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What causes chromosomal disorders?

Chromosomal abnormalities are caused by errors in the number or structure of chromosomes. These errors in the number of chromosomes occur during cell division. There are two kinds of cell division.

  • Mitosis results in two cells that are duplicates of the original cell. This kind of cell division occurs throughout the body, except in the reproductive organs. This is how most of the cells that make up the body are made and replaced.
  • Meiosis results in cells with half the number of chromosomes, 23 instead of the normal 46. These are the eggs and sperm.

In both processes, the correct number of chromosomes is supposed to end up in the resulting cells. However, errors in cell division can result in cells with too few or too many copies of a chromosome. Errors can also occur when the chromosomes are being duplicated, resulting in some cells with the correct number of chromosomes and some with an incorrect number of chromosomes. This results in a condition known as mosaicism.

The other cause of chromosomal abnormalities is an error in structure. These errors can occur before fertilization and alter the structure of one or more chromosomes. Individuals with structural chromosomal abnormalities usually have the normal number of chromosomes but, small pieces of a chromosome (or chromosomes) may be deleted, duplicated, inverted, misplaced or exchanged with part of another chromosome. These structural rearrangements may have no effect on a person if all of the chromosome is there but just rearranged. In other cases, the rearrangement may result a net loss or gain of chromosomal material and lead to pregnancy loss or congenital anomalies.

Chromosomal disorders are generally caused by mutations that affect a specific chromosome. Typically, these types of disorders are not inherited but are more likely random genetic errors that occur during the reproductive process. During cell division, a developing infant's body can mistakenly produce extra chromosomes or accidentally produce too few chromosomes. Sometimes the actual structure of a chromosome may be made incorrectly, and a chromosome may be missing a part. It's unclear what causes the mutations to occur.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.