Down syndrome occurs when an extra chromosome is present in the genetic material of an embryo, usually resulting in developmental delay and leading to mental retardation and other abnormalities. Down syndrome affects one in every 800 babies born in the United States and is the single leading cause of birth defects.
At conception, the fetus inherits genetic information in the form of 46 chromosomes - 23 from each parent. Chromosomes contain protein and DNA, which controls the development of the fetus. Down syndrome results when an extra copy of the 21st chromosome is present.
Causes of Down Syndrome
The exact cause of the occasional appearance of an extra chromosome is unknown. What is known is that there is an increased risk of a fetus developing the disorder if the mother is over the age of thirty-five. The incidence of giving birth to a baby with Down syndrome at the age of thirty is one in 1,000; at the age of thirty-five, this risk jumps to 1 in 400. If the mother is 42 years old, this figure jumps dramatically, to 1 in 60.
Having one child with Down syndrome increases the risk of giving birth to a second child with Down syndrome.
Down Syndrome Effects: Characteristics and Symptoms of Down Syndrome
Down syndrome symptoms vary, as the disease can range from mild to severe manifestations. Common characteristics include:
- flat facial profile
- asymmetrical or oddly shaped skull
- upward slanting eyes
- enlarged tongue
- small ears
- broad, short hands
- decreased muscle tone
- delayed growth
- delayed mental and social skills
The above symptoms can have a variety of consequences for kids with Down syndrome. For example, decreased muscle tone can lead to developmental problems, and children may have problems sitting up, crawling and walking.
A child with Down syndrome may also have problems sucking or feeding, as well as digestion problems and constipation.
Children with Down syndrome may be average in size, but they grow more slowly. They can have speech problems and problems with self-care, such as dressing themselves and potty training.
Down syndrome can also impact a childï¿½s cognitive abilities, and while this effect can vary, it usually means that children with Down syndrome learn more slowly than children who do not have the disease.
Half of kids with Down syndrome have congenital heart defects, as well as problems with vision and hearing, and thyroid problems. Children with Down syndrome also often have respiratory problems and are more prone to infection, such as ear infections. They also have an increased risk of developing childhood leukemia.
Complications arising from Down syndrome can reduce a childï¿½s lifespan because of an increased rate of incidence of disease and leukemia.
Testing for Down Syndrome
Down syndrome can be diagnosed through either a screening test or a diagnostic test, both of which are conducted prior to birth.
Screening tests estimate the risk that a fetusï¿½s will be born Down syndrome. Tests include:
- Detailed ultrasound: this type of testing is 60% accurate in detecting the disease
- Triple screen: performed between 15 and 20 weeks of pregnancy, examines characteristics such as blood and age of the mother
- Nuchal translucency testing: performed between 11 and 14 weeks of pregnancy, measures the clear space in the tissue folds behind the neck. In fetuses with Down syndrome, fluid often builds up here. This method of testing is 80% accurate
Diagnostic testing determines whether the fetus actually has Down syndrome. Diagnostic testing for Down syndrome includes:
- Amniocentesis: performed at 16 to 20 weeks of pregnancy, amniotic fluid is removed and studied for chromosomal irregularities; risks include miscarriage and other pregnancy complications
- Choronic vilius sampling (CVS): can be performed earlier than an amniocentesis, at 8 to 12 weeks, but carries a greater risk of miscarriage and other pregnancy complications
- Percutaneous Umbilical Blood Sampling (PUBS): also known as fetal blood sampling, this type of testing is performed at 20 weeks and has similar risks as an amniocentesis
Treatment for Down Syndrome
While Down syndrome canï¿½t be prevented or cure, it can be treated. Children with Down syndrome benefit from speech, occupational and physical therapy, which help to improve their motor skills, language and social development.
Depending on the severity of their disease, children can grow up to live full lives, either semi-independently or independently.
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