We had our boys tested for Fragile X. With hindsight, we shouldn't have bothered. Fragile X tends to have a different profile and is not generally associated with high IQ.
A problem with genetic testing - they can only do it to look for specific things. It is not a cover-all screening. They can look for general chromosomal breaks, missing bits etc (macro malformations) but to look for specific faulty genes requires specific and far more expensive genetic testing, and only can deal with genes for which there is already a specific test. For example, you can't yet test someone's DNA to determine if they have blue eyes or red hair. You can't determine someone's blood group from genetic testing, not yet. Because there are easier tests as a rule for these things, nobody has bothered to go to the trouble to develop a genetic test. Why test the DNA for blue eyes if all you have to do is look? And blue eyes or not isn't vital information for someone's health.
So don't go in expecting magic answers, or even comprehensive answers. The most they can tell you, is if your child's DNA is complete, or if there are bad breaks in the chromosomes which MIGHT explain things. Or it might not.
A common thing in increasingly detailed medical testing - "seek and ye shall find". What I mean is, when you go digging, you find stuff. But is what you find relevant? Often it is not, but when you are looking, it is easy to 'blame' what you find, when it could be completely unrelated.
For example, I had to have a chest X-ray before I started uni (a bit like blood tests before marriage - not something we've ever done here in Australia). In my case, the X-rays showed that I have a couple of vestigial ribs in my neck. They're not causing me any trouble. But if I had gone in with neck pain and had the X-ray, it would be easy for someone to say, "Aha! Those ribs must be causing the pain!" I have since had neck pain, but I do not believe my ribs are the cause.
The other thing to consider - if you get a result that says, "Something is out of the ordinary," what can you do with the information? How can you use it? Even if all you do is say, "Now we know what it is," for some people this is a help. Or if you can say, "At least we know it is NOT a chromosomal abnormality," then you have excluded one more possibility, which means fewer remain.
It can be expensive to do this, and the results can be disappointing, especially when you realise that medical science is still in its experimental infancy when it comes to genetic testing.
I was tested for trisomy 21 in the baby, among other chromosomal abnormalities, when I was pregnant with difficult child 3. I was not permitted to refuse the test. I did not want it because I did not feel the knowledge would change anything. The test was expensive and we had to wait weeks for the result. It was a relief to know we did not have a baby with a chromosomal defect, but of course it did not warn us of his autism. They also would not have identified Fragile X, because they would not have been looking for it. That is why we had to test for it again, 6 years later.
Marg