Cytogenetic techniques in current biomedical research. PART III: numerical alterations of human karyotype

Numerical abnormalities of karyotype are the result of genome mutations. Unlike gene and chromosomal abnormalities, genome mutations do not disrupt the structure of DNA or chromosomes. The cause of numerical changes in the karyotype is a violation of the mechanism of chromosome segregation during meiosis or mitosis. Like other mutations, genome mutations are a natural mechanism for increasing of genetic diversity in offspring. At the same time, humans usually have negative effects of any numerical deviations from the norm, for this reason, cytogenetic examination of aneuploidies is an important diagnostic tool in medical genetics.
A change in the number of sex chromosomes is usually not lethal. The spectrum of detected deviations in the carrier is from inconstant impairment of reproduction but a normal phenotype to malformations of some internal organs, infertility and severe intellectual disabilities. Aneuploidies of autosomes are always a threat to life and health. Only autosomal trisomies on chromosomes 13, 18, 21 and 22 are compatible with live birth, there are solitary reports of the birth of children with polyploidies. At the same time, the prognosis of life is relatively favorable only in the case of trisomy 21, leading to the formation of Down syndrome. Other aneuploidies usually lead to spontaneous termination of pregnancy in the early stages and are discovered in samples of abortion material.
In this regard, cytogenetic analysis of chromosomal aneuploidies is used to establish the genetic cause of anomalies and malformations in the postnatal period, delays in speech and psychomotor development, reproduction disorders in adults. Of particular importance is the cytogenetic analysis of the karyotype of embryos in the prenatal period. The proposed lecture analyzes the mechanism of formation of genomic mutations and their diversity. The possible medical consequences of the presence of various types of aneuploidies are considered. To the reader attention is offered syndromes associated with a change in the number of chromosomes in the karyotype. The description is illustrated by real images of patient karyotypes.
The lecture is aimed primarily at students of medical and biological specialties, young specialists who plan to use cytogenetic research methods in their practical activities, and doctors who are faced with the need to analyze and interpret the results of cytogenetic analysis. To assimilate the material under discussion, it is recommended to familiarize yourself with the previous lecture of the cycle.

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