What IS Down Syndrome? Part III of III
Now that we have covered what Down syndrome is and what causes it, I want to go a little deeper (without giving you a headache) and explain what the extra copy of chromosome 21 means and what it does in the body.
Chromosome 21 is the smallest of all the chromosomes, and is one of the only chromosomes in which having an extra copy present is not devastating to the individual. It is responsible for approximately 2% of the total amount of DNA in our cells, and contains between 200-300 genes that provide the blueprint for certain proteins and functions in the body. To try and put it simply, the presence of an extra 21st chromosome causes the overexpression (over production) of those genes, which is what leads to some of the conditions that are more commonly seen in individuals with Down syndrome.
A question that I have gotten many times since talking more about Luke and Down syndrome in general is: what are some other medical concerns someone with Down syndrome can have? While there are, of course, no set-in stone medical concerns that an individual with Ds is guaranteed to have, there are some conditions that are called “co-occurring” because they are more frequently seen in individuals with Ds. I’ve listed a few of the most common co-occurring conditions below, feel free to read a more comprehensive list here.
Heart defects: nearly 50% of babies born with Down syndrome have some type of congenital heart defect, there are three types of heart defects that are more commonly seen, and some require surgery to repair. Because these types of defects are seen more frequently, if Down syndrome is suspected during pregnancy then fetal echocardiograms are done to screen for any cardiac issues, and after birth an echocardiogram is done again within the first month of baby’s life.
Hearing loss: it is estimated that almost 75% of children with Down syndrome experience some hearing loss, which can be associated with structural problems within the ear. Babies with Down syndrome receive the same hearing screening at birth as all other babies, but they also have those screening tests retaken every 6 months for the first 3 years of life to monitor for any hearing problems that may arise.
Hypotonia: nearly all children with Down syndrome have some amount of decreased muscle tone, which is partly what contributes to developmental delays in things like rolling, sitting up, and crawling. Decreased tone can also lead to feeding issues for babies. Working with a variety of therapists as needed from a young age can help significantly with addressing issues of low tone, and ensure that the individual is getting the support they need to continue with proper development.
Digestive problems & Celiac disease: There is a wide range of potential digestive problems that can occur in individuals with Ds, ranging from actual anatomical issues to problems with digesting certain foods. Celiac disease (an autoimmune disease caused by a reaction to gluten) affects up to 16% of individuals with Down syndrome, and because it can cause such a wide variety of problems, it is recommended that children with Ds are screened for Celiac disease between the ages of 2-3.
Interestingly enough, while that extra little chromosome can cause a few different conditions to be more common, it also reduces the likelihood of certain other conditions. For example, it is rare for individuals with Ds to have heart attacks, experience a stroke, or develop solid organ tumor cancer (such as brain or lung cancer). Research also shows that, while congenital heart defects and childhood leukemia are more common in individuals with Down syndrome, they are also more likely than those with the typical number of chromosomes to make a full and fast recovery.
Ultimately what I hope you take from this post is not that Down syndrome is scary or a medical burden. More so, I hope it opens your eyes to see the unique and highly complex way that our bodies work. It is estimated that only 20% of fetuses with trisomy 21 reach full term, which points to the fact that those who grow to term actually have highly effective genomes that may even function better than the genomes of those of us with 46 chromosomes, simply because their bodies have to adjust for the disruptions that the extra chromosome causes and it has to do so automatically. No wonder having a baby with Down syndrome is called being a part of “the lucky few”. As always, here’s our little lucky charm!