Not all autistic people suffer from brain damage. MRI and CAT scan shows the damages in the brain. No one knows what cause autism. My son is 22 with autism. His brain shows no abnormality. Parents and relatives always feel guilty about their autistic loved ones. I always try to remember what I did wrong to cause my son to be autistic. But his brother is not autistic and lived under the same environment. Don't blame your brother, just accept your nephew and give him as much love as you can. God bless you and good luck.