Trisomy 21
Key points
- Down syndrome is a chromosome abnormality, usually due to an extra copy of the 21st chromosome.
- In most cases, Down syndrome is caused by an extra chromosome 21.
- A heart murmur may be revealed by listening to the chest with a stethoscope.
- The normal life span is shortened in Down syndrome by congenital heart disease and by increased incidence of acute leukemia.
Alternative names
Down syndrome
Definition
Down syndrome is a chromosome abnormality, usually due to an extra copy of the 21st chromosome. This syndrome usually, although not always, results in mental retardation and other conditions.
Causes, incidence, and risk factors
In most cases, Down syndrome is caused by an extra chromosome 21. It is the most common single cause of human birth defects, with an occurence in 1 out of every 660 births.
Children with Down syndrome have a widely recognized characteristic appearance. The head may be smaller than normal (microcephaly) and abnormally shaped. Prominent facial features include a flattened nose, protruding tongue, and upward slanting eyes. The inner corner of the eyes may have a rounded fold of skin (epicanthal fold) rather than coming to a point. The hands are short and broad with short fingers and often have a single crease in the palm (simian crease). Retardation of normal growth and development is typical and most affected children never reach average adult height.
Congenital heart defects are frequently present in Down syndrome children. Early mortality is often a result of cardiac abnormalities. Gastrointestinal abnormalities such as esophageal atresia (obstruction of the esophagus) and duodenal atresia (obstruction of the duodenum) are also relatively common. Obstruction of the gastrointestinal tract may require major surgery shortly after birth. Children with Down syndrome also have a higher than average incidence of acute lymphocytic leukemia (ALL).
Symptoms
- Decreased muscle tone at birth
- Separated sutures (joints between the bones of the skull)
- Asymmetrical or odd-shaped skull
o Round head with flat area at the back of the head (occiput)
o Small skull (microcephaly) - Upward slanting eyes, unusual for ethnic group
- Small mouth with protruding tongue (see tongue problems)
- Broad short hands
- Single crease on the palm
- Retarded growth and development
- Delayed mental and social skills (mental retardation)
- Iris lesion (an abnormality of the colored part of the eye called Brushfield spots)
Signs and tests
A heart murmur may be revealed by listening to the chest with a stethoscope. Characteristic abnormalities are revealed by a physical examination. These include a flattened facial profile, small ears, separation of the abdominal muscles, joint hyperflexibility, awkward gait, extra skin on back of neck at birth, and an abnormal bone in the middle of the 5th finger.
Written and revised by
Andrey Nailor, M.D.
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