trisomy 21 (usually Down's Syndrome in British English[1]) is a genetic disorder caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British doctor who described it in 1866. The disorder was identified as a chromosome 21 trisomy by Jérôme Lejeune [1] in 1959. The condition is characterized by a combination of major and minor differences in body structure. Often Down syndrome is associated with some impairment of cognitive ability and physical growth as well as facial appearance. Down syndrome can be identified during pregnancy or at birth. Individuals with Down syndrome can have a lower than average cognitive ability, often ranging from mild to moderate mental retardation. Developmental disabilities often manifest as a tendency toward concrete thinking or naïveté. A small number have severe to profound mental retardation. The incidence of Down syndrome is estimated at 1 per 800 to 1,000 births.
Many of the common physical features of Down syndrome also appear in people with a standard set of chromosomes. They include a single transverse palmar crease (a single instead of a double crease across one or both palms), an almond shape to the eyes caused by an epicanthic fold of the eyelid, shorter limbs, poor muscle tone, a larger than normal space between the big and second toes, 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. Although some of the physical genetic limitations of Down syndrome cannot be overcome, education and proper care will improve quality of life. These resources are available through your local county office and are usually given to the parent upon learning that their child has Down Syndrome.
