This subnormal calcitriol value may be surprising at first glance, as no difference is detected for PTH values between the two groups, and thus is likely related to high serum phosphate [4,5,6,7,8] and high FGF23 concentrations in SCD patients [8,50,51], which would exert an inhibitory effect on calcitriol synthesis by the proximal tubule [49]. The gene discussed is PTH; the disease is Schnyder corneal dystrophy.