Figure 1. Genetic variations in the enhancer-like regions downstream of the Cyp24a1 gene regulate its basal expression in different strains of inbred mice. Deletions and substitutions in the putative Cyp24a1 regulatory sequences in susceptible C3H, BALB/c and 129 mice lead to reduced basal expression of the gene, compared to resistant C57BL/6 mice, and render susceptible strains to high levels of vitamin D in the serum and aging-related detrimental phenotypes with decreased Klotho expression.