Down syndrome causes

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Down's syndrome is caused by triplication of chromosome 21 (trisomy 21). The aneuploidy may occur in three possible ways:

Meiotic nondisjunction of homologous chromosomes
- From improper division of chromosomes during meiosis I or meiosis II. One gamete will end up with extra 21st chromosome.^[1]^[2]
Robertsonian translocation
- Individuals with normal number of chromosomes but an extra portion of 21st chromosome.
Mosaicism
- Post-fertilization mitotic error

For a detailed description on the mechanisms leading to Down's syndrome, click here

↑ Antonarakis SE (March 1991). "Parental origin of the extra chromosome in trisomy 21 as indicated by analysis of DNA polymorphisms. Down Syndrome Collaborative Group". N. Engl. J. Med. 324 (13): 872–6. doi:10.1056/NEJM199103283241302. PMID 1825697.
↑ Antonarakis SE, Petersen MB, McInnis MG, Adelsberger PA, Schinzel AA, Binkert F, Pangalos C, Raoul O, Slaugenhaupt SA, Hafez M (March 1992). "The meiotic stage of nondisjunction in trisomy 21: determination by using DNA polymorphisms". Am. J. Hum. Genet. 50 (3): 544–50. PMC 1684265. PMID 1347192.