Clinical and Genetic Characterization of Tunisian Children with Hereditary 1,25-Dihydroxyvitamin D-Resistant Rickets

Background: Hereditary vitamin D-resistant rickets (HVDRR) is an autosomal recessive disorder characterized by the early onset of rickets and is caused by mutations in the vitamin D receptor (VDR) gene. Some HVDRR patients also have alopecia.

Patients And Methods: We retrospectively studied the clinical features, laboratory findings, genetic defects, as well as responses to treatment in a series of children with HVDRR.

Results: Eight patients from 7 families met the inclusion criteria. Alopecia was noted in 7 patients. Two different homozygous mutations in the VDR gene were identified in 6 patients: the p.K45E mutation located in the DNA-binding domain (5 patients with alopecia) and a novel p.T415R mutation located in the ligand-binding domain. A p.E143del CYP24A1 mutation, in the gene encoding the 25-hydroxyvitamin D3-24-hydroxylase, was identified in 2 brothers carrying the VDR gene mutation p.K45E. Six patients were treated with intermittent intravenous calcium treatment via the peripheral route with a clear improvement in 5 cases.

Conclusion: To the best of our knowledge, this is the first major series reporting on HVDRR in Tunisia. The same mutation (p.K45E) was found in 5 apparently unrelated affected individuals. We have also extended the mutation spectrum by studying 1 novel VDR mutation.