Genetics, Medical

a branch of human genetics that studies hereditary diseases and methods of preventing, diagnosing, and treating them. The existence of diseases transmitted by heredity (for example, hemophilia), as well as the fact that marriages between relatives increase the frequency of hereditary diseases in the offspring, has been known for a long time. In the early 20th century the main subject of investigation was the correlation between heredity and the environment in the origin of both normal and pathological traits in man.

The study of medical genetics originated in Russia only with the establishment of Soviet power. Considerable progress was made in the field in the 1930’s. The Institute of Medical Genetics, which was directed by S. G. Levit, successfully studied the inheritance of such diseases as diabetes mellitus, ulcers, and hypertension. S. N. Davidenkov and his school made a comprehensive study of hereditary diseases of the nervous system.

In studying hereditary diseases medical genetics uses all the methods of human genetics, including genealogy, which involves preparing a genealogy to show the relationship between the healthy and sick members of the family of a subject—that is, the patient for whom the genealogy is compiled. Medical genetics also studies twins and uses cytological, biochemical, and immunological methods of research. In the 1960’s cytogenetic research methods for studying chromosomes and sex chromatin and biochemical tests acquired considerable importance. Hereditary diseases were found to depend on changes in the chromosomes of germ cells—that is, changes in the structure of genes, chromosomal aberrations (deletions, translocations, duplications), or quantitative changes in the chromosome set (addition or loss of one or more chromosomes). For example, a disorder in the number or structure of the sex chromosomes or autosomes gives rise to such hereditary diseases as Turner-Shereshevskii syndrome, mongolism, Klinefelter’s and cat’s cry syndromes, trisomy 18 (Edwards), and trisomy D (Patau). Visible defects in the chromosome set have not been discovered in other hereditary diseases, which are apparently caused by gene mutations or an unfavorable combination of different genes.

The manifestation of certain hereditary diseases depends on environmental factors that promote the development of a hereditary predisposition or its complete suppression. The task of medical genetics is to find suitable environmental conditions (including medication, and diet). Advances in medical genetics made it possible to prevent and treat a number of hereditary diseases. One effective method of prevention is medicogenetic consultation, with a prediction of the risk of the appearance of a given hereditary disease in one of the offspring of individuals suffering from that disease or having a relative with the disease. Research in biochemical genetics revealed primary (molecular) defects in many hereditarily determined metabolic anomalies. This led to the development of methods of rapid diagnosis, making possible the quick and early detection of sick persons and treatment of many previously incurable diseases. For example, the use of a special diet can prevent phenylketonuria (phenylpyruvic oligophrenia) and some other hereditary diseases. In other cases treatment involves injecting substances not produced in the body as a result of a genetic defect. Many genetic defects are corrected by timely surgery or training.

In many countries there are clinics and research institutes concerned with the hereditary pathology of man—for example, the Institute of Medical Genetics of the Academy of Medical Sciences of the USSR. About 3,000 articles are published on medical genetics every year in Acta geneticae medicae et gemellologiae (Rome, since 1952), American Journal of Human Genetics (Baltimore, since 1949), Annals of Human Genetics (London, since 1954), Journal de génétique humaine (Geneva, since 1952), Journal of Medical Genetics (London, since 1964), and Excerpta medica, Section 22: Human Genetics (Amsterdam, since 1962). In the USSR articles on medical genetics are published in many medical and biological journals, such as Genetika (Genetics), Tsitologiia (Cytology), and Tsitologiia i genetika (Cytology and Genetics).