According to actress Sharon Epatha Merkerson (Radio's mother in the film) there is no name for what is wrong with him; it's almost certainly a genetic disorder because his father and his younger brother have a similar developmental disability. There are reviews stating that Radio displays the DSM-IV symptoms of Autistic Spectrum Disorder as well as developmental/intellectual delays.
Radio is a film in 2003, which is about the story of James Robert Kennedy (played Cuba Gooding Jr.) a developmentally challenged man, who in the mid-1970s spent his afternoons walking past the local high school football field in the small town of Anderson, South Carolina. Cuba Gooding Jr. won Best Actor at the 2004 NAACP Image Awards for his performance for this film.
New findings hint at why autistic children are more interested in objects and ideas than they are in other people. Learn more at TIME.