What is Down syndrome?
Down syndrome is a genetic condition caused by extra material from chromosome 21. It occurs in one out of every 700 births, among all cultures and economic levels. Individuals with Down syndrome have mild to moderate intellectual disabilities, low muscle tone, characteristic facial features and are at higher risk for a variety of health problems. Almost half of all people with Down syndrome have a heart defect.
Down syndrome typically occurs from a misdivision (nondisjunction) of the chromosome during the formation of the egg (or sometimes the sperm) that results in an extra chromosome 21. Individuals with nondisjunction Down syndrome have a total of 47 chromosomes, rather than the normal 46, with a whole additional chromosome 21. This type of Down syndrome tends to happen more often as a woman gets older, but can happen at any age. There is nothing a woman can do to cause or prevent Down syndrome from happening. Over 95% of cases of Down syndrome occur from nondisjunction and are not inherited in families. Approximately 3-4% of cases can result from a chromosome rearrangement (called a translocation) that may increase the risk for recurrence in other family members. Finally, 1-2% of cases are mosaic, which means the individual has a mixture of both normal cells and cells with an extra chromosome 21.
People with Down syndrome experience both intellectual and physical challenges, however, when provided appropriate education and health care, many live full lives forming meaningful relationships. Healthcare guidelines for individuals with Down syndrome are available. With implementation of these guidelines, the average lifespan for a person with Down syndrome has increased from an average of 25 years of age in 1983 to almost 60 years of age now.
How is the condition diagnosed?
Chromosome analysis (karyotype) is the only way to definitively make a diagnosis of Down syndrome. Typically, individuals have a total of 46 chromosomes or 23 pairs of chromosomes (2 of each set). Most people with Down syndrome have 47 chromosomes instead, with three copies of the 21st set of chromosomes rather than the typical two. Chromosome analysis can diagnose nondisjunction Down syndrome, translocation Down syndrome and mosaic Down syndrome.
There are two different ways to evaluate the chromosomes during pregnancy for a definite diagnosis. Chorionic villus sampling (CVS) is an invasive procedure that is performed between 10 and 13 weeks of pregnancy. It involves extraction of a sample of placenta to be used for chromosomal analysis. Amniocentesis is a second invasive procedure that can be performed after 15 weeks of pregnancy. It involves insertion of a needle into the uterus to extract fluid from around the fetus to be used for genetic studies. Both of these procedures carry a small risk for miscarriage of the pregnancy due to their invasive nature.
Screening for Down syndrome is available to all pregnant women. An ultrasound can be performed between 11 and 14 weeks gestation to evaluate an area behind the fetus’ neck called the nuchal translucency (NT). The NT is increased in about 70% of cases of Down syndrome. This ultrasound measurement can be combined with other ultrasound markers and maternal blood work to increase the detection rate to 85-90%. It should be noted that both false positive and false negative results occur with any screening test.
Second trimester screening is also available for Down syndrome. A maternal serum quad screen evaluates both hormones and proteins produced during pregnancy and can detect approximately 80% affected with Down syndrome. Level II ultrasound between 20-22 weeks gestation is also used to evaluate signs or symptoms associated with Down syndrome, such as heart defects. Ultrasound examination in the second trimester can detect over half of all pregnancies with Down syndrome.
Finally, Down syndrome can be diagnosed following birth by recognition of the characteristic facial features seen with the condition and confirmed with blood chromosome analysis.
How is Down syndrome treated?
There is no cure for Down syndrome, but medical care is available for any birth defects associated with the condition. Since heart defects are common with Down syndrome, evaluation with a pediatric Cardiologist is recommended either pre or postnatally. Newborns are also evaluated for feeding and digestive problems (such as duodenal atresia, constipation and Hirschsprung disease), congenital hearing loss or vision problems, hypothyroidism and respiratory tract infections. Healthcare guidelines with check lists are available from newborn to adulthood. Follow-up visits with a variety of specialists is sometimes necessary, dependent upon the child’s unique healthcare concerns.
Since some degree of intellectual disability is present for all people with Down syndrome, early intervention is recommended. These are state-funded programs that provide therapies for all children with developmental disabilities. It is known that speech therapy, occupational therapy and physical therapy services increase functioning and improve cognition for those with Down syndrome.
How will Down syndrome affect my baby after delivery?
Again, Down syndrome is present for life, but many children and adults with the condition lead full, healthy lives. The federal Individuals with Disabilities Education Act assures children with Down syndrome the right to a free and appropriate education in the public school system. Some young adults with Down syndrome are able to live outside the primary household, obtain driver’s licenses, attend post secondary education, get married and maintain gainful employment. However, others with Down syndrome continue to have difficulty with basic life skills into adulthood and remain dependent throughout their lifetime. There is no way to predict how well any one person with Down syndrome will function.
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