Growth indices and vitamin D content in children with idiopathic short stature depending on the variants of the Taql polymorphism genotype of the VDR gene

Abstract

Background. The vitamin D receptor (VDR) gene is a key regulator of biological processes, including tissue and cell growth and differentiation, bone metabolism, and modulation of immune responses. Several studies have shown that 1,25(OH)2D increases circulating insulin-like growth factor-1 (IGF-1) levels in vivo and in bone cell cultures. It also increases the expression of IGF-1 receptors in growth plate chondrocytes and several IGF-binding proteins in osteoblasts and bone marrow stromal cell cultures. A vitamin D receptor gene polymorphism is associated with adult height and may affect the growth indicators in children with idiopathic short stature. The purpose was to study the growth indicators and vitamin D levels in children with idiopathic short stature depending on the variants of the Taql polymorphism genotype of the VDR gene. Materials and methods. Determination of the Taql polymorphism of the VDR gene (rs731236) was performed using polymerase chain reaction followed by an analysis of the length of the restriction fragments when detected by agarose gel electrophoresis in 35 children with idiopathic short stature. Results. Most children (68.57 %) were heterozygotes, 17.14 % were homozygotes for T/T alleles, and 14.29 % were homozygotes for C/C alleles. The highest growth retardation has been observed in homozygous T/T carriers. Children carrying homozygotes for C/C alleles had the least growth retardation. Growth hormone levels after clonidine stimulation test and IGF-1 levels in blood were within normal limits in all patients. Vitamin D deficiency was found in T/T homozygotes and vitamin D insufficiency in C/T heterozygotes and C/C homozygotes. Conclusions. Among children with idiopathic short stature, the prevalence of the T/C genotype was 68.57 %. The greatest growth retardation occurred in patients with homozygous T/T alleles (SDS = –2.61 ± 0.31). A decrease in serum vitamin D levels was detected in all children. Vitamin D deficiency (43.83 ± 6.47 nmol/l) was found in children homozygous for the T/T allele, and vitamin D insufficiency — in T/C heterozygotes (58.97 ± 11.78 nmol/l) and C/C homozygotes (56.93 ± 19.54 nmol/l).