Genetic Testing Guide Down Syndrome Genetic Testing Basics What
is Down syndrome? Down syndrome, a condition that is present at
birth, affects the body's physical and mental development. While
no two people with Down syndrome are exactly alike, they do
share some common physical features. Babies with Down syndrome
have similar facial features, tend to have lower muscle tone,
and typically learn to walk and talk slightly later than other
children. A person with Down syndrome typically has a slightly
small head that is flattened in the back; up-slanted eyes; extra
skin folds at the inner corners of the eyes; small ears, nose
and mouth; short stature; small hands and feet; and some degree
of intellectual disability. Normally, a child inherits two
copies of chromosome 21 one from each parent. If a child
inherits an extra chromosome 21, the child will have Down
syndrome. Because Down syndrome usually affects every cell in
the body, people can have a variety of medical problems. For
example, about 40% of children w