TRPV6 and Marchiafava-Bignami disease: Mutations within these VDREs can render TRPV6 unresponsive to vitamin D. The decreased activity of 1α-hydroxylase leads to 1,25(OH)2D3 deficiency in the kidney of patients with CKD-MBD, which in turn leads to the decreased expression of TRPV5/TRPV6.