Trisomy 21 (Down Syndrome)
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Description
Trisomy 21 (T21), or Down syndrome, is one of the most common genetic disorders caused by an extra copy of chromosome 21. Chromosomes are the genetic material that determine the growth and functions of human beings. Usually, humans have 2 copies of each chromosome. Humans with Trisomy 21 have 3 copies of chromosome 21. T21 causes certain physical characteristics, developmental delays, and learning disabilities. T21 can cause heart, vision, and hearing problems. T21 occurs in 1 in 700 live births and is not an inherited disorder in most cases.
Screening and Diagnosis
Down syndrome can be diagnosed before or after birth. If testing before birth, amniocentesis or chorionic villus sampling (CVS) testing can diagnose Down syndrome. A positive prenatal biochemical screen (e.g., Quad test) or NIPT/NIPS screen indicates the chance of a higher risk for this abnormality. NIPS screens for T21 are more accurate among women at high risk (e.g,, over the age of 35), but when women at low-risk (less than 35 years of age) are screened, NIPT/NIPS can be wrong 50% of the time or more. Therefore, follow-up confirmatory diagnostic testing is recommended to confirm any positive T21 screening result (a diagnostic test such as amniocentesis, CVS, or newborn screening). Amniocentesis tests the amniotic fluid during the second or third trimester of pregnancy and CVS tests the placenta to confirm a T21 diagnosis. These diagnostic tests pose a 1 in 500 risk of miscarriage.
Treatment/Prognosis
Treatments for Trisomy 21, or Down Syndrome (DS), address secondary conditions a child may experience such as congenital heart defects, physical anomalies, seizures, and hypothyroidism. Treatment can include surgery, physical therapy, speech therapy, and behavioral therapy. T21 is usually not fatal and, with appropriate medical care, people with Down syndrome can live happy lives with an average life expectancy of 60 years. A study reporting on families of children with T21 has found that “an overwhelming majority of parents love their son or daughter with DS and are proud of them” and “felt their outlook on life was more positive because of them” (See Skotko et al, 2011 below).
Medical advances are continually improving treatment options and outcomes so consulting with specialists and major children’s hospitals may be beneficial to find the best possible care.
Sources:
https://www.massgeneral.org/children/down-syndrome/trisomy-21-down-syndrome
https://www.mayoclinic.org/diseases-conditions/down-syndrome/symptoms-causes/syc-20355977
https://www.stanfordchildrens.org/en/topic/default?id=down-syndrome-trisomy-21-90-P02356
Down Syndrome | Diagnosis & Treatments | Boston Children's Hospital (childrenshospital.org)
Trisomy 21 (Down Syndrome) | Children's Hospital of Philadelphia (chop.edu)
Down Syndrome - Dive Deeper - Voyage of Life
Facts about Down Syndrome - National Association for Down Syndrome
Skotko, B. G., Levine, S. P., Macklin, E. A., & Goldstein, R. D. (2016). Family perspectives about Down syndrome. American journal of medical genetics. Part A, 170A(4), 930–941. https://doi.org/10.1002/ajmg.a.37520
Skotko, B. G., Levine, S. P., & Goldstein, R. (2011). Having a son or daughter with Down syndrome: perspectives from mothers and fathers. American journal of medical genetics. Part A, 155A(10), 2335–2347. https://doi.org/10.1002/ajmg.a.34293