic CYP3A4 can be potently achieved by rifampicin [60]. Here, CYP3A4 is linked to Hypocalcemic vitamin D-resistant rickets.