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In 1887 Landon-Down described a syndrome of mental handicap associated with
various physical abnormalities and a supposed resemblance to members of the Mongol
race. This unfortunately led to this condition becoming known as mongolism but
the condition is now known as Down's syndrome or trisomy 21.
Down's syndrome is the commonest of the chromosomal disorders and a major
cause of mental retardation. The incidence is approximately 1 in 700 births
(1).
The incidence of Down's syndrome, as with other trisomic abnormalities, increases
with maternal age. In the last decade the number of live births to women aged
40+ has doubled, with a 6% increase in fertility seen in 2006 (2). Note however
that mothers of any age can have infants with Down's syndrome and the majority
of Down's syndrome babies are born to younger mothers.
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