I can't link to any sites about RTA - but basically Reactive Attachment Disorder is an inability to form bonds with those close to you. Often they remain very social with those they do not know, and are sometimes seen as social butterflies, but they have trouble forming any kind of meaningful bonds with family, pets, etc. and do not really have very many "close" friends. Behavioral symptoms include attitude, threats (against others and themselves), and blowups over the most trivial of things.
In the case of this family member, his birth mother took him home from the hospital and never fed him or even changed his diaper and basically was just waiting for him to die, his birth grandmother called CPS and saved his life, but that early life rejection by the mother who was suppose to love him is likely what triggered it in him.