4 Risk Factors Linked to Down Syndrome

Down syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of an extra copy of chromosome 21. It is one of the most common chromosomal abnormalities, affecting approximately 1 in 700 live births. While the exact cause of the extra chromosome remains unknown, certain factors can increase the likelihood of a baby being born with Down syndrome.

One of the most significant risk factors for Down syndrome is maternal age, particularly for women over 35. The risk increases because older eggs have a higher chance of undergoing abnormal chromosomal division during meiosis.

How Maternal Age Affects Risk:

• Women in their 20s: Risk is approximately 1 in 1,500.

• Women at 35 years old: Risk increases to 1 in 350.

• Women at 40 years old: Risk rises to 1 in 100.

• Women at 45 years old: Risk can be as high as 1 in 30.

Although older mothers have a higher individual risk, most babies with Down syndrome are born to younger mothers because more births occur in younger age groups.

While most cases of Down syndrome result from a random extra chromosome 21, some cases (about 3–4%) occur due to a genetic translocation. In these cases, a part of chromosome 21 attaches (translocates) to another chromosome before or during conception.

Key Points About Translocation:

• It can occur spontaneously or be inherited from a parent.

• A parent who is a balanced translocation carrier does not have Down syndrome but has an increased risk of passing the condition to their child.

• Genetic testing can help determine if a parent carries a translocation.

Parents who have had one child with Down syndrome are at an increased risk of having another baby with the condition. This risk depends on whether the first case was due to:

• Trisomy 21 (random event) – The recurrence risk is about 1%.

• Translocation Down syndrome (inherited) – The risk is significantly higher if one parent is a translocation carrier.

Genetic counseling can help assess the risk for future pregnancies.

Mosaic Down syndrome is a rare form where some cells have an extra chromosome 21, while others have the normal 46 chromosomes. It occurs due to an error in early embryonic cell division.

Risk Factors for Mosaic Down Syndrome:

• It is usually a random event with no known preventable risk factors.

• In rare cases, a parent may have mosaicism in their reproductive cells, increasing the likelihood of passing Down syndrome to their child.

• Genetic testing can help detect parental mosaicism.

There is no way to prevent Down syndrome entirely, but certain steps can help parents make informed decisions:

• Prenatal Screening and Diagnostic Testing – Tests like nuchal translucency ultrasound, non-invasive prenatal testing (NIPT), and amniocentesis can assess the risk during pregnancy.

• Genetic Counseling – Parents with a history of Down syndrome can consult a genetic counselor to understand their risks.

• Family Planning Considerations – If maternal age is a factor, some families may choose to conceive earlier.

While Down syndrome is primarily caused by random genetic events, advanced maternal age, parental genetic translocation, prior pregnancy with Down syndrome, and parental mosaicism are key risk factors. Understanding these factors allows for informed reproductive choices and better prenatal care. If concerned about the risks, consulting a healthcare provider or genetic counselor can provide personalized guidance.