The kariotype variability in children with Down syndrome from the Odesa region

Abstract

The aim of the work is to analyze the frequency of cytogenetic variants of Down syndrome among patients in Odesa and the region, as well as to identify combined karyotype anomalies. Materials and methods. Studies were conducted between 2013–2018 years in Odesa Specialized Medical Genetic Center. The experimental group was formed of patients with cytogenetically confirmed Down syndrome. Chromosomes were painted according to GTG method and identified according to ISCN 2013. Results. Among patients with Down syndrome, in 93.9 % of cases complete trisomy 21 was observed, the translocation form was in 3.7 %, and the mosaic form was in 2.4 %. Similar results were revealed in the analysis of populations belonging to different ethnic and racial groups. Complete trisomy 21 was accompanied by chromosome rearrangements of other chromosomes or additional modifications of chromosome 21. Changes in the heterochromatin in chromosome 9 were more frequently observed. In total, 5.5 % of examined karyotypes were found with additional heterochromatin in both arms of chromosome 1 and in the long arm of chromosome 21. An increase in the size of satellites in chromosomes 14, 15 and more often 21, as well as the appearance of additional satellites in chromosome 2 represented 3.6 % of the total examined karyotypes. A deletion on chromosome 6 involved in translocation with chromosome 13 also was found. Translocation forms included Robertsonian translocations involving chromosomes 21 and 21, 14 and 21, as well as translocations involving chromosomes 21 and 21, 21 and 22. Patients with a mosaic form of the disease had two cell lines: with a normal karyotype 3 (15–67 % of the studied cells) and with complete trisomy 21 without additional chromosomal abnormalities (33–85 % of the studied cells). Conclusions. Among patients with cytogenetically confirmed diagnosis of Down syndrome, the ratio of the main variants was similar to many populations studied. At the same time, additional changes in the karyotype were identified which can either be a variant of the norm or aggravate the course of the disease. This requires further studies of the disease course in such patients.