A constellation of effects from the presence of all or part of an extra chromosome 21. (It is also called Trisomy 21 syndrome.) Characteristic findings are widely spaced first and second toes, a single hand (simian) crease, short fingers, a fold of tissue (epicanthal fold) across the inner aspect of the eye (near the nose), eyes that slant upward, decreased muscle tone, flattened back portion of the head, and a protruding tongue.
The only way to make the diagnosis with certainty is to perform a chromosomal analysis either before birth (through chorionic villus sampling or amniocentesis) or after birth (through blood or tissue chromosomal analysis).
The range of outcomes for Down syndrome children is quite broad, and many function quite well, although very few have normal intelligence.
The risk of a healthy woman having a child with Down syndrome increases with maternal age, as follows:
- 25 years: 1 in 1300
- 30 years: 1 in 900
- 35 years: 1 in 350
- 40 years: 1 in 100
- 45 years: 1 in 25
- 49 years: 1 in 12