Vitamin D-dependent rickets type II: report of a novel mutation in the vitamin D receptor gene

Hereditary vitamin D-resistant rickets type or vitamin D-dependent rickets type II is a genetically determined and rare autosomal recessive disorder, most often caused by mutations in the vitamin D receptor gene. It usually presents with rachitic changes not responsive to vitamin D treatment and the circulating levels of 1,25 (OH)2 vitamin D-3 are elevated, differentiating it from vitamin D-dependent rickets type I. Alopecia capitis or alopecia totalis is seen in some families with vitamin D-dependent rickets type II. This is usually associated with a more severe phenotype. In this report, we present the clinical findings on a family which exhibited the typical clinical features of hereditary vitamin D-resistant rickets in two siblings. In addition, molecular analysis of the vitamin D receptor gene was performed by sequencing all coding exons. The cardinal findings in the index patient were alopecia totalis, renal tubular acidosis, mild generalized aminoaciduria, refractory rickets, high alkaline phosphatase, and hyperparathyroidism. Other routine biochemical tests were within normal limits, but 1+ glycine was detected in his urine. Skin biopsy results were compatible with alopecia areata. A previous child with similar phenotype was reported to be deceased at the age of 32 months. Mutation analysis of the vitamin D receptor gene by direct sequencing analysis of all coding exons showed a homozygous c.122GA(p.Cys41Tyr) variant in exon 2 with several arguments pointing to a pathogenic effect. We should be aware of this very rare disease whenever we see a patient with refractory rickets and alopecia.