Meta-Biol

• Pathways

The second step in vitamin D3 activation requires hydroxylation of 25-hydroxyvitamin D3 (calcidiol) to 1alpha-25-dihydroxyvitamin D3 (calcitriol). This conversion is mediated by 25-hydroxyvitamin D-1alpha hydroxylase (CYP27B1) (Zehnder et al. 2002, Fritsche et al. 2003). Defects in CYP27B1 can cause rickets, vitamin D-dependent 1A (VDDR1A; MIM:264700), a disorder caused by deficiency of the active form of vitamin D (CTL) resulting in defective bone mineralization and clinical features of rickets (Kim 2011). Mutations causing complete loss of function of CYP27B1 include R107H, G125E, R335P, P382S, R389G, R389H and D320Tfs*32 (Kitanaka et al. 1998, Wang et al. 2002, Wang et al. 1998).