What is Mosaic Down Syndrome?
In typical cases of Down syndrome, the cell does not split properly. Instead of every cell having 46 chromosones, they have 47 chromosones. In the case of Mosaicism, the cell starts to split properly but then something misfunctions and a percentage of the cells split into 47 chromosones while the rest split typically into 46. (Another theory is that the cell starts out diving into 47 chromosomes, but then some of the cells correct the error. I believe the former theory is now what is currently accepted in the scientific community.)
A good explanation of Down syndrome characteristics I once read said that SEEMS almost is as if a lot of the cells develop more than 90% of the way but not all the way, so a typical defect is a hole in the heart that SHOULD have grown over.
With Mosaic Down syndrome or Mosaicism, like with typical Down syndrome, there is a broad spectrum of effects. For example, Amelia does not have too many facial features from the Down syndrome, it’s hard for people to notice unless they know other people affected by this. Some of her cells will grow out of it – such as blood, which regenerates. Apparently the presence of 46 chromosone genes trumps the 47’s and cell regeneration knocks them out.
Of course, certain cells don’t regenerate, like brain cells. With each organ, it’s a crap shoot that cannot be determined without a biopsy.
I will be frank: this used to be more important to me. That Amelia has this rare type of DS means that she is less susceptible to certain aspects of DS. For example, she never had hypotonia, the hole in her heart was never an issue (cleared up on its own), and she spoke VERY early. But just like regular Down Syndrome, kids with Mosaic Down syndrome run the continuum from less affected to more affected. I feel it more understandable to others to just say she has Down syndrome. She does have some learning disabilities and sinus issues and is extremely tiny and we have to keep monitoring her heart. I don’t want to be a freak about her having or not having this or that. I want to see her as she truly is, so that I can help her progress where she can and accept where she can’t. In my opinion, that’s the very best we can do as loving, interactive parents.
To learn more about Mosaic Down Syndrome, here are the very few resources out there: