Background. Familial hypercholesterolemia (FHC) is one of the most common monogenic diseases transmitted from parents to children, leading to disability and mortality in working age. Elevated total cholesterol and low-density lipoprotein cholesterol levels are detected in patients with this diagnosis already in childhood. Vascular endothelium is an active endocrine organ, the largest in the body, diffusely scattered along with vessels throughout all tissues. It has been proven that most of the risk factors for atherosclerosis realize pathogenic effects through endothelial dysfunction. In this regard, it is important to study the function of the endothelium as a model of atherosclerosis in patients with FH.
Objective. Evaluation of the endothelial function in children with heterozygous form of FH depending on their age.
Methods. For the period from 2017 to 2019, the medical records of 61 patients over 18 years of age with a diagnosis of heterozygous form of FH were analyzed on the basis of the Kazan City Clinical Hospital № 7. The next step was a cascade screening – a step-by- step identification of patients with FH among members of the proband’s family. The main study group consisted of 44 children who were diagnosed with a heterozygous form of FH according to the Simon Broome Registry criteria. The comparison group consisted of 43 relatively healthy children aged 5 to 17 years 11 months and 29 days inclusive, with no changes in the lipid profile. Children of the comparison and main groups were divided into 3 age subgroups: 5–7 years old, 8–12 years old, 13–17 years old.
Results. The maximum increase in the parameters studied was found in the group of older patients with FH aged 13–17 years compared with children in the younger age group 5–7 years, which demonstrates the prognostic value of vasoconstriction at the stages of the disease formation. As the age of patients and, accordingly, the duration of the disease increased, the production of nitric oxide increased significantly.
Conclusion. FH in children was accompanied by impaired endothelial function in the form of an increase in the endothelin-1 and nitric oxide concentration. The results obtained allow to speak about a significant compensatory vasodilating ability of the endothelium, aimed at preventing the vasopressor activity of endothelin-1.

Keywords: familial hypercholesterolemia, nitric oxide, children, endothelin-1, endothelium