Downs syndrome means a physicl anabnormalities .Down syndrome is caused by a random error in cell division that results in the presence of an extra copy of chromosome 21.in more than 90% of cases, the extra copy of chromosome 21 comes from the mother in the egg.In about 4% of the cases, the father provides the extra copy of chromosome 21 through the sperm.In the remaining cases, the error occurs after fertilization, as the embryo grows.
Down syndrome is a chromosomal condition that is associated with intellectual disability, a characteristic facial appearance, and weak muscle tone (hypotonia) in infancy. All affected individuals experience cognitive delays, but the intellectual disability is usually mild to moderate.
Down syndrome is the most frequent chromosomal cause of mild to moderate intellectual disability, and it occurs in all ethnic and economic groups. Currently, more than 400,000 people are living with Down syndrome in the United States, according to the National Down Syndrome Society.
n the United States, demographic factors also affect the risk for a child to be born with Down syndrome. These factors include geographic region, maternal education, marital status, and Hispanic ethnicity.