VDDR-I is an autosomal recessive disorder.

It is characterized by the defective conversion of 25OHD-1,25(OH) 2 D.

It is also called pseudovitamin D deficiency rickets

VDDR-I is caused due to 1-alpha-hydroxylase deficiency.

Patients with VDDR-I have inactivating mutations in the CYP27B1 gene which encodes the enzyme 1-alpha hydroxylase responsible for the conversion of 25OHD to 1,25 (OH) 2 D.

VDDR-I is characterized by early onset of rickets (within the 1 st year of life) and severe hypocalcemia (sometimes with tetany), with accompanying moderate hypophosphatemia.

Enamel hypoplasia may occur.

Serum calcium – Low

Serum phosphate – Low

Serum alkaline phosphatase – Increased

Parathyroid hormone assay – increased

25(OH) vitamin D – Normal

1,25(OH)₂ vitamin D –  Severely decreased

The treatment for VDDR-I is 1,25 (OH) 2 D (calcitriol).

The initial dose for rickets is 1 μg/day till bone healing occurs. Later the dose is reduced to 0.25 and 1 μg/day.

Adequate intake of dietary calcium (30-75 mg/kg/day of elemental calcium) should be maintained.

Possible side effects of 1,25(OH) 2 D therapy include hypercalcemia, hypercalciuria, nephrocalcinosis, and intraocular calcifications. Therefore, it is important to check the urinary calcium/creatinine ratio and kidney function (e.g. serum creatinine) at each visit.

Renal ultrasound and ophthalmologic consultation (slit-lamp examination) should be performed once per year.