The Saint Clair County coroner says the southwest Illinois junior high school student who died after suffering a medical emergency during a basketball practice had heart disease.  The Belleville News-Democrat reports coroner Rick Stone identified the 13-year old boy as Demetrius Simpson on Thursday.  Stone said an autopsy conducted Thursday revealed the eighth grader died of hereditary heart disease.  District 90 Superintendent Douglas Wood says Simpson went to the bathroom during training Wednesday at Fulton Junior High School for his basketball club and didn’t come back.  He says Simpson was found there later in distress and was taken to a hospital.