Extra copies of chromosome 21 lead to a genetic disorder known as Down syndrome where certain symptoms result, such as a degree of cognitive dysfunction and other developmental delays. Common physical characteristics include upward-sloping eyes, a flat bridge of the nose, only one crease in the palm (instead of the usual three), and reduced muscle tone, but not all people with Down syndrome have these characteristics.
In an interview with HT Lifestyle, Dr Sonal Kumta, senior consultant-obstetrician and gynecologist at Fortis Hospital, Mulund explained, “Down syndrome is a condition or genetic abnormality where there is trisomy 21 (three instead of 2 chromosomes). It affects a person’s intellectual development and can lead to congenital abnormalities such as heart defects and poor quality of life.”
She said, “Pregnant women can be tested to see if there is any genetic abnormality in the fetus. They can opt for screening in the first trimester (13 weeks) and Nuchal Translucency (NT), which is an ultrasound-based test and a dual marker test (blood test) that includes pregnancy-associated plasma protein-A (PAPP-A) and The pregnancy hormone is called human chorionic gonadotropin (HCG). These two tests have good reliability so pregnant women should have these tests to pick up common genetic problems. Post the results, it is important to see your gynecologist for further evaluation.”
Dr Shiv Murarka, Senior Scientist-Reproductive Genomics, Newburgh Center for Genomic Medicine said, “Pregnant mothers are offered routine prenatal tests for various reasons and at different stages of pregnancy. They include blood tests (including biochemical marker screening) and ultrasound tests that can predict the likelihood that your baby will be born with several diseases, such as Down syndrome.”
Talking about prenatal testing options, he said, “The chances of having a baby with Down syndrome can be detected through screening tests. Although screening carries no risk of miscarriage, the test can suggest the possibility of whether the fetus is affected. In contrast, diagnostic tests have a low risk of miscarriage (often less than 1%), but they are accurate in detecting various fetal abnormalities. The American College of Obstetricians and Gynecologists (ACMG) recommends that all pregnant women, regardless of age, be offered screening tests for Down syndrome and a choice of diagnostic tests.
Dr Shiva Murarka suggested:
A. Screening Tests
It is non-invasive in nature and the test is done from the mother’s blood
Non-invasive prenatal testing (NIPS)
· Initial performance as early as 9 weeks of pregnancy and results are available within 7 days.
B. Diagnostic Tests
It is invasive in nature and is performed on amniotic fluid (AF) or chorionic villus sampling (CVS).
An amniocentesis procedure for genetic testing is usually done at 16-20 weeks while CVS at 11-13 weeks of pregnancy.
1. Traditionally chromosomal karyotyping and fluorescent in situ hybridization (FISH).
· Karyotyping usually takes 15-20 days for reporting as it involves the process of culturing the cells.
· FISH is the gold standard for detecting five common aneuploidies. It is the only technique that detects low-level mosaicism.
2. Microarray
· It is a very high resolution molecular cytogenetic technique. Recently, Neuberg launched the Cyto-one test which is an upgraded version of existing microarray tests. Microarrays can detect microdeletions/microduplications providing better coverage of fetal disorders.
3. PAN – Antenatal Aneuploidy Test
The PAN test is able to detect abnormalities in all chromosomes and sub-chromosomal regions, the advantage being that it has better sensitivity and detection than the current test. It can detect more disorders and covers all chromosomes instead of just 5, which expands its scope and coverage. The test has a quick turnaround time of 48-72 hours and costs the same as previous tests, making it more accessible to doctors and patients.
Dr. Shiva Murarka concluded, “If a screening test yields a positive result, we advise you to talk to your doctor and geneticist about the results and options. What types of diagnostic tests are available to confirm a positive result will be explained. Furthermore, if diagnostic testing reveals a genetic anomaly, the implications of these findings should be discussed with specialists in the condition, including a medical geneticist and your doctor.