Introduction
Vitamin D is a hormone commonly produced by UV exposure in the skin and is hydroxylated twice in the liver and renal tubules to produce the active form of vitamin D, 1,25-dihydroxyvitamin D (1,25 (OH)2 D). Vitamin D plays an important role in nutrient absorption, and vitamin D deficiency reduces calcium and phosphorus absorption by 10-15% and 60%, respectively. Vitamin D plays an immunomodulatory role against infections and cancer, and its levels are controlled by phosphorus, parathyroid hormone (PTH) and calcium. Impaired production of the active form of vitamin D is an inherited disorder that is the most common autosomal recessive form of rickets. Mutations in the CYP27B1 gene caused a form of rickets called VDDRIA by interfering with the active form of vitamin D (located on chromosome 12q13)(1). Symptoms usually appear in the first year of life and caused decreased serum calcitriol levels by inactivating synthesis of the enzyme 1 alpha-hydroxylase (2-4).
In contrast to the nutritional type of rickets, the vitamin D-dependent form is characterized by low serum calcitriol but not low levels of 25-hydroxyvitamin. The clinical laboratory profiles of these patients included high levels of PTH and alkaline phosphatase (ALP), but low serum calcium and phosphate level (2, 3). Typical signs in rickets patients who present with these symptoms, despite vitamin D supplementation, are increased fractures, rachitic rosary, growth failure, genu valgum, and hypotonia (2).
As a result, these patients respond well to products (calcitriol), substrates (1a-hydroxyvitamin D), vitamin D, and calcium supplementation and high cholecalciferol level is not helpful in these patients. Despite the efficacy of calcitriol in these patients, it is also associated with complications such as nephrocalcinosis, hypercalcemia, and hypercalciuria (5). We will introduce a 7-year-old girl, diagnosed as a case of VDDRIA and discuss her clinical and paraclinical findings.