Michael and Brian are so high functioning that all the medical professionals we came in contact with were sure they had “Mosaic Down syndrome”. After the umpteenth time hearing this, I decided I needed to find out if, in fact, they were and to investigate what that meant… exactly. Please note: Some of what I have written here is factual and some is my interpretation of those facts. So bear with me:
Here’s what I garnered from my research — To my medical providers’ surprise, Michael and Brian have “typical” Trisomy 21 Down syndrome… Not mosaic.
“Typical” Trisomy 21 Down syndrome is characterized by the presence of extra chromosomal material in the 21st chromosomal pair. This error is replicated as cells split and multiply during fetal development. When blood samples are taken, this extra chromosomal material is present in some very high percentage of the cells that are tested. That is, nearly 100% or 100% of the cells tested have the extra 21st chromosomal material.
“Mosaic” Down syndrome is also characterized by the presence of extra 21st chromosomal material. However, when blood samples are taken, this extra chromosomal material is present in some number less than 100% of the cells that are tested.
Now, here’s the thing. I also read that if you test blood samples from different areas of the same individual — the leg, stomach, or brain, for instance — that the % of cells with the extra chromosomal material varies according to where the sample was drawn from. That means that somewhere during the body’s developmental processes, the duplication error either accidentally stopped copying the extra material (undoing the original error), OR that the duplication error happened later in development so the cells that developed before the error was made were unaffected, OR that the ultimate destination and role of any particular cell may, or may not, repeat the duplication error… such that not all the cells in the body will necessarily carry the extra chromosomal material and may, thererfore, be less or unaffected.
Interestingly, I read many comments by parents whose children were diagnosed “Mosaic DS” who said they wished they had not been lead to believe that their children would automatically be higher functioning because not all the cells had the extra chromosomal material. Many of these folks found that their “mosaic” children had the same, similar or as many developmental issues as the children with “typical” Trisomy 21 Down syndrome. Logically, if there’s significantly less extra 21st chromosomal material overall then one might think the chances are better that the individual would be less affected. However, where this extra chromosomal material attaches itself complicates that assumption.
Medically-speaking, we can see how many cells contain the extra 21st chromosomal material. However, (here I go again on my soap box) because research shows that developmental and environmental factors drastically influence the outcome… how much and where the extra 21st chromosomal material attaches itself as well as hormonal responses to and environmental factors acting upon the individual — including exposure, teaching methodology, nutrition, medical intervention, family treatment and societal treatment — NO ONE CAN KNOW THE OUTCOME OR PREDICT THE LIMITS OF A PERSON WITH DOWN SYNDROME!
Ya Gotta Believe!