Mothers of children diagnosed with Marfans Syndrome

Hello, my oldest son's father was diagnosed with Marfans Syndrome at age 31. I have told my pediatrician that, but he said that he did not think my son had it. I have done a little research, but I'm confused. I understand that many of the patients are what my doctor referred to as 'funny looking'. My son looks like a normal boy. He isn't abnormally tall or anything like that. I've heard that if he does have it then he may not show any symptoms until like age 10. He is 7 now. I've also been told that high impact sports are kind of out of the question if he is diagnosed with it. Should I force the issue with the pediatrician to have my son conclusively tested? Is there any advice or words of wisdom that any of you mothers can share?