Down syndrome and Genetics

A genetic disorder called Down syndrome (DS) is connected to chromosomal abnormalities. Intellectual impairments, distinctive facial features, and hypotonia are all signs of down syndrome (weak muscle tone in infancy). Cognitive development is delayed in those with Down syndrome. But mild to moderate intellectual impairments are common (Antonarakis, Lyle, and Dermitzakis).
Many congenital impairments may be present in people with Down syndrome. For instance, inborn cardiac abnormalities are seen in about 50% of the affected newborns. Additionally, although they are less common, digestive problems such intestinal obstructions have been recorded. The people with Down syndrome (DS) fall at high risks of developing many health complications. For instance, gastroesophageal reflux; a retreating flow of the acidic stomach contents back to the esophagus. Down syndrome individuals also develop celiac disease; an intolerance of the grain (wheat) protein known as gluten (Cohen). Close to 15% of the Down syndrome patients have underactive thyroid gland; a condition referred to as hypothyroidism. Moreover, the Down syndrome patients have increased risks of developing eye and ear problems. Furthermore, a small percentage of Down syndrome (DS) suffering children have a risk of developing leukemia (cancer of the blood-forming cells) (U.S. National Library of Medicine).

The children with Down syndrome exhibit behavioral, and delays in development. The speech and language development are delayed and slower in the Down syndrome children than in those born without the condition (Carter, Capone, and Gray). The affected speeches of the affected children are hard to comprehend. The behavioral problems include; attention problems, compulsive/obsessive behavior, tantrums or stubbornness (Chapman RS). A few people who have Down syndrome (DS) have also been diagnosed with ASD (Autism Spectrum Disorder); a developmental complication that affects an individual’s social interaction, and communication (Carter, Capone, and Gray).

According to (Korenberg) the most evident neurological symptom of Down syndrome is the Alzheimer disease. Alzheimer disease is present in about 100% of the Down syndrome individuals especially when they reach 35 years. By the age of 40 years, about 30% of the individuals will exhibit Alzheimer disease-like dementia (Kesslak, Nagata, and Lott).

Genetics of the condition

As mentioned earlier, Down syndrome (DS) is a chromosomal defect; caused by an additional chromosome in the cells. The chromosomes are the basic structural materials that comprise of the genetic information required for the growth and development of humans. Moreover, the chromosomes are found in all cells within the body.

A typical chromosome constitutes of the deoxyribonucleic acid (DNA); the compound that contains the encoded genetic information (gene), that is relevant for the development of the body structures, as well as the functioning of the body. Each chromosome is made up of thousands of genes; that control the development of the human body. Suppose one has little or too much of the chromosomes, the development is significantly affected.

Every cell in a human body is made up of 46 chromosomes that occur in 23 pairs. The 23 chromosome pairs are labeled from 1 to 23 such that the 23rd pair (sex-chromosomes) is the last. The sex-chromosomes are responsible for determining whether a baby if male or female. In people with DS, an additional copy of the 21st chromosome exists (Victoria).

There are mainly three types of Down syndrome (DS) conditions depending on the chromosomal interactions;

1. Trisomy 21

Trisomy 21 comprises 95% of the Down syndrome individuals. In Trisomy 21 Down syndrome, each cell has an additional copy of chromosome 21; it is the most common type of Down syndrome. Because of the extra chromosome 21, the people with Trisomy 21 have 47 pairs of chromosomes in every cell rather than the standard 46 pairs. Unusual cell division causes the regular trisomy 21 during the formation of an ovum or sperm. The unusual cell division leads to an egg cell or a sperm cell that contains 24 chromosomes instead of the usual 23 chromosomes. When the abnormal gamete (sperm or egg cell) containing 24 chromosomes meets a normal gamete with 23 chromosomes, an abnormal fetus with 47 chromosomes instead of 46 is formed. Up to now, there is no sufficient knowledge of why the abnormal cell division occurs. Therefore, there is no possibility of predicting that abnormal gametes may be formed (Kessling and Sawtell).

2. Mosaic Down syndrome

Mosaic Down syndrome affects 1-2% of the persons suffering from DS. In Mosaic Down syndrome only a few but not all cells have an additional copy of the 21st Chromosome. The rest of the body cells are normal (contain the typical composition of genetic material). Mosaic Down syndrome (DS) leads to lower levels of intellectual disabilities, as well as less obvious facial appearances (Victoria).

3. Translocation Down syndrome

Translocation Down syndrome affects between 3-4% of the persons with Down syndrome. In Translocation Down syndrome, an extra copy of the 21st chromosome is either translocated or attached to a different chromosome. However, the variation doesn’t change the effect of the DS. The translocation DS may be hereditary; transferable from the parents to the children (Victoria).

Diagnosis of Down syndrome

The identification of the type and presence of Down syndrome confirmed by blood tests. The blood tests for Down syndrome are done immediately after birth. Moreover, ultrasound screening during 1st and 2nd trimester is used. The screening helps the doctors to assess the development of the fetus and know if the baby has Down syndrome or not. However, the ultrasound and the blood tests are usually not convenient and give false results. The diagnostic tests like amniocentesis or chorionic villus sampling give more reliable results concerning Down syndrome in babies.

Factors that increase risk of Down syndrome

The risk of giving birth to a baby with DS is directly proportional to the mother’s age. However, mothers of any age can give birth to babies with the DS defect. Many medical experts believe that the risk is higher for mothers aged 35 years and above. If one has a brother or sister with Down syndrome, she has a high risk of giving birth to a Down syndrome-affected the baby. Moreover, a mother who has ever given birth to a baby with DS has a high risk of giving birth to another child with the same condition.

Treatment of Down syndrome

So far, there is no specific cure for Down syndrome; the doctors and parents are encouraged to manage the characteristic features of the disease. For instance, the hypothyroidism effect is managed by administering thyroid hormone. The application of thyroid hormone to hypothyroidism affected Down syndrome children helps in preventing deterioration of intellectual disability. Moreover, the thyroid hormone assists in the improvement of one’s entire functions such as communication, and academic achievements. The cardiac management is done by giving diuretics and digitalis; these treatments assist in preventing heart problems associated with Down syndrome. The psychiatric disorders need to be addressed by giving behavioral and psychological therapy. It is also necessary to give immunization and vaccination for influenza and pneumonia in case the Down syndrome children have chronic respiratory or cardiac complications. Other types of management include the screening for celiac disease which has symptoms such as diarrhea, constipation, weight loss, and bloating as well as stunted growth. Gluten-free diets assist in the treatment of celiac disease. In case if obesity is present, the patient needs to be put under dietary control and increased physical and social activities. If the Down syndrome individual has leukemia, a bone marrow transplant may assist in the generation of blood cells (Mundakel).

Conclusion

Down syndrome (DS) is a genetic disorder caused by abnormalities in the chromosomes. The most common cause of Down syndrome (trisomy 21) is caused by the formation of an extra pair of the 21st chromosome during gametogenesis. The extra chromosome 21 leads to the creation of the sperm or egg cell with 24 chromosomes rather than 23 chromosomes. Eventually, a fetus/ baby with 47 chromosomes rather than the normal 46 chromosomes is formed. It is not yet known why the abnormal gamete formation occurs. Down syndrome is diagnosed using ultrasound screening as well as blood tests. The chorionic and amniotic sampling is also done in the diagnoses of Down syndrome. The Down syndrome individuals have characteristic facial appearances as well as cognitive developmental and behavioral features. The Down syndrome people have a high risk of developing cardiac complications, hypothyroidism, leukemia as well as celiac disease. So far, the treatment of Down syndrome is not sufficiently known. The doctors and parents embark on the management of the characteristics of the conditions.



Works Cited

Antonarakis, SE, et al. "Chromosome 21 and down syndrome: from genomics to pathophysiology." Nat Rev Genet 5.10 (2004): 725-738. Print.

Carter, JC, et al. "Autistic-spectrum disorders in Down syndrome: further delineation and distinction from other behavioral abnormalities." Am J Med Genet B Neuropsychiatr Genet (2007): 97-94. Print.

Chapman RS, Hesketh LJ. "Behavioral phenotype of individuals with Down syndrome." Ment Retard Dev Disabil Res Rev 6.2 (2006): 84-95. Print.

Cohen, WI. "Current dilemmas in Down syndrome clinical care: celiac disease, thyroid disorders, and atlanto-axial instability." Am J Med Genet C Semin Med Genet (2006): 141-148. Print.

Kesslak, J.P., et al. "Magnetic resonance imaging analysis of age related changes in the brains of individuals with Down's syndrome." Neurology 44 (1994): 1039-105. Print.

Kessling, Anna and Mary Sawtell. The Genetics of Down's Syndrome. 2017. Web. 13 December 2017. .

Korenberg, J.R. "Mental modelling." Nature Genet 11 (1995): 109-111. Print.

Mundakel, Gratias Tom. Down Syndrome Treatment & Management. 17 Jan 2017. Web. 13 Dec 2017. .

U.S. National Library of Medicine. Down syndrome. 2017. Web. 13 December 2017. .

Victoria. The genetics of Down syndrome. 2017. Web. 13 December 2017. .