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Down syndrome is a severe pathology characterized by multiple malformations. The severity of defects can vary widely depending on the form of the syndrome and the number of mutant cells. Congenital defects in Down syndrome include: tetrad of Fallot (stenosis of the output part of the right ventricle, ventricular septal defect, aortic dextraposition and hypertrophy of the right ventricle), defects in the development of the neural tube, leading to mental retardation, and, in many cases, mental retardation, defects of the organs of vision and hearing, thyroid dysfunction and others. All these defects develop for the reason that the genome of a fetus with Down syndrome contains a trisomy of 21 pairs of chromosomes – instead of two, there are three chromosomes in 21 pairs. Thus, the genome in Down syndrome has the form 47XX or 47XY. In addition, a translocation form of the syndrome is possible, in which the long arm of chromosome 21 is attached to another (most often the 14th) chromosome. Then the genotype of the fetus can be written as 45 XX(14; 21) or 45 XY(14; 21). In this case, there are features of the course and diagnosis of the syndrome. If we talk about epidemiology, before the introduction of prenatal screening into obstetric practice, the frequency of birth of children with the syndrome was 1 case per 700 births. Now diagnostic methods have stepped far forward and many parents prefer to terminate a pregnancy in a situation when it turns out that the fetus has a genetic deviation. This practice has made it possible to reduce the birth rate of children with the syndrome to 1 case per 1100 births (according to WHO). In this article, modern diagnostic methods, their positive and negative sides, accuracy and specificity will be considered, as well as a methodology for their complex use is proposed.
Keywords:screening, pregnancy, research, prenatal, down syndrome.
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