my grandson’s fragile x test report is normal. What else can be cause of his autism? Any help?
As Binary says it is quite unlikely that you will be able to find out the cause of your grandson's autism. There's lots of research into causes of autism, but with the exception of Fragile X, it's not possible to be sure about why individual children are autistic.
Here's a link to an article summarising recent thinking about causes of autism:
You might find this comparison of Fragile X and autism helpful too:
Thank you for the information.