In the complex world of genetics, our understanding of certain conditions, including Down Syndrome, is still evolving. While chromosomal abnormalities tied to Down Syndrome are broadly known, its precise cause remains a mystery. However, we have managed to pinpoint and outline some of the top risk factors for Down Syndrome in a baby.
The CDC reports that 1 in 700 newborns now have Down syndrome, a condition marked by a wide range of physical and mental impairments. Even while scientists have identified the specific chromosomal defects that lead to Down syndrome, they still don’t know what causes them.
Kenneth Rosenbaum, M.D., founder of the division of genetics and metabolism and co-director of the Down Syndrome Clinic at Children’s National Medical Center in Washington, D.C., says, “For the most part, we simply don’t understand [Down syndrome causes] as well as we would like.” Because of this information gap, it can be hard to determine if you are at risk for having a child with Down syndrome. Read on to discover what raises your risk for Down syndrome and how it is caused.
Down Syndrome’s Causes
Knowing what chromosomal abnormalities lead to Down syndrome can help parents prepare for the possibility that their child will be born with the disorder. In the nucleus of every human cell, 46 chromosomes (clusters of genes) are present at birth. Chromosomes pair up, with each parent contributing 23 (egg) and each parent contributing 23 (sperm). When a baby is conceived with an extra copy of one of these chromosomes, namely chromosome 21, the result is Down syndrome.
Experts Have Identified Three Subtypes of Down Syndrome
- Trisomy 21: Trisomy 21 is a genetic condition in which a person has an extra copy of chromosome 21 in every cell instead of the typical two. Nearly all people with Down syndrome have trisomy 21.
- Mosaic Down syndrome: Some cells have the typical two copies of chromosome 21, whereas others have a third copy due to mosaic Down syndrome. Only about 2% of people with Down syndrome have mosaic features.
- Translocation Down syndrome: A person with translocation Down syndrome has an additional piece of chromosome 21 that is connected to another chromosome and two complete copies of chromosome 21 in the cell. This arises due to translocation in 3-4% of people with Down syndrome.
Contributing Factors to the Probability of Down Syndrome
Although Down syndrome is inherited, it is unlikely that you would have a close relative with it. According to Dr. Emily Jean Davidson, clinical director of the Down Syndrome Program at Boston Children’s Hospital, “the extra chromosome seems to happen by chance” in most cases.
Having a kid with Down syndrome is not guaranteed, but there are ways to raise your chances. Here are four potential risk factors for having a child with Down syndrome.
Parents of any age can conceive a child with Down syndrome, but the risk rises with maternal age. There is a one in 1,200 chance that a woman of 25 will have a child with Down syndrome. At age 35, the odds are 1 in 350, and at age 40, they are 1 in 100.
The National Down Syndrome Society reports that by age 45, the likelihood of having Down syndrome has increased to 1 in 30. Genetic advice from their partners could be helpful for women over 35 who want to have children.
Maternal folate metabolization
Studies have shown that some expectant mothers of children with Down syndrome have an abnormal folate metabolism, but this has not been conclusively linked to the syndrome.
The maternal folate metabolism hypothesis has been proposed, although there is as much research disproving it as supporting it.
There is no genetic basis for either trisomy 21 or mosaic Down syndrome. However, one-third of cases of translocation Down syndrome are inherited, as the National Down Syndrome Society reported. This represents about 1 in every 1,000 people who have Down syndrome.
To determine whether the translocation originated in the newborn (which is the most likely scenario) or whether either parent is an unaffected carrier, doctors will typically recommend chromosomal testing for both parents of a baby diagnosed with a translocation. If this is the case, genetic testing can reveal each individual’s underlying reason and the likelihood of a future recurrence.
According to the National Down Syndrome Society, the risk of having another child with translocation Down syndrome is 3% if the father carries the chromosome and 10% to 15% if the mother does.
The risk of having another kid affected by trisomy 21 or translocation Down syndrome is roughly 1% if you already have one child with the disorder.
Remember that the factors that lead to Down syndrome are already there before conception, regardless of the risk you face. That is to say, no matter what you do during your pregnancy, it won’t change the outcome. During pregnancy, all you can do is take good care of yourself and the baby by eating right, getting plenty of rest, and following other basic health guidelines.