Fiona has a type of Down syndrome called mosaic Down syndrome. Only 1-4% of all people with Downs have this form of it, different sites have told me different numbers. Mosaicism is very under studied. People with mDs have a percentage of cells with an extra copy of the 21st chromosome and the remaining cells are unaffected.taken from INTERNATIONAL MOSAIC DOWN SYNDROME ASSOCIATION In less complicated terms, only some of her is effected by Down syndrome. Mosaicism occurs in about 1-2% of all people with Down Syndrome. In this type of Down Syndrome the error in separation of the 21st chromosome occurs in one of the first few cell divisions AFTER fertilization. This causes the fetus to have some cells with 46 chromosomes and some with 47. The cells with 47 chromosomes have one extra 21st chromosome. Because of the fact that not all cells contain the extra chromosome 21 the range of physical problems varies depending on the ratio of cells with 46 chromosomes to those with 47 chromosomes. taken from HERE
The fact that she has such few physical markers has always been something that intrigues me. I google images of people with Downs, searching for others who have the syndrome but look fairly "normal" ( I absolutely hate using that term, but its politically correct). I didn't find many, but I found some. The thing with mDs, is it is still just as unpredictable as Down syndrome. There is still a wide range of mild to severe cases. It all depends on how many of the person's cells have trisomy-21. And it also is not possible to know which cells are effected unless each and every organ is tested. That is just a lot of testing for something that, frankly, doesn't really matter. People with mosiac have the same health risks that full Downs have- the fact that Fiona had a heart condition actually implies that she has quite a lot of cells effected. Which still tells us nothing about how "severe" of a case she has. Her whole body could have T-21 except for her brain, and she could be very high functioning, or just her brain cells could have T-21 and she could be very severely mentally handicapped. So mosaic doesn't necessarily mean she will be high functioning. It does, however greaten her odds.
Another sweet child with mosaic Downs. Same big, just slightly almond shaped eyes as Fiona.
There was a study done in 1991 by Fischler and Koch where they measured the IQ of 30 people with Down syndrome, some with the mosaic form, some with the usual T21. The study found that the IQ of the folks with mosaic down syndrome averaged 10-30 points higher than the others, and they speculated that this is because fewer of their cells have 3 copies of chromosome 21. The problem with drawing a conclusion from the study, though, is that the causes of Down syndrome are not simple. Not everybody expresses the same genes equally, or develops the same characteristics, even with exactly the same chromosomes! In the study I just mentioned, there was a lot of overlap in the samples; some of the people with Trisomy 21 outperformed their mosaic counterparts on the same IQ test, and vice versa. - image and info taken from BLESSED-WITH-DOWN-SYNDROME.ORG
We will learn more about Fiona's condition as she grows and developes. As of right now, she is a beautiful, high functioning little baby. And although she is slightly behind developementally then peers her age, shes not that far off track. I mean, I guess we can give the girl some slack- she did have to go through heart surgery :)
To learn more about mosaic Down syndrome, visit THE INTERNATIONAL MOSAIC DOWN SYNDROME ASSOCIATION