Calcidiol is transported to the kidney for a second hydroxylation through the 1-α-hydroxylase enzyme (CYP27B1) in the proximal convoluted tubule, generating 1,25(OH)2D3 (calcitriol), the active form of vitamin D. In clinical practice, measurement of circulating 25OHD is preferred to diagnose vitamin D status since calcitriol has a short half-life of less than 6 h, its hydroxylation in the kidney is regulated by several factors, and its levels can be normal or even increased in patients with vitamin D deficiency due to the stimulus of parathormone (PTH) [1,12]. This evidence concerns the gene PTH and vitamin D deficiency.