Marked cartilaginous disorganization was seen in the growth plates of Cyp27b1-KO rats, Vdr (R270L) rats and Vdr-KO rats at 15 weeks of age, as evidenced by toluidine blue staining, indicating the histological features of rickets (Fig. 2a and Supplementary Fig. S8). Here, CYP27B1 is linked to rickets.