Down syndrome is a chromosomal disorder caused by an error in cell division that results in the presence of an additional third chromosome 21 or Trisomy 21. The genesis of the name Down syndrome came from an English physician, Dr. Langdon Down who made the first distinction between children who were cretins and what he referred to as Mongoloid because he thought they looked like the people from Mongolia. The name was rejected by Asian genetic researchers in the early 1960s and it was dropped from scientific use. The condition became to be known as Down’s syndrome which the Americans revised to be Down syndrome.
It wasn’t until 1959 that Jerome Lejeune and Patricia Jacobs, working independently first determined the cause to be Trisomy or triplication of the 21st chromosome. Down syndrome affects approximately 1 in 800 to 1000 live births in all races and economic groups. There are more than 350,000 individuals with Down syndrome in the US according to the National Down Syndrome Society. Causes Human body is made up of cells, half of the cell’s components being inherited from each parent. The sperm cell has 23 chromosomes and the ovum cell has 23 chromosomes.
When combined during fertilization, the fertilized egg that results has 23 chromosome pairs. A female develops with chromosome pair from 1 to 22 and a pair XX while a male has 1 to 22 and a XY pair. There can be an error during the cell division and the resulting cell has 24 chromosomes of which the extra one is chromosome 21. If the fertilized egg contains an extra chromosome 21, then it results in Down syndrome. There are three variations that cause Down syndrome: • The presence of an extra chromosome 21 in all cells of an individual. This accounts for 92% of all the cases.
The extra chromosome originates in the development of either the egg or the sperm and instead of the fertilized egg having two chromosome 21 it has three which is repeated in every cell. This is referred to as Trisomy 21. • There is mosaic Trisomy 21 and this accounts for 2% – 4% of all the cases. This is similar to Trisomy 21 only that the extra chromosome 21 is present in some but not all the cells of the individual. The fertilized egg may have the right number of chromosomes but an error may occur in the early embryonic development which results in some cells acquiring an extra chromosome 21.
In this type the physical problems vary depending on the proportion of cells that carry the extra chromosome 21. • There is translocation Down syndrome which accounts for 3% – 4% of individuals with Down syndrome. In this case, individuals have 46 chromosomes in their cells but materials from one chromosome 21 gets stuck or translocated onto another chromosome, mostly chromosome 14, either prior to or at conception. In such a situation, cells from the individual have two normal chromosome 21 but also have additional materials on the translocated chromosome and this results in the features associated with Down syndrome.
Most genetic disorder includes of birth defects, including some degree of mental retardation, characteristics facial features and often heart defects, visual and hearing impairment and other health problems. Physical signs Children with Down syndrome have upward slanted eyes and small ears that may fold slightly at the top. They have small mouths which make their tongue seem bigger. Their nose may be small with a flattened nasal bridge . Other have a short necks and small hands with short fingers.
Rather than having 3 creases in the palm of the hand, they have one crease that goes straight across the palm and a second crease that curves down by the thumb. They are a bit short and have looseness of the joints. A child with Down syndrome will have some of the features but not all. Health problems There are different health problems associated with Down syndrome. These vary from child to child. • About 40-50% of babies born with Down syndrome have heart defects. Some are minor and can be medicated while others require surgery. • About 10% have intestinal malfunctions that require surgery
• They are usually at increased risk for visual or hearing impairment which may include crossed eyes, near or far sightedness and cataracts. These can be improved with glasses surgery or other treatments. • They may develop hearing loss due to fluid in the middle ear, a nerve defect or both and therefore should have regular hearing examinations. • They are at increased risk of thyroid problems and leukemia and may tend to have colds, bronchitis and pneumonia. They should have regular medical care including childhood immunizations The occurrence of Down syndrome is random and can not be attributed to any behavioral or environmental factors.
The probability of having another child with Down syndrome in subsequent pregnancy is about 1% regardless of maternal age. The incidence though rises with increasing maternal age. The risk for bearing a child with Down syndrome for 25 to 29 years mothers is 1 out of 250 while for age 45 and above is 1out of 30 births. Diagnosis Down syndrome can either be tested before birth or after birth. There are three tests which can be done in prenatal screening. • Amniocentesis-This involves the removal and analysis of small samples of fetal cells from the amniotic fluid. It can only be done after the 14th-18th week of the pregnancy.
• Chorionic villus sampling-This involves the extraction of tiny amounts of fetal tissues at 9 to 11 weeks of pregnancy which are tested for the presence of chromosome 21. • Percutaneous umbilical blood sampling (PUBS)-This is the extraction of tissue from the umbilical cord which are then tested for the presence of extra material from chromosome 21. This can not be done till the 18th- 22nd week of pregnancy. These tests however carry a considerable risk of miscarriage with the latter having the highest probability. After birth the doctor may recognize the physical features associated with Down syndrome.
To confirm the diagnosis a blood test known as chromosomal karyotype is carried out to determine if extra material from chromosome 21 is present. Their life expectancy is about 55 years though the average lifespan varies. According to Paul, Mary and Sue (1992), the probability of survival in young children is affected by the presence of congenital cardiac disease. These individuals need appropriate medical care designed to enhance the quality of their lives. Early interventions like physical and speech therapy will help the children develop their motor and communication skills faster.
They also need maximum opportunity to maintain their cognitive gains of early childhood and their health and strength as adults. Treatment There is no cure yet for Down syndrome but researchers are working on it. However there are treatments and therapies for physical, medical and cognitive problems associated with Down syndrome. A variety of approaches can be used to treat these conditions: Medications for minor defects, surgical treatments for example for congenital heart defects, early interventions for physical therapies which focus on motor development and speech therapy which help them learn to communicate clearly. Prevention
In his report Cuckle (2005) considers three potential prevention strategies which have however not been medically proven: Avoiding reproduction at advanced maternal age as it may substantially reduce the risk, pre-implantation genetic diagnosis for couples who are at high risk of Down syndrome and folic acid supplementation. There is however no concrete scientific evidence that show the above measures can prevent Down syndrome. Down syndrome is a genetic disease and although no cure or prevention measures have been found, individuals with Down syndrome can live a full life with early interventions and proper medical care.
Although they may develop a little slower than their peers, with time they gain the necessary life skills and also develops cognitively although their IQ is lower than a regular person’s. Each individual with Down syndrome has unique needs and so proper individualized medical care and early intervention should be given. References Coleman, M. , Rogers, P. t. , Buckley, S. , (1992) Medical Care in Down Syndrome: A Preventative Medicine Approach.
Marcel Dekker, Inc, NY. Cuckle, H. S. , (2005; 2:93-99), International Journal of Medical Science, Primary prevention of Down’s syndrome, Viewed on 14, March 2009, <http://www. medsci. org/v02p0093. htm> Leshin, L., (2003), Trisomy 21: The Story of Down Syndrome, Viewed on 15, March 2009, <http://www. ds-health. com/trisomy. htm>. MedicineNetInc (2009), Down syndrome, Viewed on 14, March 2009, < http://www. medicinenet. com/down_syndrome/article. htm> University of Virginia Health Systems (2008), Medical Genetics: Down Syndrome (Trisomy 21, Viewed on 14, March 2009, <http://www. healthsystem. virginia. edu/uvahealth/peds_genetics/downs. cfm>