Vitamin D Dependent Rickets – Type II (VDDR-II)
VDDR-II is a very rare form of rickets.
It is an autosomal recessive disorder.
It is associated with end-organ resistance to 1,25(OH) 2 D.
VDDR-II is associated with end-organ resistance to 1,25(OH) 2 D, usually caused by mutations in the gene encoding the vitamin D receptor.
The defect in the receptor interferes with the function of the hormone-receptor complex, thereby preventing 1,25(OH) 2 D action.
The clinical spectrum of VDDR II varies widely with the type of mutation.
Affected children usually appear normal at birth, but develop rickets within the first 2 years of life.
Alopecia is seen resulting from the lack of vitamin D receptor activity within keratinocytes develops in approximately two-thirds of cases and is a marker of disease severity.
Serum calcium – Low
Serum phosphate – Low
Serum alkaline phosphatase – Increased
Parathyroid hormone assay – increased
25(OH) vitamin D – Normal or elevated
1,25(OH)2 vitamin D – Severely elevated
The treatment of VDDR II consists of a therapeutic trial of 1,25(OH) 2 D (calcitriol) and calcium.
The severity of the receptor defect varies among patients.
Therapy is started at daily doses of 2 μg of 1,25 (OH) 2 D and 1 g of elemental calcium. However, in some cases administration of very high doses of 1,25(OH) 2 D (up to 60 μg/day) and calcium (up to 3 g per day) may be necessary.
Intravenous calcium infusion into the central vein may be needed for resistant patients and must be continued for many months.
Oral calcium therapy may be sufficient once radiographic healing has occurred.