Introduction – What is a chromosomal aberration?
A chromosomal aberration describes a deviation from the normal human chromosome configuration. A normal human chromosome set has 23 chromosome pairs of the same kind, which contain the entire genetic material. A chromosomal aberration can be both a numerical and a structural deviation of the chromosome set.
Chromosomal aberrations are the most common reason for a prenatal miscarriage. However, there are also viable forms of chromosomal aberrations, such as Down’s syndrome (trisomy 21) or Klinefelter’s syndrome (XXY syndrome). A chromosomal aberration can be recognized by the creation of a karyogram. This can be compared with a healthy karyogram, so that abnormalities are immediately noticeable.
What are numerical chromosome aberrations?
Numerical chromosomal aberrations describe a set of chromosomes that has a different number of chromosomes. Individual chromosomes may be duplicated or missing (aneuploidy) or the complete set of chromosomes may be duplicated (polyploidy). The best known and most widespread numerical chromosomal aberration is trisomy 21 (Down syndrome).
In this disease, the 21st chromosome is present in triplicate. The chance of giving birth to a child with trisomy 21 increases with the age of the mother. Children with Down’s syndrome fail: Mental retardation in particular varies greatly from patient to patient, so that individual treatment, support and care are paramount.
Life expectancy is only minimally reduced by trisomy 21. This is not the case with other trisomy forms, such as trisomy 13 ( syndrome) and trisomy 18 (Edwards syndrome), where life expectancy is less than one year. Other numerical chromosomal aberrations that affect the sex chromosomes are Klinefelter’s syndrome and Ullrich-Turner syndrome.
In Klinefelter syndrome, men are affected. They have two X chromosomes instead of one. The most prominent symptom is hypergrowth caused by testosterone deficiency.
In Turner’s syndrome, the affected women are missing an X chromosome. The lack of estrogen and progestin causes the ovaries to grow through connective tissue and the women remain infertile for life. In Turner syndrome, the affected women lack an X chromosome. The lack of oestrogen and progestin causes the ovaries to grow through connective tissue and the women remain infertile for life. – Dwarfism
- Four Finger Furrows
- Diagonally outward pulling (mongoloid) eyelid axes
- Reduced motor skills and intelligence
What are structural chromosome aberrations?
Structural chromosomal aberrations are deviations of chromosomes with respect to their structure. In contrast to numerical chromosomal aberrations, the normal number of chromosomes (23 homologous pairs, a total of 46 chromosomes) is retained. There are different forms of structural chromosomal aberrations, such as: In general, structural chromosomal aberrations are distinguished between a balanced and an unbalanced chromosomal alteration.
The balanced one has no disease value for the wearer, whereas the unbalanced one leads to physical symptoms. – DELETION: In deletion, a section of chromosomes is lost, and with it, part of the genetic material. An example of such a disease is the cat cry syndrome.
Such children are conspicuous by shrill screaming, are often undergrown, have weakly developed muscles and a small head. The Wolf-Hirschhorn-Syndrome is also caused by a deletion. A characteristic feature of this disease is the numerous epileptic attacks of the patients.
- TRANSLOCATION: Another structural chromosomal aberration is the translocation. In this case a chromosomal segment is shifted to another, non-homologous chromosome. A distinction is then also made between a reciprocal and a non-reciprocal translocation. – INVERSION: Inversion describes a structural chromosomal aberration in which a chromosomal segment is reversed.