Estimates put the incidence of Down syndrome, or DS, at between 1 in 650 and 1 in 1000 of children born. The syndrome affects both the physical and mental abilities of those who are born with it.
How Down syndrome occurs
Down syndrome is named for John Langdon Brown, a British doctor who first described it in 1887.
The condition, also known as Trisomy 21, is caused by excess genetic material. A child normally inherits 23 chromosomes from each parent – 46 chromosomes in total. In children with Down syndrome, the child receives an extra chromosome for a total of 47 chromosomes. This extra chromosome is responsible for delays in the way the child develops and also for the distinct physical features seen in people with this condition.
Characteristics of people with Down syndrome
People with the syndrome normally share some physical characteristics: they have upwardly slanted eyes, small ears, a protruding tongue and a flat facial profile.
Low muscle tone is common among people with the condition and children with the syndrome typically reach their developmental milestones later than other children. They also generally grow slower than other children and are smaller than children of their age.
All people with Down syndrome have some intellectual impairment.
Medical problems associated with Down syndrome