Associated Press A rare genetic variation dramatically raises the risk of developing autism, a large study showed, opening new research targets for better understanding the disorder and for treating it. Research into the causes of autism has focused on genetic causes because so many families have multiple children with the disorder. Thus far, only about 10 percent of autism cases have a known genetic cause. Boston-area researchers estimate the gene glitch they've identified accounts for another 1 percent of cases. They found a segment of a chromosome which has genes linked to brain development and various developmental disorders was either...