Down syndrome encompasses a number of genetic disorders, of which trisomy 21 (a non disjunction) is the most representative, causing highly variable degrees of learning difficulties as well as physical disabilities. It is named for John Langdon Down, the British doctor who first described it in the late 19th century.trisomy 21 (British Down's syndrome) is a genetic condition resulting from the presence of all or part of an extra 21st chromosome. Down syndrome is characterized by a combination of major and minor abnormalities of body structure and function. Among features present in nearly all cases are impairment of learning and physical growth, and a recognizable facial appearance usually identified at birth. It is named after John Langdon Down, the British doctor who first described it in 1866.
Individuals with Down syndrome have lower than average cognitive ability, normally ranging from mild to moderate retardation. Some individuals may have low intelligence overall, but will generally have some amount of developmental disability, such as a tendency toward concrete thinking or naïveté. There is also a small number of individuals with Down syndrome with severe to profound mental retardation. The incidence of Down syndrome is estimated at 1 per 800 to 1 per 1000 births.
The common physical features of Down syndrome also appear in people with a standard set of chromosomes. They include a simian crease (a single crease across one or both palms), almond shaped eyes, shorter limbs, speech impairment, and protruding tongue. Health concerns for individuals with Down syndrome include a higher risk for congenital heart defects, gastroesophageal reflux disease, recurrent ear infections, obstructive sleep apnea, and thyroid dysfunctions.
Early childhood intervention, screening for common problems, medical treatment where indicated, a conducive family environment, and vocational training can improve the overall development of children with Down syndrome. While some of the genetic limitations of Down Syndrome cannot be overcome, education and proper care, initiated at any time, can improve quality of life.