(DS; Trisomy 21)
Down Syndrome – Definition
Down syndrome is a common genetic disorder. It occurs in one out of 700-800 live births. Down syndrome causes birth defects, medical problems, and some degree of intellectual disability.
In fact, down syndrome is the most common genetic cause of mild to moderate intellectual disabilities.
Down Syndrome – Causes
Chromosomes contain the genetic makeup of your body. They occur in 23 pairs within the body. Down syndrome is a problem with chromosome pair 21. There is extra genetic material on this chromosome which may be caused by:
- An extra chromosome — this type is called Trisomy 21. This results from an error in cell division in the egg or sperm.
- Extra chromosomes in some cells — called Mosaic Trisomy 21.
- Part of the chromosome has broken off and reattached to another chromosome—called translocation trisomy. In about one third of individuals, the translocation is inherited from a parent.
Down Syndrome – Risk Factors
Factors that increase the chance for Down syndrome include:
- Genetics: If either parent is a carrier of Translocation Down syndrome, there is an increased risk.
- Age: The chance of having a child with Down syndrome increases after a woman reaches age 35.
- Sex: More boys than girls are born with Down syndrome.
- History of a previous child with Down syndrome.
Down Syndrome – Symptoms
Infants born with Down syndrome may have some or all of the following physical features:
- Muscle hypotonia, low muscle tone
- Flat facial features, a somewhat depressed nasal bridge and a small nose
- Upward slanted eyes, small skin folds on the inner corner of the eyes
- Short neck
- Misshaped ears
- White spots on the colored part of the eye
- Single skin crease in the palm of the hand
- Excess flexibility in joints
- Heart defects
- Sight and hearing problems
- Large and protruding tongue
- Fifth finger has one flexion furrow instead of two
- Excessive space between large and second toe
The degree of medical problems and intellectual disability is different for each person. Talents, abilities, and pace of development will be different too. People with Down syndrome may be born with or develop:
- Vision problems
- Hearing loss
- Heart defects
- Increased incidence of acute leukemia
- Frequent ear infections and increased susceptibility to infection in general
- Gastrointestinal obstruction (imperforate anus and similar problems)
- Esophageal atresia or duodenal atresia
- Sleep problems (eg, blocked airways during sleep, daytime sleepiness, sleep anxiety, sleep walking)
- Increased incidence of dementia in older ages
- Instability of the back bones at the top of the neck, can result in compression injury of the spinal cord
- Urinary system defects
- High blood pressure in the lungs
- An under-active thyroid ( hypothyroidism)
- Slow growth
- Late to sit, walk, toilet train
- Speech problems
- Emotional problems
Most of these health problems are treatable. The majority of people born with Down syndrome today have a life expectancy of about 55 years.
Down Syndrome – Diagnosis
Doctors can usually identify a child born with Down syndrome at birth. When Down syndrome is suspected, a blood test will be done to confirm it.
Down syndrome may also be diagnosed before birth. It may happen during a screening test or a diagnostic test.
A screening test is done to estimate the risk of having a child with Down syndrome. Your doctor will use the results of a variety of blood tests and the mother’s age to estimate the risk. Blood tests may include:
- Triple screen
- Quadruple screen
- Massively parallel sequencing (MPS)
- Alpha-fetoprotein Plus
Screening may be done as early as 11 weeks. It may also include both ultrasound imaging and blood screening. There should be a follow-up in the second trimester for those who screen negative.
A small amount of women who have screening will be given false-positive readings. This means the test indicates Down syndrome even when it does not exist.
Diagnostic tests will tell whether or not the fetus actually has Down syndrome. These tests include:
- Chorionic villus sampling (CVS) — usually done between 10 and 12 weeks
- Amniocentesis — usually done between 12 and 20 weeks of gestation
- Percutaneous umbilical blood sampling (PUBS) — usually done after 20 weeks
These tests are about 98%-99% accurate. Each test requires that a small piece of tissue is removed from the placenta or umbilical cord. This creates a small risk of miscarriage with these tests.
Down Syndrome – Treatment
There is no cure for Down syndrome.
Treatment may be needed for severe problems or to help with developmental delays. Living at home and receiving special therapy helps children with Down syndrome achieve their full potential. Most people with the condition can actively participate in the community. This includes activities at schools, jobs, and various leisure activities. Some people with Down syndrome live with family, some with friends, and some live independently.
Some newborns may need surgery to repair serious medical problems, like heart defects.
Infants with Down syndrome may take longer to feed. A child with Down syndrome will also start talking, playing, and performing other activities later than normal.
Learning opportunities may be increased with:
- School programs designed to meet the child’s special needs.
- Mainstreaming children into regular public school classes (with additional support as needed)—in children who have accomplished academic milestones
Speech, physical, and occupational therapy may improve abilities. Therapy can help with speech, walking, and performing activities of daily living.
Professional support helps a family cope with caring for a child with birth defects and intellectual disability. Mental health professionals offer help with managing emotional problems.
Down Syndrome – Prevention
There are no guidelines for preventing Down syndrome. If you have concerns about having a child with Down syndrome, consider getting genetic counseling before becoming pregnant.