Because the concentration of mitochondrial 1alpha-OHase in the kidney and 1,25(OH)2D3 in the serum and kidney were decreased after 3 months of treatment with Cd at 5 mg/kg of diet, hypocalcaemia caused by this toxic element (at enhanced sRANKL concentration in the bone tissue and serum indicating enhanced bone resorption [17]) may be explained by insufficient gastrointestinal absorption of Ca. This evidence concerns the gene CYP27B1 and Hypocalcemia.