Trisomy 21 also known as Down syndrome. it is a genetic disorder caused by the presence of a third copy of chromosome 21. It delays physical growth, characteristic facial features, and intellectual disability. The average IQ of a young adult with Down syndrome is 50, the parents of the affected individual are typically genetically normal. Down syndrome can be identified during pregnancy by prenatal screening followed by diagnostic testing or after birth by direct observation and genetic testing. Since the introduction of screening, pregnancies with the diagnosis are often terminated.
Those with Down syndrome have physical and intellectual disabilities, poor immune function. They have an increased risk of a number of other health problems, including congenital heart defect, epilepsy, leukemia, thyroid diseases, and mental disorders. There is no cure for Down syndrome