Etiology of Chromosome Abnormalities

Etiology of chromosome abnormalities is pretty variable. The most often reason is mistake which occurs during the cell division. It is connected with wrong development of the sperm or ovum (female reproduction cell). We recognize two types of cell division – mitosis and meiosis. Another causes are the maternal age and the ifluence of the enviromental.

Chromosome abnormalities are usually fatal. Each second first-trimester abortion is caused by them. Children who survive and get born suffer from very serious mental and physical problems. The screening for chromosome abnormalities is very important. The cytogeneticists use the karyotype testing.

Problems in the Cell Division
We recognize two main types of the cell divison. The first one is the meiosis. It is the process of division of reproduction cells. The result is a cell with 23 chromosomes (it is haploid). Fetus get 23 chromosomes from the mother and 23 chromosomes from the father. Cells of fetus are already diploid (2N). Mistake during meiosis leads to incorrect number of the chromosomes in the egg or in the sperm. Child can get some extra chromosome (trisomy) or miss it (monosomy).

The second type of cell division is the mitosis. It occurs in all non-reproductive cells. It is a form of duplication of the genetic information, followed by the halving of material. The parent cell has 92 chromosomes (4N), two subsidiary cells have 46 chromosome each (2N). Mitosis starts immediately after fertilization and continues throught whole life. When mistake occurs, the chromosomes may not be equal. Problems in mitosis leads to the mosaicism more often.

Age of Parents
We are sure about the strong influence of the maternal age (especially in Down syndrome). The paternal age is less important, but still has its importance. The difference is in cell division of reproduction cells. The number of eggs (female´s cells) is done by our birth. So eggs underway meiosis many times. The later age of delivery means the higher risk of some abnormalities. It takes just 72 hours to the developement of sperm cells. It is less propably to make a mistake during this period.

To the older women is recommended to visit some genetic counseling centre. "The older women" means more than 35 years. The prenatal diagnosis is the best way to find some affected children. The method of prenatal diagnosis as an amniocentesis.

Influence of the Environmental
It is very hard to tell how important is the enviromental. We can´t find any significant differences between parents with child with a chromosome abnormality and parents with healthy child. They have usually very similar lifestyle or habits. But there are still some dangerous influences – X-rays, medication or food. Most of them have a cumulative character.

Because we are not sure about the origin of abnormalities, it is hard to recommend any prevention. Sometimes it is said that the folic acid has a positive role in prevention of congenital abnormalities. Pregnant women should also get vitamines to reduce risks.



Related articles

 * Chromosome abnormalities
 * Karyotype
 * Autosomal disorders
 * Genetic Counseling
 * Meiosis
 * Mitosis