A POSSIBLE GENETIC-DEFECT IN 25-HYDROXYLATION AS A CAUSE OF RICKETS

We examined two siblings who had severe rickets at ages 2 and 7 years, respectively, despite a history of adequate vitamin D intake. The pat ients' sera had calcium concentrations at the lower limits of normal, low phosphate concentrations, elevated alkaline phosphatase activity, and low levels of 25-hydroxyvitamin D. Treatment with high doses of vi tamin D-2 resulted in resolution of the biochemical abnormalities and radiographic deformities; pharmacologic doses of vitamin D-2 were requ ired to maintain normal concentrations of 25-hydroxyvitamin D in the s erum even though vitamin D absorption was normal. These children may h ave a genetic defect of the 25-hydroxylation step in vitamin D activat ion.