MadSci Network: Genetics
Query:

Re: What happens when there is a deletion in one of the chromosomes 18?

Date: Sun Mar 27 23:21:58 2005
Posted By: Paul Nagami, Undergraduate, Biology, California Institute of Technology
Area of science: Genetics
ID: 1111777387.Ge
Message:

Although the complete loss of chromosome 18 results in abortion very 
early in pregnancy, the results of a smaller deletion will depend on its 
location and size.

Several tumor-suppressor genes occur on this chromosome, so some 
deletions would likely render patients more prone to cancer. In several 
types of tumor, and in particular colon cancer, deletions of chromosome 
18 are very common. So we have one effect there. [1]

If the short arm of chromosome 18 is lost, de Grouchy syndrome 1 (or 18p- 
syndrome) results. This is actually a pretty common deletion, and results 
in mental retardation (associated with a failure of the brain to furrow 
normally in the developing fetus), cleft palate, and other varying 
results. [2]

If, on the other hand, we lose the long arm of chromosome 18, we get de 
Grouchy syndrome 2 (18q- syndrome), which also leads to mental 
retardation. The symptoms vary, though, and may include growth 
retardation. [3]

I hope that this is helpful; the links below give much, much more 
thorough descriptions of the deletion syndromes.

Paul Nagami

References:

1. Jackson, KE et al. (2000) Phenotypic features in a boy with monosomy 
18 mosaicism. American Journal of Medical Genetics 95(3):229-232

2. "chromosome 18p deletion syndrome." (1999) Jablonski's Multiple 
Congenital Anomaly/Mental Retardation (MCA/MR) Syndromes Database, at the 
US National Library of Medicine website: http://www.nlm.nih.gov/mesh/jablonski/syndromes/syndrome192.html

3. "chromosome 18q deletion syndrome." (1999) Jablonski's Multiple 
Congenital Anomaly/Mental Retardation (MCA/MR) Syndromes Database, at the 
US National Library of Medicine website: http://www.nlm.nih.gov/cgi/jablonski/syndrome_cgi?index=194


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