Down Syndrome is a chromosomal disorder, that forms due to the inheritance of an extra chromosome 21.
Some of the most common symptoms of Down Syndrome are low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the centre of the palm. However, not every person who has Down Syndrome will experience the same level of these physical traits. Furthermore, Down Syndrome also impairs cognitive disability.
Individuals with Down syndrome have a higher risk of some diseases including Alzheimer’s and epilepsy.However, people with Down syndrome also have a lower risk of hardening of the arteries, diabetic retinopathy, and most kinds of cancer.
In fact, older women, usually over 40 are more likely to develop Down Syndrome. We are now able to detect whether a foetus has Down Syndrome by gene probing and genetic screening.
There are three types of Down Syndrome: trisomy 21, translocation and mosaicism.
Trisomy 21 is usually caused by nondisjunction which is an error in cell division. This is 95% of Down Syndrome cases, the inheritance of an extra chromosome 21.
Translocation occurs in around 4% of cases. In these cases there are still 46 chromosomes, but an additional full or partial copy of chromosome 21 attaches to another chromosome, usually chromosome 14. Resulting in the symptoms that accompany Down Syndrome.
Finally, mosaicism is the least common case of Down Syndrome and occurs in around 1% of cases. A mixture of two types of cells, some containing the usual 46 chromosomes and some containing 47 results in Down Syndrome in these individuals.
The causes of Down Syndrome are unknown however maternal age is a significant factor. But as younger women usually have more children, 80% of Down Syndrome children are born to children with mothers younger than 35. Around 5% of cases are traced back to the father and 14% of Down Syndrome cases are hereditary