Presence of a deletion mutation (c.716delA) in the ligand binding domain of the vitamin D receptor in an Indian patient with vitamin D-dependent rickets type II.

Vitamin D-dependent rickets type II (VDDR-type II) is a rare disorder caused by mutations in the vitamin D receptor (VDR) gene. Here, we describe a patient with VDDR-type II with severe alopecia and rickets. She had hypocalcemia, hypophosphatemia, secondary hyperparathyroidism, and elevated serum alkaline phosphatase and 1,25-dihydroxyvitamin D(3). Sequence analysis of the lymphocyte VDR cDNA revealed deletion mutation c.716delA. Sequence analysis of her genomic DNA fragment amplified from exon 6 of the VDR gene incorporating this mutation confirmed the presence of the mutation in homozygous form. This frameshift mutation in the ligand binding domain (LBD) resulted in premature termination (p.Lys240Argfs) of the VDR protein. The mutant protein contained 246 amino acids, with 239 normal amino acids at the N terminus, followed by seven changed amino acids resulting in complete loss of its LBD. The mutant VDR protein showed evidence of 50% reduced binding with VDR response elements on electrophoretic mobility assay in comparison to the wild-type VDR protein. She was treated with high-dose calcium infusion and oral phosphate. After 18 months of treatment, she gained 6 cm of height, serum calcium and phosphorus improved, alkaline phosphatase levels decreased, and intact PTH normalized. Radiologically, there were signs of healing of rickets. Her parents and one of her siblings had the same c.716delA mutation in heterozygous form. Despite the complete absence of LBD, the rickets showed signs of healing with intravenous calcium.

Pattern of 25-hydroxy vitamin D response at short (2 month) and long (1 year) interval after 8 weeks of oral supplementation with cholecalciferol in Asian Indians with chronic hypovitaminosis D.

Hypovitaminosis D is common in Asian Indians. Physicians often prescribe 1500 mug (60 000 IU) cholecalciferol per week for 8 weeks for vitamin D deficiency in India. Its efficacy to increase serum 25-hydroxy vitamin D (25(OH)D) over short (2 months) and long (1 year) term is not known. We supplemented a group of twenty-eight apparently healthy Asian Indians detected to have low serum 25(OH)D (mean 13.5 (sd 3.0) nmol/l) on screening during January-March 2005. Serum parathyroid hormone (PTH) level was supranormal in 30 % of them. Oral supplementation included 1500 mug cholecalciferol per week and 1g elemental Ca daily for 8 weeks. Serum 25(OH)D, total Ca, inorganic P and intact (i) PTH were reassessed in twenty-three subjects (twelve females and eleven males) who had follow up at both 8 weeks and 1 year. At 8 weeks the mean 25(OH)D levels increased to 82.4 (sd 20.7) nmol/l and serum PTH normalized in all. Twenty-two of the twenty-three subjects had 25(OH)D levels>49.9 nmol/l. At 1 year, though the mean 25(OH)D level of 24.7 (sd 10.9) nmol/l was significantly higher than the baseline, all subjects were 25(OH)D deficient. Five subjects with supranormal iPTH at baseline showed recurrence of biochemical hyperparathyroidism. Thus, with 8 weeks of cholecalciferol supplementation in Asian Indians with chronic hypovitaminosis D, mean serum 25(OH)D levels would be normalized and serum PTH value would be reduced to half. However, such quick supplementation would not maintain their 25(OH)D levels in the sufficient range for 1 year. For sustained improvement in 25(OH)D levels vitamin D supplementation has to be ongoing after the initial cholecalciferol loading.