Down syndrome is usually caused by an error in cell division celled non-disjunction. However, two other types of chromosomal abnormalities, mosaicism and translocation, are also implicated in Down syndrome íV although to a much lesser extent. Regardless of the type of Down syndrome that a person may have, all people with Down syndrome have an extra critical portion of the number 21 chromosome present in all, or some, of their cells. This additional genetic material alters the course of development and causes the characteristics associated with the syndrome.
The diagnosis of Down syndrome is usually suspected after birth as a result of the baby's appearance. It is a particularly difficult time, coupled with the natural stresses of childbirth. Although there is no easy way to be informed, most families agree that having the baby present, being together and being told as soon as possible is the best way to proceed.
There are many physical characteristics which form the basis for suspecting an infant has Down syndrome. But many of these characteristics are found, to some extent, in the general population of individuals who do not have Down syndrome. If Down syndrome is suspected, a karyotype will be performed to ascertain the diagnosis. Some infants with Down syndrome have only a few of these traits, while others have many. Among the most common traits are:
- Muscle hypotonia, low muscle tone.
- Flat facial profile, a somewhat depressed nasal bridge and a small nose.
- Oblique palpebral fissures, an upward slant to the eyes.
- Dysplastic ear, an abnormal shape of the ear.
- A single deep crease across the center of the palm.
- Hyperflexibility, an excessive ability to extend the joins.
- Dysplastic middle phalanx of the fifth finger, fifth finger has one flexion furrow instead of two.
- Epicanthal folds, small skin folds on the inner corner of the eyes.
- Excessive space between large and second toe.
- Enlargement of tongue in relationship to size of mouth