Down syndrome happens to a child before the child is born. Researchers don’t know what causes DS, beyond the extra 21st chromosome. Children born to mothers who are over 35 years of age are at a higher risk of developing DS; the child born to a 30-year old mother has a one in 900 chance of developing the condition while these odds have greatly increased to one in 350 in a mother who is 35. When the mother hits her 40th birthday, her chances of giving birth to a child with DS are now one in 100.
Children born with DS have the characteristic flat faces, rough hair, upward-slanting eyes, large, protruding tongues, small ears and low muscle tone, or hypotonia. These children do reach their developmental milestones, but they reach them later than their peers who do not have DS.
The low muscle tone issue may contribute to feeding problems and digestive issues. Children with DS have a “mild to moderate" intellectual impairment. These children are definitely capable of learning, but they learn at their own pace.
DS is not “catching," meaning siblings of the child with DS will not develop the condition just from being around their sibling. Learn more about Down syndrome by reading our Bright Hub guides.
Image Credit: http://www.freedigitalphotos.net/images/view_photog.php?photogid=721: Microscope Credit renjith krishnan