The Relationship Between The Age Of The Mother And The Risk Of Down Syndrome In Her Child
Down syndrome or trisomy 21 is a widely known disorder that affects about 0.14% of babies born annually. The risk of a mother bearing a child with this chromosomal disorder exponentially heightens with the mother’s age. This is why child birth at an older age gives not only risk to the mother, but also the child. Besides down syndrome, the risk of other abnormalities and diseases do arise with the age of the mother. However, people with down syndrome are able to live relatively normal lives. For example, the Paralympics features many athletes with this condition. Danny Rumsey is a Paraolympian for Team Australia who’s won several awards. In addition to athletics, people with down syndrome also are able to find jobs and obtain an education.
Trisomy 21 means a third chromosome in the 21st chromosome. As known, humans have 23 pairs of chromosomes and a total of 46 chromosomes. In a cell, chromosomes are typically jumbled up and not “in order”. A karyotype can be created to isolate and view these chromosomes in order. The largest on is chromosome 1 while the last ones are the x and y chromosomes (sex chromosomes: XX are seen in women and XY are seen in men). In other words, a karyotype is an organized chart of chromosomes listed and labeled in order for observational purposes. It shows the 22 chromosomes with the sex chromosomes, each being only one pair. When a karyotype is created for a person with down syndrome, the 21st chromosome is seen with three chromosomes instead of 2. This is the case for all people with this genetic disorder. Other genetic disorders can also be seen with a karyotype. For example, triple X syndrome has three X chromosomes instead of two and this will be seen in the karyotype. Other disorders similar to down syndrome and triple X exist as well.
A child born with down syndrome has many opportunities to live a normal life. However, they do have complications to face. People with down syndrome have lower levels of muscle tone and have slower development rates. It takes children with down syndrome longer to learn to walk and move. They also have abnormal attention spans, require speech therapy due to slow development in learning and also run the risk of having heart and vision abnormalities. Physical symptoms of down syndrome include a shorter neck, flatter face (nose included), short hands, and smaller facial features. People with this disorder have an average lifetime of sixty years.
This genetic disorder can usually be predicted during the fetal stage of pregnancy with a few tests. Two important ones include a blood test and amniocentesis. This process involves an ultrasound first before obtaining a sample of the amniotic fluid that surrounds the fetus. This sample can be used to test many conditions and one of them includes down syndrome. It is also used to detect the sex of the fetus. Typically this is done when the ultrasound shows abnormalities, there are concerns around the pregnancy and the child, and to relieve the mother of risks. During the first trimester, OBGYNs typically check for the likelihood of such genetic diseases and also the risk of them. By the second trimester, the known likelihood becomes clearer. If the woman shows risk of bearing a child with this genetic disorder, the amniocentesis test is performed.
So why does the age of the mother affect the chances of the child having an abnormality in the 21st chromosome? This goes into the biology behind females. Unlike males who constantly produce millions of new sperm cells all their lives from puberty on, females are born with a set amount of eggs. Because these are sex cells, they do undergo meiosis which has two parts: meiosis 1 and meiosis II. Egg cells are arrested in metaphase I of meiosis I until puberty. During puberty, one egg will begin to develop in the stage called ovulation. The egg does not undergo meiosis II until or if there is fertilization. While males have new sets of sex cells every second of everyday, females have the same set throughout their lives, until menopause. From this, it can be observed that the eggs age with the mother. Something that is arrested at a stage for a long period of time is more prone to a disorder due to the age. In this case, the disorder is in the division of chromosomes.
Since the age of the mother does affect the risk of down syndrome in her child, why do women choose to have children later and later in life? In 1950, the average age of a new mother was 21.4 years old. Today, the average age of a new mother is about 26.3 years old. This statistic was obtained in 2014. There are many reasons the age of mothers has risen rapidly: from the improvement of quality and accessibility of birth control, to pursuing careers and education, to simply just choosing to settle down first, and the list continues. Some ways women are avoiding this increased risk of genetic diseases includes freezing eggs or having a surrogate mother; however, these are not economical choices. Some ideas in the future include genetic engineering to eggs, ingesting or injecting nutrients into the body to nourish the eggs to stay healthy, and to find better alternatives or ways of freezing egg cells without the high cost.
References:
https://www.cdc.gov/ncbddd/birthdefects/downsyndrome.html
https://www.healthline.com/health/down-syndrome/down-syndrome-facts
https://www.genome.gov/genetics-glossary/Karyotype
https://medlineplus.gov/lab-tests/down-syndrome-tests/
https://www.mayoclinic.org/diseases-conditions/down-syndrome/symptoms-causes/syc-20355977
