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.