Chromosomal diseases are caused by chromosomal and genomic mutations, i.e. associated with a change in the structure or number of chromosomes. In most cases, the cause of genomic mutations is a violation of the divergence of chromosomes in meiosis (with the formation of gametes).
– Shereshevsky-Turner syndrome develops in girls with the chromosome set 44A + X0 (there is no second X chromosome). Frequency of occurrence 1: 3000 newborn girls. Patients are characterized by low growth (140 cm on average), a short neck with deep skin folds from the back of the head to the shoulders, shortening of the 4th and 5th fingers, lack or weak development of secondary sexual characteristics, infertility. In 50% of cases, mental retardation or a tendency to psychosis is observed.
– The syndrome of polysomy on the X chromosome in women may be due to trisomy (44A + XXXX), tetrasomy (44A + XXXXX) or pentasomy (44A + XXXXXX). Trisomy occurs with a frequency of 1: 1000 babies. Manifestations are quite diverse: there is a slight decrease in intelligence, it is possible the development of psychosis and schizophrenia, impaired ovarian function. With tetrasomy and pentasomy, the likelihood of mental retardation increases, and the underdevelopment of primary and secondary sexual characteristics is noted.
– Kleinfelter’s syndrome is observed with a frequency of 1: 500 newborn boys. Patients have an extra X chromosome (44A + XXY). The disease manifests itself during puberty and is expressed in the underdevelopment of the genitals and secondary sexual characteristics. Men with this syndrome are characterized by high growth, a female body type (narrow shoulders, wide pelvis), enlarged mammary glands, and weak facial hair growth. Patients have impaired spermatogenesis and in most cases they are infertile. Lag of intellectual development is observed in 5% of cases.
– Down syndrome is caused by trisomy on the 21st chromosome. The average frequency of the disease is 1: 700 newborns. Patients are characterized by short stature, a round flattened face, a mongoloid eye section with an epicanthus (an overhanging fold over the upper eyelid), small deformed ears, a protruding jaw, a small nose with a wide flat nose bridge, and impaired mental development. The disease is accompanied by a decrease in immunity, a violation of the endocrine glands. About half of patients have malformations of the cardiovascular system.