Chromosome abnormality

The three major single chromosome mutations; deletion (1), duplication (2) and inversion (3).
The two major two chromosome mutations; insertion (1) and Translocation (2).

A chromosome anomaly, abnormality, aberration, or mutation is a missing, extra, or irregular portion of chromosomal DNA.[1] It can be from an atypical number of chromosomes or a structural abnormality in one or more chromosomes. Chromosome mutation was formerly used in a strict sense to mean a change in a chromosomal segment, involving more than one gene.[2] A karyotype refers to a full set of chromosomes from an individual that can be compared to a "normal" karyotype for the species via genetic testing. A chromosome anomaly may be detected or confirmed in this manner. Chromosome anomalies usually occur when there is an error in cell division following meiosis or mitosis. There are many types of chromosome anomalies. They can be organized into two basic groups, numerical and structural anomalies.

Numerical disorders

This is called aneuploidy (an abnormal number of chromosomes), and occurs when an individual either is missing a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy, tetrasomy, etc.).

In humans, an example of a condition caused by a numerical anomaly is Down Syndrome, also known as Trisomy 21 (an individual with Down Syndrome has three copies of chromosome 21, rather than two). The frequency of Trisomy 21 has been determined to be a function of maternal age.

An example of monosomy is Turner syndrome, where the individual is born with only one sex chromosome, an X.

Sperm aneuploidy

Exposure of males to certain lifestyle, environmental and/or occupational hazards may increase the risk of aneuploid spermatozoa.[3] In particular, risk of aneuploidy is increased by tobacco smoking,[4][5] and occupational exposure to benzene,[6] insecticides,[7][8] and perfluorinated compounds.[9] Increased aneuploidy is often associated with increased DNA damage in spermatozoa.

Structural abnormalities

When the chromosome's structure is altered, this can take several forms:[10]

Chromosome instability syndromes are a group of disorders characterized by chromosomal instability and breakage. They often lead to an increased tendency to develop certain types of malignancies.

Inheritance

Most chromosome abnormalities occur as an accident in the egg cell or sperm, and therefore the anomaly is present in every cell of the body. Some anomalies, however, can happen after conception, resulting in Mosaicism (where some cells have the anomaly and some do not). Chromosome anomalies can be inherited from a parent or be "de novo". This is why chromosome studies are often performed on parents when a child is found to have an anomaly. If the parents do not possess the abnormality it was not initially inherited; however it may be transmitted to subsequent generations.

Acquired chromosome abnormalities

Most cancers, if not all, could cause chromosome abnormalities,[11] with either the formation of hybrid genes and fusion proteins, deregulation of genes and overexpresson of proteins, or loss of tumor suppressor genes (see the "Mitelman Database" [12] and the Atlas of Genetics and Cytogenetics in Oncology and Haematology,[13]).

See also

References

  1. ↑ NHGRI. 2006. Chromosome Abnormalities
  2. ↑ Rieger, R.; Michaelis, A.; Green, M.M. (1968). "Mutation". A glossary of genetics and cytogenetics: Classical and molecular. New York: Springer-Verlag. ISBN 9780387076683.
  3. ↑ Templado C, Uroz L, Estop A (2013). "New insights on the origin and relevance of aneuploidy in human spermatozoa". Mol. Hum. Reprod. 19 (10): 634–43. doi:10.1093/molehr/gat039. PMID 23720770.
  4. ↑ Shi Q, Ko E, Barclay L, Hoang T, Rademaker A, Martin R (2001). "Cigarette smoking and aneuploidy in human sperm". Mol. Reprod. Dev. 59 (4): 417–21. doi:10.1002/mrd.1048. PMID 11468778.
  5. ↑ Rubes J, Lowe X, Moore D, Perreault S, Slott V, Evenson D, Selevan SG, Wyrobek AJ (1998). "Smoking cigarettes is associated with increased sperm disomy in teenage men". Fertil. Steril. 70 (4): 715–23. PMID 9797104.
  6. ↑ Xing C, Marchetti F, Li G, Weldon RH, Kurtovich E, Young S, Schmid TE, Zhang L, Rappaport S, Waidyanatha S, Wyrobek AJ, Eskenazi B (2010). "Benzene exposure near the U.S. permissible limit is associated with sperm aneuploidy". Environ. Health Perspect. 118 (6): 833–9. doi:10.1289/ehp.0901531. PMC 2898861. PMID 20418200.
  7. ↑ Xia Y, Bian Q, Xu L, Cheng S, Song L, Liu J, Wu W, Wang S, Wang X (2004). "Genotoxic effects on human spermatozoa among pesticide factory workers exposed to fenvalerate". Toxicology 203 (1-3): 49–60. doi:10.1016/j.tox.2004.05.018. PMID 15363581.
  8. ↑ Xia Y, Cheng S, Bian Q, Xu L, Collins MD, Chang HC, Song L, Liu J, Wang S, Wang X (2005). "Genotoxic effects on spermatozoa of carbaryl-exposed workers". Toxicol. Sci. 85 (1): 615–23. doi:10.1093/toxsci/kfi066. PMID 15615886.
  9. ↑ Governini L, Guerranti C, De Leo V, Boschi L, Luddi A, Gori M, Orvieto R, Piomboni P (2014). "Chromosomal aneuploidies and DNA fragmentation of human spermatozoa from patients exposed to perfluorinated compounds". Andrologia 47: 1012–9. doi:10.1111/and.12371. PMID 25382683.
  10. ↑ http://atlasgeneticsoncology.org/Educ/PolyMecaEng.html
  11. ↑ http://atlasgeneticsoncology.org/Educ/Hempat_e.html
  12. ↑ "Mitelman Database of Chromosome Aberrations and Gene Fusions in Cancer".
  13. ↑ "Atlas of Genetics and Cytogenetics in Oncology and Haematology". atlasgeneticsoncology.org.

External links

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