Trisomy 21 or Down syndrome is a genetic defect in which there are three chromosome 21s instead of two. This may be caused due to abnormal cell division. This condition is characterized by birth defects, intellectual problems and distinct facial features.
Every year around 23,000 -29,000 children are born with trisomy21 in India, which is highest in the world. Women who conceive after 30years of age are at high risk of having a baby with Down syndrome. Moreover, couples who have already had one child with Down syndrome or have a family history of having babies with Down syndrome are at a slightly increased risk of having a second child with Down syndrome. If a parent carries the defective gene responsible for Down syndrome, it is highly likely that their baby has Down syndrome.
Symptoms
Facial features: Small head, flat face with eyes slanted upwards, depressed nasal bridge, white spots in the eye, small ears, protruding tongue, short and wide neck.
Broad, short hands and feet
Short height
Constipation
Heart defects
Celiac disease
Hypothyroidism
Dental problems
Poor muscle tone
Hearing problems
Cognitive disability
Excessive flexibility
Susceptibility to respiratory infections
Depression associated with autism or Attention deficit hyperactivity disorder
Diagnosis
Maternal screening Tests:
Screening tests indicate whether the baby is at risk of having Down syndrome. If screening is positive, then diagnostic tests are done to confirm the presence of Down syndrome. Screening test for Down syndrome includes
First trimester screening:
It includes blood test and nuchal translucency test. This test is ideally done between 11 and 12 weeks of pregnancy.
Blood test: Human chorionic gonadotropin(HCG) the pregnancy hormone plasma protein A (PAPP-A) is a protein produced by the placenta. The levels of these components are altered in fetus with Down syndrome. The test that measures the levels of HCG and PAPP is also referred to as double marker test.
Nuchal translucency test: It is a special ultrasound scan in which the fluid collection under the neck of the fetus is measured. In a fetus with Down syndrome, this collection of fluid is normal.
Combined results of these two tests would indicate the risk of Down syndrome in the fetus.
Second trimester Screening:
Maternal marker tests are a series of tests done in the second trimester to evaluate a woman’s risk of carrying a baby with chromosomal anomalies. It includes- double marker test, triple marker tests and quadruple marker test. These tests are done usually between 15-20 weeks of pregnancy.
The triple marker test assesses the levels of alphafetoprotein, a protein produced by the fetus, hCG and estriol which are the hormones produced by the placenta. This test helps in detecting genetic defects such as Down’s syndrome and neural tube defect such as spina bifida. This test also detects multiple pregnancy.
The quadruple marker test assesses the levels of alphafetoprotein, hCG, estriol and Inhibin A, which is a protein produced by the placenta and ovaries. The chances of identifying pregnancies with Down syndrome is considerably more with this test.
Diagnostic tests
If screening test results are positive, then the following diagnostic tests are done to confirm that the fetus has Down syndrome.
Chorionic villus sampling: It is done during first trimester between 10 to 13 weeks of pregnancy. In this test, a small sample of tissue from chorionic villi(a part of the placenta) is taken. The genetic material in the cells of this chorionic villi is the same as that of the developing fetus. Genetic testing of this sample is done to find out if the fetus has Down syndrome. This procedure has a low risk of miscarriage.
Amniocentesis: It is done during second trimester after 15 weeks of pregnancy. Amniotic fluid contains cells of the baby which are shed during development. In this procedure, a sample of the amniotic fluid is taken and is tested for abnormality in the chromosomes in the cells of the fetus. This procedure also has low risk of miscarriage.
Percutaneous Umbilical Cord Blood Sampling: It is done during second trimester after 17 weeks of pregnancy. Fetal blood is retrieved from the umbilical cord and a chromosomal analysis is done.
Diagnostic tests after pregnancy: Down syndrome can be detected at birth based on the facial and bodily features of the baby, However, a chromosomal analysis of the baby blood is done to confirm Down syndrome.
Treatment
There is no cure for trisomy 21. The quality of life in children with Down syndrome can be improved with the use of proper medical interventions. Therapies such as physical therapy ( for improving motor skills, posture and balance), speech-language therapy (for improving communication skills), occupational therapy (for improving ability to perform daily tasks) and emotional and behavioral therapy (for improving control over emotions) are useful to live with Down syndrome. Assistive devices such as amplification devices for hearing problem, touch screen computers are also used.Counselling and joining support groups would help the parents to cope with the challenges for raising a child with Down syndrome.
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References
http://www.stanfordchildrens.org/en/topic/default?id=down-syndrome-trisomy-21-90-P02356. Down syndrome (Trisomy 21). Accessed on 25-Oct-2017.
https://www.livescience.com/27248-chromosomes.html. Chromosomes: Definition & Structure. Accessed on 25-Oct-2017.
https://www.omicsonline.org/india/down-syndrome-peer-reviewed-pdf-ppt-articles/. Down Syndrome. Accessed on 25-Oct-2017.
http://americanpregnancy.org/birth-defects/down-syndrome/. Down Syndrome: Trisomy 21. Accessed on 25-Oct-2017.
https://www.mayoclinic.org/tests-procedures/first-trimester-screening/basics/why-its-done/prc-20014597. First trimester screening. Accessed on 25-Oct-2017.
https://www.babycenter.com/0_chorionic-villus-sampling-cvs_328.bc. Chorionic villus sampling (CVS). Accessed on 25-Oct-2017.
https://www.nichd.nih.gov/health/topics/down/conditioninfo/Pages/treatments.aspx. What are common treatments for Down syndrome?. Accessed on 25-Oct-2017.
