I have marfans syndrome. A major symptom is a deformed chest. The odd chest is the main reason that I made a trip to the doctor and that is when I was told that I had marfans. My chest caves in around the sternum atleast an inch. Limits how far my lungs can expand out so at times I do get short of breath. In high school I did play basketball and many games I stayed on the court for the whole game. If you are in good shape then you can overcome some limitations from marfans. I am also really tall compared to my parents. Im 6ft4 but only weigh 150lbs so I am really thin for my height. Really just cant put on the weight and the doctor said that it might not be a good thing to put on weight.
If he does have marfans then i would have to say that it isnt an extreme case. He is still muscular and doesnt seem to have any extreme disformaties.