Our genes are responsible for all mental and physical traits. So, an additional genetic material that alters the course of development, causing features of “Down syndrome”. To put it in simple terms, the individual will have 47 chromosomes (one extra) instead of 46.
What are the features of Down Syndrome?
You can identify from:
- Facial appearance
- Weak muscle tone
- Variable developmental delays and
- Intellectual disability
- Various anomalies like cardiac, gastrointestinal or endocrine defects with poor immune functions
What causes it?
The extra copy of chromosome 21, also called as Trisomy 21, gets three copies instead of two. This extra copy partial or whole chromosome results in the characteristic of Down syndrome. The genetic material alters the course of development. Due to the maternal age factor, 80% of children with Down syndrome are born to women under 35 years of age. The additional copy of chromosome 21 originates from the mother in 95% of cases and only 5% have been traced to the father.
The risk of Down syndrome increases with age, from 1 to 1000 at 40 years and 1 in 30 at 45 years of maternal age.
What are the different types of Down Syndrome?
There are “three” types of Down syndrome:
- Standard Trisomy 21
But the features are almost same in all varying degrees but milder and fewer in mosaic cases as compared to Trisomy 21.
Dr. Asha Rawal, Senior Consultant, Obstetrics and Gynecology, Max Healthcare Pitampura explains: In standard Trisomy 21, 95% of cases have no egg formation or sperm results in an extra chromosome, non-disjunction. In mosaic Trisomy 21, 2%, not every cell in the body has an extra chromosome or some may be normal with usual two copies. Translocation trisomy, 3%, whole or part of chromosome 21 is present but attached or translocated to a different chromosome and not chromosome 21.
How is Down syndrome diagnosed?
There are two categories of tests for Down syndrome that can be performed before a baby is born.
- Screening - Screening tests like blood tests and ultrasound are easily available to all pregnant women. The blood/serum tests are a Double marker at 11-13.6weeks, Triple and Quadruple marker done at 15 to 20 weeks. These tests are often performed in conjunction with a detailed ultrasonography to check for “markers “of Down syndrome. New advanced prenatal screen is now available which detects chromosomal material of fetal origin from mother’s blood. This test offers high accuracy up to 99.9%.
- Diagnostic tests- The diagnostic tests available are Chorionic villous sampling (CVS) and Amniocentesis. These procedures carry up to 1% risk of miscarriage but are nearly 100% accurate. CVS is carried out at 9-14 weeks and amniocentesis between 16 to 20 weeks of pregnancy.
Down syndrome at birth is diagnosed by identifying the physical traits and confirming by chromosome analysis, called “Karyotype” from the blood sample of the baby.
What impact does Down syndrome have on parents and society?
Children with Down syndrome have cognitive, intellectual delays that may be mild or moderate. There can be structural congenital defects also. Children with this syndrome are accepted by the society and organisation. Due to the medical advancements, children with Down syndrome are living longer than before.
Is there any treatment available?
There is no treatment for Down syndrome. One has to address the congenital, gastrointestinal or heart defects that may require heart surgery. Behavioural training to the child and family can help in dealing with the situation. Women of child bearing age should be well educated and informed about the possible prevention and available tests to diagnose the syndrome early in pregnancy.