What IS Down Syndrome? Part I of III
I’ll be the first to admit — before having Luke, I could never have explained to someone what Down syndrome actually is. In turn, I think my lack of education made facing his diagnosis even more daunting because it seemed so unknown. Author H.P. Lovecraft says it perfectly — “the oldest and strongest emotion of mankind is fear, and the oldest and strongest kind of fear is fear of the unknown.”
My plan for the next few posts is to help make Down syndrome less unknown, to help people learn and understand what it is and what it means for those individuals who have DS. I encourage you to ask questions in the comments or send me an email so in later posts, I can address your questions and together we can help others see that a Down syndrome diagnosis is not something to be feared.
So, what exactly is Down syndrome? To understand DS, we first have to go back to basic science you learned in high school — chromosomes contain your body’s genes, the blueprint and foundation of your body. Typically, humans have 46 chromosomes — 23 of which come from the mother and 23 of which come from the father. In individuals with Down syndrome, there is an extra chromosome present (either partially or fully), which means they have 47 chromosomes instead of the typical 46.
You may also hear Down syndrome as being called Trisomy 21. A ‘trisomy’ is medical terminology which simply indicates an extra copy of a chromosome is present, and the number 21 is because the chromosome that has the full or partial extra copy is the 21st chromosome. While Down syndrome is not the only genetic condition in which an individual has an extra chromosome, it is the most common chromosomal disorder, occurring in approximately 1 out of every 700 births in the United States which is equal to approximately 6,000 babies born every year who have Down syndrome.
There are three different types of Down syndrome: Trisomy 21, mosaicism, and translocation (I’ll go into detail on those next week). However, no matter the type, an individual with Down syndrome still has an extra copy of chromosome 21 present in their body. The extra copy of chromosome 21 can come from either parent, or it can be a random occurrence in cell division at conception.
The full and exact cause of why this triplicate happens is not known. It is a common misconception that babies with Down syndrome are only born to mothers over 35 — 80% of babies born with Down syndrome are born to women under 35 simply because women under that age have babies at higher rates. What is true, is that women over the age of 35 do become more at risk for a variety of complications during pregnancy, including having a baby with a chromosomal abnormality.
Down syndrome can be diagnosed one of two ways – prenatally, or at birth. With a prenatal diagnosis, that means that while a woman is pregnant tests are performed to determine if any defects or genetic conditions are present. Screening tests (such as ultrasounds and blood tests) do not give an exact yes or no answer whether or not Down syndrome is present, they simply give a likelihood or a probability. On the other hand, there are diagnostic tests (amniocentesis and chorionic villus sampling [CVS]), which can give a much more definitive answer and are nearly 100% accurate. A birth diagnosis occurs when a baby is born and certain physical traits are observed or complications arise. The physical traits are things such as:
Decreased or poor muscle tone
Short neck, with excess skin at the back of the neck
Flattened facial profile and nose
Small head, ears, and mouth
White spots on the colored part of the eye (called Brushfield spots)
Wide, short hands with short fingers
A single, deep, crease across the palm of the hand (Simian crease)
However, because some of those physical features could be present in babies who do not have Down syndrome, a genetic karyotype (which is an analysis of the chromosomes) is done by obtaining a blood sample and then examining the cells. If you read Luke’s story, then perhaps you will remember that we kind of had a little bit of both a prenatal and birth diagnosis. We were alerted to the fact that he could have Down syndrome while I was pregnant because of the screening tests, but it wasn’t confirmed until after his birth when we got the results of his genetic karyotype.
Next week, I’ll be covering more about Down syndrome and going in depth on the three different types of DS. Enjoy a cute picture of Luke as a reminder that, while he does have Down syndrome, Down syndrome does NOT define him.
Stay well, friends!