Chromosomal aberrations are disruptions in the normal chromosomal content of a cell and are a major cause of genetic conditions in humans, such as Down syndrome, although most aberrations have little to no effect. Some chromosome abnormalities do not cause disease in carriers, such as translocations, or chromosomal inversions, although they may lead to a higher chance of bearing a child with a chromosome disorder. Abnormal numbers of chromosomes or chromosome sets, called aneuploidy, may be lethal or may give rise to genetic disorders. Genetic counseling is offered for families that may carry a chromosome rearrangement.
The gain or loss of DNA from chromosomes can lead to a variety of genetic disorders. Human examples include:
- Cri du chat, which is caused by the deletion of part of the short arm of chromosome 5. "Cri du chat" means "cry of the cat" in French; the condition was so-named because affected babies make high-pitched cries that sound like those of a cat. Affected individuals have wide-set eyes, a small head and jaw, moderate to severe mental health issues, and are very short.
- Down syndrome, the most common trisomy, usually caused by an extra copy of chromosome 21 (trisomy 21). Characteristics include decreased muscle tone, stockier build, asymmetrical skull, slanting eyes and mild to moderate developmental disability.
- Edwards syndrome, or trisomy-18, the second-most-common trisomy. Symptoms include motor retardation, developmental disability and numerous congenital anomalies causing serious health problems. Ninety percent of those affected die in infancy. They have characteristic clenched hands and overlapping fingers.
- Isodicentric 15, also called idic(15), partial tetrasomy 15q, or inverted duplication 15 (inv dup 15).
- Jacobsen syndrome, which is very rare. It is also called the terminal 11q deletion disorder. Those affected have normal intelligence or mild developmental disability, with poor expressive language skills. Most have a bleeding disorder called Paris-Trousseau syndrome.
- Klinefelter syndrome (XXY). Men with Klinefelter syndrome are usually sterile, and tend to be taller and have longer arms and legs than their peers. Boys with the syndrome are often shy and quiet, and have a higher incidence of speech delay and dyslexia. Without testosterone treatment, some may develop gynecomastia during puberty.
- Patau Syndrome, also called D-Syndrome or trisomy-13. Symptoms are somewhat similar to those of trisomy-18, without the characteristic folded hand.
- Small supernumerary marker chromosome. This means there is an extra, abnormal chromosome. Features depend on the origin of the extra genetic material. Cat-eye syndrome and isodicentric chromosome 15 syndrome (or Idic15) are both caused by a supernumerary marker chromosome, as is Pallister-Killian syndrome.
- Triple-X syndrome (XXX). XXX girls tend to be tall and thin and have a higher incidence of dyslexia.
- Turner syndrome (X instead of XX or XY). In Turner syndrome, female sexual characteristics are present but underdeveloped. Females with Turner syndrome often have a short stature, low hairline, abnormal eye features and bone development and a "caved-in" appearance to the chest.
- XYY syndrome. XYY boys are usually taller than their siblings. Like XXY boys and XXX girls, they are more likely to have learning difficulties.
- Wolf-Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4. It is characterized by severe growth retardation and severe to profound mental health issues.
Read more about this topic: Chromosome
Other articles related to "aberrations, aberration":
... Jealousy over the birth of a sibling, and resulting aggression, may also provoke tantrums over minor matters, in the effort to contain the major emotional upset ... Some people who have neurological disorders such as the combination of autism or mental retardation could be more prone to tantrums than others, although anyone experiencing forebrain damage (temporary or permanent) can suffer from tantrums ...
... Ocular aberrations are distortions in the wavefront passing through the pupil of the eye ... These aberrations diminish the quality of the image formed on the retina, sometimes necessitating the wearing of spectacles or contact lenses ... and contact lenses correct "low-order aberrations", such as defocus and astigmatism, which tend to be stable in humans for long periods of time (months or years) ...
... Chromosomal aberrations ... Reports of structural chromosome aberrations in people exposed to fallout in Belarus and other parts of the former Soviet Union, Austria, and Germany argue against a simple ... Inasmuch as some types of aberrations are almost specific for ionizing radiation, researchers use aberrations to assess exposure dose ...
... two or more chromosomes or by multiple aberrations within a single chromosome (e.g ... chromosome must be specified in parentheses followed by all aberrations involved in this derivative chromosome ... The aberrations must be listed from pter to qter and not be separated by a comma ...
... Shortcomings such as these in an optical system cause what are called optical aberrations ... The best-known aberrations include spherical aberration and coma ... However there may be more complex sources of aberrations such as in a large telescope due to spatial variations in the index of refraction of the atmosphere ...
Famous quotes containing the word aberrations:
“When people put their ballots in the boxes, they are, by that act, inoculated against the feeling that the government is not theirs. They then accept, in some measure, that its errors are their errors, its aberrations their aberrations, that any revolt will be against them. Its a remarkably shrewed and rather conservative arrangement when one thinks of it.”
—John Kenneth Galbraith (b. 1908)