A Case of Vitamin D-Dependent Rickets Type 1A with a Novel Mutation in the Uzbek Population

Abstract

Vitamin D-dependent rickets type 1A (VDDR-1A) (Online Mendelian Inheritance in Man #264700) is a rare, autosomal recessively inherited disorder due to inactivating mutations in CYP27B1. It is characterized by early onset of rickets with hypocalcemia. We aimed to describe the clinical and laboratory findings in a VDDR-1A case and to report a novel homozygote truncating mutation NM_000785.3 c.403C>T (p.Q135*) in CYP27B1 which to our knowledge is the first described mutation in the Uzbek population. The patient was admitted with tetany at the age of 12 months. He was a healthy Uzbek boy until 9 months of age when he had a seizure due to hypocalcemia. Vitamin D treatment was given orally in Turkmenistan (no data available for dose and duration). The patient was the product of a consanguineous marriage. His brother had died with hypocalcemia and pneumonia. At physical examination, anthropometric measurements were within normal limits; he had caput quadratum, enlarged wrists, and carpopedal spasm. Blood calcium, phosphorus, alkaline phosphatase, and parathormone (PTH) levels were 5.9 mg/dL, 3.5 mg/dL, 987 IU/L, and 182.8 pg/mL (12-72), respectively. Radiological findings included cupping and fraying of the radial and ulnar metaphyses. Renal ultrasound revealed nephrocalcinosis (grade 1). Despite high serum PTH and 25-hydroxyvitamin D3 levels, 1,25-dihydroxyvitamin D3 level was low, suggesting a diagnosis of VDDR-1A. The patient was treated with calcium carbonate and calcitriol. DNA sequencing revealed a novel homozygous mutation of NM_000785.3 c.403C>T (p.Q135*) in CYP27B1. VDDR-1A is a rare disorder which needs to be considered even in countries where nutritional vitamin D deficiency is still common.