Hypocalcemic vitamin D-resistant rickets (HVDRR) is a hereditary disorder of vitamin D action characterized by hypocalcemia, severe rickets and in many cases alopecia.
The prevalence is unknown.
Progressive rickets manifests during the first years of life with poor growth and skeletal deformities. Total body alopecia is present in severe forms of the disease (2/3 of cases). In some cases, skin lesions or epidermal cysts can be observed along with alopecia. The disease presents a broad clinical picture that largely depends on the genotype.
The disease is due to mutations in the vitamin D receptor gene (VDR; 12q13-14) that decrease the receptor's action thereby preventing calcitriol's action. This leads to an impaired intestinal absorption of calcium due to functional vitamin D deficiency. Transmission is autosomal recessive.
Diagnosis is based on clinical, biochemical and radiological findings. Biochemical features are severe hypocalcemia, hypophosphatemia, secondary hyperparathyroidism, normal serum levels of calcidiol (25-hydroxyvitamin D), elevated serum levels of calcitriol (1,25-dihydroxyvitamin D3, the active form of vitamin D), high serum levels of alkaline phosphatase and aminoaciduria. Radiological findings include typical rickets and osteomalacia (skeletal deformities affecting the growth plates and metaphyseal bone, trabeculation of long bones, vertebral anomalies). Osteitis fibrosa cystica is commonly observed.
Differential diagnosis of HVDRR includes other forms of rickets (hereditary and nutritional) and atrichia with papular lesions (APL) and hypocalcemic vitamin D-dependent rickets (see these terms).
Treatment aims at improving growth, correcting hypocalcemia and hyperparathyroidism, and at enhancing mineralization of bones. It consists of daily administration of high doses of calcitriol and calcium; intravenous administration may be needed. Response to treatment largely depends on the severity of the disease. HVDRR patients with alopecia generally do not respond to oral treatment and need intravenous calcium infusions. Regular monitoring of biochemical parameters is required.
Correction of rachitic deformities depends on the severity of the disease.
Last update: January 2012