Chapter 64 - Pseudo-vitamin D Deficiency

Abstract

Pseudo-vitamin D deficiency rickets (PDDR) is a rare autosomal recessive disorder caused by mutations in the gene encoding 1α-OHase (CYP27B1), leading to an inability to synthesize 1,25(OH)2D. This disease was the first described inborn error of vitamin D metabolism and has contributed in a major way to the understanding of vitamin D biology. Patients with PDDR are healthy at birth and the first symptoms usually appear within the first year of life. The distribution of presenting signs and symptoms seems to differ somewhat between PDDR and vitamin D deficiency rickets. Hypocalcemia is the cardinal feature in PDDR. Serum calcium concentration drops below 2 mmol/l (8 mg/ dl). This, particularly if the decrease is rapid, may give rise to tetany and convulsions, which may occur prior to any radiological evidence of rickets. The treatment of choice for PDDR patients is replacement therapy with small daily doses of calcitriol. Started in infancy, this treatment results in short- and long-term correction of all clinical, biochemical, and radiological abnormalities related to PDDR, without serious adverse events. Because of the easiness and efficacy of the replacement therapy, it is unlikely that any form of gene-based therapy will be considered anytime soon.