Down syndrome is caused by trisomy 21 — the
person has three copies of chromosome 21, instead of the usual two
copies, in all cells. This is caused by abnormal cell division
during the development of the sperm cell or the egg cell.
Risk factors
- Advancing maternal age. A woman's chancesof
giving birth to a child with Down syndromeincrease
with age because older eggs have a greater risk of
improper chromosome division
further characteristics that the child may show as he gets
older.
- Heart defects. About half the children with
Down syndrome are born with some type of congenital heart defect.
These heart problems can be life-threatening and may require
surgery in early infancy.
- Gastrointestinal (GI) defects. GI
abnormalities occur in some children with Down syndrome and may
include abnormalities of the intestines, esophagus, trachea and
anus. The risk of developing digestive problems, such as GI
blockage, heartburn (gastroesophageal reflux) or celiac disease,
may be increased.
- Immune disorders. Because of abnormalities in
their immune systems, people with Down syndrome are at increased
risk of developing autoimmune disorders, some forms of cancer, and
infectious diseases, such as pneumonia.
- Sleep apnea. Because of soft tissue and
skeletal changes that lead to the obstruction of their airways,
children and adults with Down syndrome are at greater risk of
obstructive sleep apnea.
- Obesity. People with Down syndrome have a
greater tendency to be obese compared with the general
population.
- Spinal problems. Some people with Down
syndrome may have a misalignment of the top two vertebrae in the
neck (atlantoaxial instability). This condition puts them at risk
of serious injury to the spinal cord from overextension of the
neck.
- Leukemia. Young children with Down syndrome
have an increased risk of leukemia.
- Dementia. People with Down syndrome have a
greatly increased risk of dementia — signs and symptoms may begin
around age 50. Having Down syndrome also increases the risk of
developing Alzheimer's disease.
- Other problems. Down syndrome may also be
associated with other health conditions, including endocrine
problems, dental problems, seizures, ear infections, and hearing
and vision problems.