Kevin is a wonderful character. He absolutely has some health problems, but the great thing is that Kevin simply refuses to let any of his problems stand in his way . . . ever. Kevin's medical issue is that he has Morquio Syndrome. This means that he is unable to metabolize a special type of sugar called glycosaminoglycans. This sugar type is integral in the body's growth and development of bones, cartilage, muscle, and tendons. Because Kevin can't break down this sugar, he winds up with a number of physical problems like a short stature, joint issues, spine problems, and heart problems. Kevin's medical problems are tied into another problem of his. He struggles socially to make friends. He struggles mainly because he looks so different. He's an outcast, and that is probably why he and Max get along so well. They are both outcasts. Finally, I would say that a third problem that Kevin deals with is his vast intelligence. He's super smart, and that is a wonderfully good thing; however, Kevin is absolutely smart enough to know that his disease is killing him. Max doesn't know this kind of thing, but Kevin knows what his final fate is most likely to be. He has to struggle with the knowledge, and he has to struggle with staying as upbeat and positive as he does throughout the novel.