What is DOWN SYNDROME?
Down syndrome or Down’s syndrome also known as Trisomy 21 is a chromosomal condition that involves extra genetic material (in part or full) on chromosome 21.
Causes of Down syndrome
It occurs once in 800 births and is more common in older parents. The extent of extra material on chromosome 21 may vary depending on genetic history and pure chance. The specific reason for occurrence of Trisomy 21 is still unknown and so is any method to prevent the chromosomal error.
Prenatal Screening and Diagnosis of Down syndrome
Down’s syndrome in a fetus can be detected using a screening test or a diagnostic test. Screening tests estimate the risk that a fetus has Down syndrome and diagnostic tests tell you whether the fetus actually has the syndrome. Screening tests include:
- Nuchal translucency testing
- The triple screen or quadruple screen
- Integrated screen.
- A genetic ultrasound
Diagnostic tests include:
- Chorionic villus sampling (CVS)
- Percutaneous umbilical blood sampling (PUBS).
Medication and Prevention of Down syndrome
Down’s syndrome cannot be prevented and there is no medication available. But symptoms exhibited by the child can be treated individually. Termination of pregnancies diagnosed of Down’s syndrome is also an option and is as high as 92% in some parts of the world.
Risk Factors of Down syndrome
- Congenital heart disease: It found in as much as 50% of cases with endocardial cushion defect being the most prevalent (40%) and ventricular septal defect coming in at a close second (30%).
- Malignancies: Various forms of leukemia are common whereas other forms of cancer are not.
- Thyroid disorders: Hypothyroidism is most common caused by absence of thyroid at birth or due to attack on the thyroid by the immune system.
- Infertility: Infertility is common in both sexes. The female rate of conception is lower and they often have difficulties with labor, with frequent miscarriages and premature births. Only three men having Down syndrome have been recorded as having fathered children.
- Ophthalmology and Otolaryngology
Symptoms of Down syndrome
The symptoms of an individual vary greatly due to differences in genetic mechanisms. Hence predicting symptoms before the birth of the child isn’t possible. Most common symptoms associated with the syndrome are slow mental and physical development and a peculiar set of facial features.
Physical characteristics of Down syndrome may include an unnaturally small chin, weak muscle tone, protruding tongue, a nasal bridge that is flat, short neck, iris with spots or overly lax joints. They may also have a broad face and a round head. Their intellectual disability varies from mild to moderate depending on the type of Trisomy 21. Typically individuals with Trisomy 21 have speech delays and also lag behind in motor skills. They are shorter in stature and at a greater risk of being obese. Their life expectancy is also considerably reduced.
Treatment of Down syndrome
Treatment for children born with Trisomy 21 varies depending on the symptoms exhibited by them. Corrective surgery is recommended for children with heart problems. Plastic surgery is helpful to correct physical characteristics thereby allowing them to lead a normal life to some extent. Cognitive development in children having Down syndrome is varied and can be improved by using augmentative and alternative communication methods. Speech therapy is also an option.
Types of Down syndrome
- Trisomy 21: Occurring in about 95% of people with Down syndrome, it is caused due to an error in cell division before or at the time of conception. In this type a pair of the 21st chromosome does not separate properly in the egg or sperm and this extra chromosome is then found in every cell of the body.
- Mosaicism: The error in separation of the 21st chromosome occurs for a few cell divisions after fertilization due to which some cells have 47 chromosomes and others have 46.The extent of physical issues depends on the ratio of the presence of these two kinds of cells. It occurs in 1-2% of all people with Down syndrome.
- Translocation: In this type, a part of chromosome 21 breaks off and attaches itself to another chromosome (often chromosome 14) and all cells in the body have this extra piece of chromosome 21.It occurs in 3-4% of babies born with Down’s syndrome.
Karyotyping is the test used to identify which type of Down’s syndrome is present in the individual.