Extra copies of chromosome 21 lead to the genetic disorder known as Down Syndrome where some traits are the outcome, such as a degree of cognitive dysfunction and other developmental delays. Typical physical characteristics include eyes that slant upward, a flattened bridge of the nose, just one crease on the palm (instead of the customary three), and diminished muscular tone but not every person with Down syndrome possesses all of these characteristics.
In an interview with HT Lifestyle, Dr Sonal Kumta, Senior Consultant-Obstetrician and Gynecologist at Fortis Hospital in Mulund, explained, “Down Syndrome is a condition or genetic abnormality where there is trisomy 21 (instead of 2 chromosomes there are three). This impacts an individual’s intellectual development and can cause congenital abnormalities like heart defects and poor quality of life.”
She elaborated, “A pregnant woman can undergo tests to check if the fetus has any genetic abnormalities. They can opt for screening in the first trimester (13 weeks) and undergo Nuchal Translucency (NT), which is an ultrasound based test and dual marker test (blood test) which includes Pregnancy-Associated Plasma Protein-A (PAPP-A) and the pregnancy hormone known as Human Chorionic Gonadotropin (HCG). These two tests have good reliability so pregnant women should do these tests to pick up common genetic problems. Post the results, it is important to meet your gynecologist for further evaluation.”
Dr Shiva Murarka, Senior Scientist-Reproductive Genomics, Neuberg Centre for Genomic Medicine, said, “Routine prenatal tests are provided to expectant mothers for a variety of reasons and at various stages of the pregnancy. They comprise screening examinations including blood tests (including Biochemical Markers screening) and ultrasound examination that can predict the likelihood that your child will be born with a number of diseases, such as Down syndrome.”
Talking about prenatal testing options, he said, “An increased chance of having a child with Down syndrome can be found by screening tests. Although getting screened carries no risk of miscarriage, the test can suggest the likelihood whether the fetus is impacted. Contrarily, diagnostic tests have a low risk of miscarriage (often less than 1%), but they are accurate at detecting various fetus abnormalities. The American College of Obstetricians and Gynecologists (ACMG) recommends offering the option of screening tests and diagnostic tests for Down syndrome to all pregnant women, regardless of age.”
Dr Shiva Murarka suggested:
A. Screening Tests
This is non-invasive in nature and the test is performed from the mothers blood
Non-invasive Prenatal Tests (NIPS)
· Performed as early as 9 weeks of pregnancy and results are available within 7 days.
B. Diagnostic Tests
This is invasive in nature and is being performed on amniotic fluid (AF) or chorionic villus sample (CVS).
An amniocentesis procedure for genetic testing is typically performed at 16-20 weeks while CVS at 11-13 weeks of pregnancy.
1. Conventionally chromosomal Karyotyping and fluorescent in situ hybridization (FISH).
· Karyotyping usually takes 15-20 days for the reporting as it involves the process of culture of cells.
· FISH is gold standard for the detection of five common aneuploidy detection. This is the only technique to detect low-level mosaicism.
· This is molecular cytogenetic technique with a very high resolution. Recently, Neuberg launched Cyto-one test which is an upgraded version of existing microarray tests. Microarray can detect microdeletions/microduplications that provide better coverage of fetal disorders.
3. PAN – Prenatal Aneuploidy Test
· The Pan test is capable of detecting abnormalities on all chromosomes and sub-chromosomal regions, The advantage is that it has better sensitivity and detection capabilities 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 the previous tests, making it more accessible to doctors and patients.
Dr Shiva Murarka concluded, “We advise that you speak with your doctor and a geneticist about the consequences and your alternatives if a screening test yields positive results. What kinds of diagnostic tests are available will be explained to confirm the positive outcome. Furthermore, the implications of the these finding should be discussed with the condition’s experts, including a medical geneticist as well as your doctor, if a diagnostic test reveals a genetic anomaly.”