Down syndrome, or trisomy 21, is a genetic disorder and chromosomal condition characterized by a third copy of chromosome 21. Normally, people are born with 46 chromosomes, but in a person with Down syndrome, 47 chromosomes are present.
The cause of Down syndrome is unknown, but risk factors for having a baby with Down syndrome include: being pregnant over the age of 35, having a sibling with Down syndrome, having a child with Down syndrome.
People with Down syndrome have distinctive features including a flat face, slanted eyes, and small ears and mouths. They also have shorter necks, arms, and legs than the norm.
In almost all cases, those with Down syndrome will have physical and mental disabilities. Adults with Down syndrome function intellectually at an 8- or 9-year-old level. They also have an increased risk for other health problems.
People with Down syndrome begin cognitive decline at an earlier age than those without. Typically, at around the age of 50, they will start to experience gradual loss of memory, judgement, and their ability to function. Approximately 50% of people with Down syndrome will develop Alzheimer's disease.