Down syndrome or Trisomia 21 is the most common chromosomal condition in U.S, one in every 691 babies in the U.S are born with it (NDSS). More than 400 thousand people live with it in U.S (NDSS).
Risk of giving birth to a baby with the Down syndrome increases with age. If for mothers under 30 Down's Syndrome Risk is less than 1 in 1 000, for mothers aged 35, 42 and 49 the risk increases to 1 in 400, 1 in 60 and 1 in 12 respectively (TheSpecialLife.com).
At the same time, over 80% of children with Down syndrome are born to mothers younger than 35, and the average age of a woman who gave birth to an infant with the syndrome is 28 years.
Down syndrome is not related to nationality, it’s independent of race, and the frequency of this condition doesn’t depend on the family welfare and socioeconomic status.
II. About Chromosomes
Every cell nucleus contain chromosomes made up from DNA, tightly coiled around histones. Short section of DNA is known as gene. Typically human body cells have 46 chromosomes (23 pairs) in the nucleus.
One chromosome from each of the 23 pairs is inherited from each of the parents. The two chromosomes of a pair (except for the sex chromosomes) contain the same genes, but with small differences.
III.About Down Syndrome
The disorder is named after English physician John Langdon Down. There’re three genetic variations that can result in Down’s syndrome.
Trisomy 21 (95% of the cases). People with Down’s syndrome have 47 chromosomes instead of the normal 46. Down syndrome is caused by an error in cell division (nondisjunction) during meiosis. The two copies of chromosome 21 don’t split up during the egg formation. About 90% of the abnormal cells are the eggs (Leshin, 2009). After conception, the baby gets three copies of chromosome 21 in each of the cells.
Robertsonian Translocation (causes 3-4% of all cases). It happens when some of the 14 chromosome is replaced by extra 21 chromosome, 21 chromosome is translocated onto 14 chromosome. Total number of chromosomes is normal, but there’s a triplication of a part or a whole 21th chromosome. Translocation can be inherited in some cases (with risk about 3% if the father is the carrier, 10-15% - if the mother is carrier, according to Mayo Clinic data).
Mosaicism (1-2% of all cases). People have both normal cells and cells with triplicated 21th chromosome. This mixture of cells is observed in various cells of the same type.
IV. Living with Down Syndrome
According to the Global Down Syndrome Foundation, the average life expectancy of an individual with Down’s syndrome in the U.S. is about 60 years.
Down’s syndrome risk is defined during prenatal screening. Presence of the disorder is identified at birth by a set of physical characteristics associated with this condition.
Some people exhibit more features of Down’s syndrome, some only a few. The most common featues of the syndrome are the following:
- Low height, short legs (about 100%);
- Brachycephaly (81%);
- Skinfold on the neck of newborns (81%);
- Low muscle tone (80%), chest deformity. This hypotonia may result in delays in motor development;
- Slanting palpebral fissures, epicant (79%);
- Short and broad hands (64%) with clinodactyly of the fingers;
- Flattened facial features, microgenia, a small nose, abnormally shaped ears;
- Eye issues - brushfield spots – small white spots on the iris (Fay Evans-Martin, 2009), strabismus;
- Various congenital malformations (ventricular septal defect of the heart, duodenal stenosis, etc.)
People with Down’s syndrome are exposed to various complications and deseases. For example, they have increased risk of leukemia, severe infectious deceases such as pneumonia, thyroid diseases, infertility. These people tend to obesity. Also they have increased risk of developing Alzheimer's disease and epilepsy. But there’s some positive outcome of the syndrome – likelihood of many malignant diseases is reduced sufficiently.
About 25% of adults over 35 with Down’s syndrome will show manifestations of Alzheimer's disease.
There is a very wide variation in mental abilities and behavior. Most people with Down’s syndrome “have mild to moderate mental retardation” (Fergus, 2014). Children with the Down syndrome pass through the various stages of development in the same order as other children (Cicchetti, 1990).
All the people with this condition are capable to learning, but they have some streangth and weaknesses in various areas of development.
In childhood, people with Down’s syndrome have some difficulties in abstract thinking, expressive language, grammar and speech clarity. There’s a gap between non-verbal understanding and ability to express their thoughts, that sometimes may result in behavioural disorders. Numeric skills, learning maths is also a weak point. Number skills are usually some “2 years behind their reading skills” (DSE International). Another issue is verbal short-term memory – ability to store and process spoken information is much lower that ability to deal with visual information. Finally, motor skills develop at a slower pace.
Quality of life of people with Down syndrome depends a lot on a stimulating home environment, family and community support, good educational programs and health care treatment. Under these conditions these people can live fulfilling lives developing their full potential.
- National Down Syndrome Society. Down Syndrome Facts. Retrieved from <http://www.ndss.org/Down-Syndrome/Down-Syndrome-Facts/ > Accessed 19 June 2014
- Mayo Clinic. Diseases and conditions: Down Syndrome. Retrieved from < http://www.mayoclinic.org/diseases-conditions/down-syndrome/basics/causes/con-20020948 > Accessed 19 June 2014
- Leshin, L. Trisomy 21: The Story of Down Syndrome. Retrieved from < http://www.ds-health.com/trisomy.htm > Accessed 19 June 2014
- Cicchetti, D., Beeghly M. (1990). Children with Down Syndrome: A Developmental Perspective. Cambridge University Press.
- Prasher, V. P. (2005). Alzheimer's Disease and Dementia in Down Syndrome and Intellectual Disabilities. Abingdon, Oxon, United Kingdom.
- Evans-Martin, F. Fay (2009). Down syndrome. New York, United States.
- Gerbatsch, N. (2014). Down Syndrome – Causes, Symptoms and Opportunities for Development. Germany.
- Selikowitz, M. (2008). Down Syndrome. 8 edition. New York, United States.
- Down Syndrome Facts. The Special Life. Retrieved from < http://www.thespeciallife.com/down-syndrome-facts.html#sthash.43HbZqt3.dpbs >Accessed 19 June 2014
- Fergus, K. (2014). Myths, Misconceptions and Facts about Down Syndrome. Retrieved from < http://downsyndrome.about.com/od/downsyndromesupport/a/mtyhs_ro.htm > Accessed 19 June 2014
- Down Syndrome Education International. Development and learning. Retrieved from < http://www.dseinternational.org/en-gb/about-down-syndrome/development/ > Accessed 19 June 2014.
- Brown, R. (1994). Down syndrome and quality of life: some challenges for future practice. Retrieved from < http://www.down-syndrome.org/reports/26/reports-26.pdf >Acessed 19 June 2014