A chromosomal aberration is an abnormality in the structure or number of chromosomes in an organism. Depending on the nature of the aberration, it can lead to severe birth defects, potentially including defects incompatible with life. Chromosomal aberrations can be diagnosed with the use of a karyotype, a visualization of an organism's complete set of chromosomes, where functional changes in the chromosomes will be readily visible. Treatment for people with chromosomal aberrations involves the provision of supportive care, as it is not possible to cure conditions caused by problems with the chromosomes.
The cause of a chromosomal aberration is usually a problem during cell division, either when cells divide to make gametes used in reproduction, or when cells are in the process of dividing in the embryonic state. Exposure to radioactive substances and chemicals known to cause mutations can cause abnormalities in the gametes that will be passed on to embryos in the event those gametes are used in fertilization. If errors occur during embryonic cell division, the resulting organism will exhibit genetic mosaicism, where some of the cells have a healthy set of chromosomes, and others display a chromosomal aberration.
Numerically, it is possible for a person to have three sets of chromosomes instead of two in one or more cases, creating an uneven number of total chromosomes. Conversely, a single chromosome instead of a pair may appear at one or more locations. The nature of the impairments experienced as a result of this type of chromosomal aberration vary; a well-known example of a numerical chromosomal aberration is Down Syndrome, where people have an extra 21st chromosome.
Structurally, chromosomal aberrations can include deletions, insertions, rings, inversions, translocations, and duplications. These may lead to a variety of birth defects and in some cases, a person may not have any noticeable symptoms because the aberration is minor. All of these aberrations can potentially be passed on to descendants, depending on what happens during cell division. In some cases, chromosomal aberrations render people effectively sterile.
Some chromosomal aberrations can be identified during pregnancy. An embryo may fail to develop as expected, leading to a diagnosis, or prenatal testing could provide information about genetic conditions. In some cases, these conditions lead to fetal death and a woman miscarries or experiences a stillbirth. People who experience pregnancy loss as a result of chromosomal aberrations may want to consider genetic testing to learn more about the risk of problems with future pregnancies.