Densitometric features of bone tissue in children during the growth spurt considering the VDR gene polymorphisms and vitamin D level

Abstract

Background. The period of intensive growth in children is associated with active changes in the bone tissue architecture. A high level of bone mass accumulations was observed. Whether such processes are adequate depends on numerous factors, however, all of them are based on a genetic component. Gene expression affects all the processes in the body, including bone tissue. The BSML and Fokl polymorphisms of the VDR gene responsible for the activity of cell receptors for vitamin D is studied in association with bone pathology, autoimmune diseases, diseases of the central nervous, cardiovascular and other systems. Purpose – of the research is aimed at determining densitometric features of the structural and functional condition of bone tissue in children during the growth spurt, taking into account polymorphisms of BSML, FOKL gene VDR and vitamin D levels. Materials and Methods. The examination covered 205 healthy children aged 9–17, who were divided into groups depending on the presence or absence of growth spurt (GS) and its intensity. The examination presupposed analysis of the medical history, assessment of physical and sexual development, ultrasound (QUS) and X-ray (DXA) densitometry, determination of 25-(OH)-D levels, molecular diagnostics- definition of polymorphisms of BSML, FOKL gene VDR. Results. Ultrasound densitometry showed a decrease in bone mineral density (BMD) in 24 children of Group I (48.0%), Z-score: – 1.8 ± 0,56; 28 children in Group II (60.87%), Z-score: – 1.96 ± 0,27 and 43 children of Group III (39.45%), Z-score: – 1.68 ± 0,72. DXA was used for 32 children, 18 of them (56.25%) were diagnosed with a decreased BMD. Children of Group I with a reduced BMD had an average level of vitamin 25-(OH)-D at the value of 39.04 ± 11.84 nmol/l, while in children with a normal BMD it averaged – 42.43 ± 6.3 nmol/l. In children of group II BMD in which it was reduced, the average level of 25-(OH)-D was 45.68 ± 5.48 nmol/l, with normal BMD – 45.47 ± 4.69 nmol/l. Children of Group III with a reduced BMD had an average 25-(OH)-D level of 36.73 ± 8.94 nmol/l, those with a normal BMD showed the 25-(OH)-D level of 42.91 ± 9.1 nmol/l. A molecular study found that 48.76% of children did not have any mutations in the VDR gene BSML polymorphism, 41.32% of children showed a heterozygous mutation, and 9.92% of children revealed a homozygous mutation. 27.81% of children had no mutation of Fokl polymorphism in the VDR gene, 61.95% showed a heterozygous mutation and a homozygous mutation was detected in 10.24% of children. Conclusions. Decreased bone mineral density in children during growth spurt is due to insufficiency or deficiency of vitamin D and is determined genetically. However, the most significant factor in the BMD reduction is the retardation of bone mass accumulation processes against the background of an intensive linear growth of the skeleton.