VITAMIN D DEPENDENCY: AN INHERITED POSTNATAL SYNDROME WITH SECONDARY HYPERPARATHYROIDISM

Abstract

Three French-Canadian children in a large inbred pedigree each developed hypocalcemic, hypophosphatemic rickets in the latter half of their first year of life; there were also manifestations of generalized renal tubular dysfunction. These abnormalities, which mimic advanced Vitamin D deficiency, disappeared only when Vitamin D2 or D3 was given at about 100 times the recommended daily allowance; this indicated the diagnosis of Vitamin D dependency. Enamel hypoplasia was a prominent clinical finding; only those teeth which calcify postnatally were affected, indicating that the condition found does not affect Vitamin D-dependent nutrition in utero. The level of parathyroid hormone was elevated in serum before treatment; it fell to normal either after treatment with Vitamin D, or during intravenous infusion with a calcium solution sufficient to produce hypercalcemia. Vitamin D dependency appeared to be inherited as an autosomal recessive trait in this pedigree, but we could observe no phenotypic signs in presumably obligate heterozygotes. One of the three cases in the pedigree arose from outbreeding, suggesting that the mutant allele is probably not particularly rare in the population under our surveillance.