Re: How is it that hes just a carrier?
I think that fragile x has a lot of behavioral symptoms - did the dr. ask you questions about behavior? Perhaps the dr. felt that your son did not fit the behavioral definition of fragile x. I don't know details but if you feel uneasy, call the dr. back for more details or even get a second opinion. Good luck.
The important thing is getting the services that your son needs ie speech therapy, occupational therapy, a good suitable school program if he needs a self contained classroom, or understanding trained in autism teachers if he is in an inclusion pre-school. The school district has a responsibility to provide this for your son and the director of special ed can give you the information.