Down syndrome is the name for the pattern of physical features and disorders that usually occur from an extra 21st chromosome. Chromosomes are the materials that store people's genetic information.
Because people who have Down syndrome have an extra chromosome, the body's natural balance is upset. This upset in balance leads to various birth defects and problems of growth and development. Many of the birth defects in people who have Down syndrome are like those seen in other children. People with Down syndrome simply are likely to have birth defects more often than others.
The following characteristics can be seen in people with Down syndrome: smaller-than-average physical sizepoor muscle tone, which tends to improve somewhat over timea small head, the back of which is flatter than averageflat facial profileupward slant of the eye slitsan extra fold of skin at the inner corners of the eyessmall mouth with a tendency to protrude the tonguesmall hands with short fingers and a single crease across the palmscongenital heart disease, or heart defects that are present at birthlearning disabilitiesan IQ that is rarely higher than 50 (with normal IQ being around 100)faster aging process, with a tendency to develop diseases of aging, such as Alzheimer's disease, at a relatively early age
Down syndrome is usually caused by an extra 21st chromosome.
Most people have 46 chromosomes in each cell of their bodies. These chromosomes exist in pairs, for a total of 23 pairs. The pair associated with Down syndrome is called pair 21. Why an extra copy of this chromosome causes the features of the Down syndrome is not known.
The genetic material on the 21st chromosome pair directs the formation of compounds that the body needs to perform various functions and for normal development. The overload of information caused by the extra copy leads to the Down syndrome.
Scientists have recently identified 99.7% of the genes on this chromosome. This knowledge may lead to a better understanding of the syndrome and, perhaps, even treatments for some of the effects.
Down syndrome occurs in roughly 1 of every 1,000 births. There is a strong link between the risk of Down syndrome and the age of the mother. The risk of having a child with Down syndrome is less than 1 in 2,500 among young women. This risk increases to roughly 1 in 350 when women reach 35 years of age. After age 45, the risk is roughly 1 in 30.
Down syndrome is caused by a chromosome abnormality that is present when conception occurs. So there is no way to prevent Down syndrome.Genetic counseling is also useful for the families of affected children.
Down syndrome may be suspected at birth when certain physical features or defects are present. A chromosome analysis, however, confirms the diagnosis.
There are also tests that screen for Down syndrome during pregnancy. A blood test known as the triple screen measures the levels of certain chemicals in a pregnant woman's blood. These chemicals are estriol, human chorionic gonadotropin, and alpha-fetoprotein. When the chemicals are out of balance, there is a risk that the fetus has Down syndrome.
Other tests can be ordered to confirm the diagnosis of Down syndrome. These tests analyze the chromosomes of tissue taken from the unborn baby. These tests include chorionic villus sampling and amniocentesis.
People with Down syndrome are more at risk for some diseases and conditions, including: leukemiagastroesophageal reflux disease (GERD) and other digestive disordersfrequent ear infectionsdiabeteshypothyroidism, or a low level of thyroid hormonelung infections, such as pneumoniaAlzheimer's disease, which causes memory loss and impaired thinking
The life span for people with Down syndrome is shorter than average. Congenital heart disease is the leading cause of death in infants with Down syndrome. Otherwise, 3 of 4 people with Down syndrome reach 30 to 35 years of age.
Common causes of death in older individuals include lung disease, other infections, hepatitis, and leukemia, a cancer of the blood. Chronic infections of the eyes and nose, tooth disease, and thyroid gland problems are common at all ages.
Down syndrome is not contagious. Males with Down syndrome have not been known to have children and females rarely do. Therefore, the disorder usually is not passed from one affected person to another.
Possibly because of genetic reasons, parents who have had one affected child are at slightly higher risk than others to have another affected child. In some cases, the risk may be much higher if the parents have certain genetic problems. For this reason, genetic counseling for families of people with Down syndrome may be helpful.
There is no treatment for the Down syndrome itself. Treatment is directed toward whatever health and other problems affected people may have. Education strategies, occupational therapy, physical therapy, and early intervention services all may be helpful.
Side effects depend upon the treatment used. Open heart surgery, for example, has more side effects than treatment of ear infections.
In general, people who have Down syndrome function well in society. With good support systems, most can live fairly normal, productive lives.
Down syndrome does not get worse, except for the aging process mentioned earlier. Health screening for children and adults with Down syndrome involves regular hearing tests, thyroid function tests, eye tests, and follow-up for diagnosed health problems. Any new or worsening symptoms should be reported to the healthcare professional.
Jones KL: Recognizable Patterns of Human Malformation. WB Saunders, 1997.