Down's Syndrome

This is an example of trisomy.

Down's syndrome is one of the most common forms of chromosome abnormality in humans. Individuals with Down syndrome are typically mentally retarded, with a stocky body, stubby fingers, swollen tongue, peculiar eyelid folds and peculiar facial features. Many of them die in early childhood as a result of infections and heart defects.

Patients have an extra chromosome 21, and there are 47 chromosomes totally in the nucleus of each cell. The presence of an extra chromosome is due to non-disjunction of the 21st pair of homologous chromosomes in meiosis during gamete formation.

There is a relatively high incidence of Down syndrome among children born of mothers aged over 35, but the exact reason is unknown.


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(06.08.2008)