GAMETOPATHIES

From Big Medical Encyclopedia

GAMETOPATHIES (gametes + grech, pathos suffering, a disease) — group of inborn diseases which developing is caused by changes of genetic material in the course of maturing of sex cells (pathology of a gametogenesis) or during fertilization and on the first reduction stages of an oospore (zygote). Can be such changes or disturbances of quantity of chromosomes (a polyploidy or an aneuploidy) or structures of chromosomes (structural aberation chromosomes).

The term «Gametopathies» is inexact as and at the hereditary diseases caused by mutant genes (see. Mutation ), certain changes of molecular structure of DNA of chromosomes of gametes take place (point mutations). Besides, similar disturbances of embryonic development can arise because of patol, the changes which are not affecting the genetic device of sex cells (see. Genome ).

Increase in number of genomes (a triploidy, a tetraploidiya etc.) is observed as a result of fertilization of an ovum by two and more spermiya or if one of sex cells which is taking part in fertilization keeps not reduced (diploid) quantity of chromosomes. Disturbances of discrepancy of homologous chromosomes during maturing of gametes (see. Meiosis ) or during division of a zygote (see. Mitosis ) lead to emergence of aneuploid cells, i.e. there is a lot of cells or shortage of one chromosome. At meiotic not discrepancy both homologous chromosomes get to one sex cell, and the second sex cell loses this chromosome. If the sex cell with an excess chromosome then there is a germ with a trisomy takes part in fertilization, and with participation in fertilization of a cell with shortage of a chromosome — a germ with a monosomy. Sometimes chromosomal anomalies bear both sex cells which are taking part in fertilization. In this case the germ with difficult aberation chromosomes develops. At not discrepancy of homologous chromosomes during division of a zygote one of blastomeres receives an excess chromosome whereas another loses this chromosome. If at the same time the germ does not perish and development of both blastomeres continues, then there is genetic mosaicism (see), i.e. the germ consists of cells both with a trisomy, and with a monosomy. Can be caused also by such changes of a separate chromosome as loss of the site of a chromosome (deletion), transfer of the site of one chromosome on another (translocations), change of an arrangement of certain sites as a part of a chromosome (inversion), etc.

Chromosomal anomalies in sex cells have various effects. In some cases sex cells with aberation chromosomes are not capable to take part in fertilization, as serves as the reason of some forms of infertility. In other cases sex cells with anomalies of chromosomes take part in fertilization and, thus, are transferred to cells of a germ. Extent of disturbance of development of germs in these cases depends on weight of aberation chromosomes. The most initial reduction stages, up to formation of a blastocyste, apparently, can be carried out at any aberation chromosomes. The majority of germs with aberation chromosomes perishes during pre-natal development, and the aberation chromosomes are expressed stronger, the germ perishes earlier. Considerable number of spontaneous abortions (see. Misbirth ) it is caused by aberation chromosomes. At earlier stages germs with aberrations of the large chromosomes bearing a lot of genetic information perish, and the monosomy affects more adversely an embryogenesis, than a trisomy. The aberration of some chromosomes leads to characteristic disturbances organogenesis (see), and ugly fruits perish at the end of the pre-natal period or soon after the birth. Achievements of cytogenetics allowed to establish interrelation between nek-ry disturbances of pre-natal development (see. Fetopathies , Embryopathies ) and certain types of aberation chromosomes (see. Chromosomal diseases ). The reasons causing quantitative and structural aberation chromosomes in sex cells are found out, however, not completely. Frequency of not discrepancy of chromosomes in sex cells increases only at women with age that, perhaps, is connected with disturbance of hormonal balance, pathology of an ovulatory cycle and overripening of sex cells in follicles or out of them. It is possible that not discrepancy of chromosomes in sex cells is caused also by action on an organism of the damaging agents of external environment — ionizing radiation, some chemical and infectious agents (see. Mutagenesis , Radiation, genetic effect ).

See also Antenatal pathology , Hereditary diseases , Malformations .


Bibliography: Fundamentals of cytogenetics of the person, under the editorship of A. A. Prokofieva-Belgov-skoy, M., 1969, bibliogr.; Efroimson V. P. Introduction to medical genetics, M., 1968; S and x yo n L. a. R and r about-la J. Congenital defects, N. Y., 1969.

A. P. Dyban.

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