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12 Feb 2004

handicapped and down syndrome
Hi what would cause a baby to be mentally handicapped? I have heard that a down syndrome baby has one extra gene, is that true. Please explain.
Answer 325 views
Expert
Geneticist
geneticist

01 Jan 0001

Dear Y

There are many different causes for abnormal pregnancies, some genetic (e.g. Down syndrome) and some environmental (e.g. infection). Down syndrome is indeed caused by an extra chromosome 21 (not gene), one of the smallest chromosomes in humans. Genes are carried on chromosomes so there are many genes on chromosome 21, and it is this duplication or extra copies (imbalance) that result in mentally handicapped babies due to imperfect cellular processes. Increased maternal age is one factor that may increase the risk of Down syndrome.

Regards, Maritha
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