My son was recently tested for Fragile X. He is what they call a mosaic, he has some of the premutation and some of the full mutation, but is not considered to have Fragile X syndrome. They can't prove that this is why he has PDD, but they think it is the reason. My mom and I were both tested and we are both premutation carriers and never knew it. I just had another baby and he doesn't have the Fragile X gene at all. So in my PDD son's case, it is genetic. It has been in our family for generations probably and no one ever knew until now.