Chromosome defects (defects in the genetic make-up)

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The creation of new life is a highly complex process that can go wrong in various places: Chromosome defects are the possible consequences. Here you can find out how such defects in the genetic makeup arise and can be determined and what they may mean for the child!

What are chromosomes

Every human being has 46 chromosomes in every body cell, on which the entire genetic information is stored. Two of these, X and Y, are the sex chromosomes. These 46 chromosomes are made up of 23 pairs of chromosomes. The sexual hereditary disposition in girls is called 46XX because it has two X chromosomes. Boys each have an X and a Y chromosome, so the genetic makeup is abbreviated as 46XY.

Cell division and fertilization

The sex cells (egg cells, sperm cells) are the only cells in the body to have half the chromosome set (23 chromosomes): The egg cells contain chromosome set 23X in the nucleus, while the nucleus of the sperm cells has either chromosome set 23X or 23Y.

During fertilization - i.e. the fusion of egg and sperm cells - a cell with 46 chromosomes is created again, from which the child then develops. If the egg cell (23X) has united with a sperm cell of the 23X type, a girl (46XX) is created. When the egg cell fuses with a 23Y-type sperm cell, it becomes a boy (46XY).

A healthy child can develop if there are no abnormalities in the chromosomes in the mother and in the father and the fusion and subsequent cell divisions proceed normally.

Chromosome defects

There are a number of ways in which deviations from the normal chromosome order (so-called chromosome aberrations) can arise. Such errors can arise in every cell division, including the formation of egg and sperm cells, as well as in the fusion of egg and sperm cells during fertilization.

During cell division, for example, the chromosomes can be incorrectly distributed among the daughter cells. In the context of reproduction, this means that the number of chromosomes in the child is reduced or increased. The shape of individual chromosomes can also change, for example part of it can break off (structural chromosome defects).

Some genetic anomalies can arise from external influences, such as radiation or chemicals. Depending on the type of chromosome change, different malformations or clinical pictures can develop.

Children with defective genetic makeup

• The best known chromosome abnormality is trisomy 21 (Down syndrome). Trisomy 21 means that chromosome number 21 is present three times instead of only twice. The affected children are inhibited in their development and show malformations (such as heart defects) more often than other children.
• Children with other trisomies (for example three chromosomes No. 13 or 18) are either not viable at all or have a significantly lower life expectancy than healthy children and suffer from severe disabilities.
• If a fetus has the genetic make-up 45X0, this means that it lacks a sex chromosome. A girl then develops with the so-called Turner syndrome (Ullrich-Turner syndrome). Women with this hereditary disease are short, have a widened neck base (pterygium colli) and cannot have children. However, they are usually normally gifted.

Investigation and diagnosis of chromosomal abnormalities

The genetic makeup of the fetus can already be examined in the womb using various techniques:

• Amniocentesis (amniocentesis). The amniotic fluid removed with a fine hollow needle contains cells from the child that can be examined. Chemical analyzes also provide indications of a chromosomal disease.
• Placenta examination (chorionic villus sampling) from the placenta of the placenta (CVS)
• Umbilical cord puncture: ultrasound-controlled blood sampling from the umbilical cord and examination of the chromosome set of the child's blood cells
• Direct puncture of the fetus: direct removal of child's body cells or puncture of the urinary bladder under ultrasound control
• Blood tests for chromosomal abnormalities: You can determine a chromosomal abnormality in the unborn child with a high, but not 100% certainty. However, false-positive and false-negative findings are possible, which must then be further clarified by the above-mentioned examinations.

If there is reliable evidence of a chromosomal abnormality that leads to a severe disability in the child or is incompatible with life, the pregnancy can be terminated. An abortion should be carried out at the earliest possible point in time - after extensive advice from the parents.

Tags:  tcm anatomy palliative medicine