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Down Syndrome (Trisomy 21) [Q90]

OMIM number: 190685

Dipl.-Biol. Uwe Heinrich

Scientific Background

The Down syndrome is caused by an additional chromosome 21 (trisomy 21). Life expectancy has risen significantly during the last few years; however, it is 20 years less compared to the general population. Clinical signs are intellectual disability, typical facial features (epicanthal fold, upslanting palpebral fissures, macroglossia), cardiac defect, muscle hypotonia, sandal gap and single transverse palmar crease. Women with Down syndrome are fertile, men usually infertile. A high susceptability for infections as well as a slightly elevated risk for leukemia during childhood are characteristic for the Down syndrome.

There is very good support available for patients with Down syndrome, which is aiming at providing a high level of independence in their adulthood. However, most adults suffering from Down syndrome depend on support in their daily lives. On average, the Down syndrome has an incidence of 1:650 newborns, with a maternal age effect (1:1,250 in a 20-year-old, 1:90 in a 40-year-old woman) playing a role. In 92% of all patients, an additional chromosome 21 is present (free trisomy), in 3% a mosaic trisomy 21, and 5% exhibit what is called a Robertsonian translocation between a third chromosome 21 and an acrocentric chromosome (known as hereditary Down syndrome). In very rare cases, Down syndrome may result from partial trisomies due to other translocations.