"There is a relationship between autism and seizures; as many as 40 percent of children and young adults with autism may experience seizure and adolescence is a particular time of vulnerability," said Dr. Bryan King, the director of child and adolescent psychiatry at Seattle Children's Hospital's Research Center for Health Services and Behavioral Research.
"There are hormonal changes that could increase the risk of seizure, and certainly there are ongoing brain changes that take place during adolescence, but no one knows why the risk increases in older children."
Regardless of the cause, Ossi said that the family is now grieving. He added that the incident "is the worst pain any parent can experience, the loss of child."
Speaking for John Travolta, Ossi said, "This is the worst day of his life."
Ossi said that Dr. Mark Smith, the Travolta family doctor, plans to give a statement after the autopsy.
In multiple interviews, John Travolta and Preston have always attributed their son's illness to carpet-cleaning products they once used in the house.
"It was about seven years ago, and I was obsessive about cleaning -- his space being clean, so we constantly had the carpets cleaned," John Travolta told Larry King in 2001. "And I think, between him, the fumes and walking around, maybe picking up pieces or something, he got what is rarely a thing to deal with, but it's Kawasaki syndrome."
"Jett's whole immune system shut down and he got really sick with high fevers -- 104 and 105. He developed a rash on his body and swollen lymph glands -- it was horrible," Preston told the U.K Mirror in 2004.
"Clearly, if anything about Jett's death could reflect badly on Scientology, the organization will go to great lengths to handle the problem," Kent said.
Scientology, the religion that John Travolta has followed for about two decades, believes psychiatric drugs and counseling cause damage.
In a 1999 news conference about his movie "The General's Daughter," Travolta disputed assertions that TV and films encourage kids to commit violent crimes and instead linked their cause to drugs.
"My personal thinking is that some of these murders have to do with drugs -- psychiatric drugs, street drugs," he said. "They've found a lot of common denominators are things like Prozac that are altering people's states of mind."
Preston, John Travolta's wife, also came to Cruise's defense in 2005, when he was criticized for his public attack on Brooke Shields for using psychotropic medication to ease her postpartum depression.
Late Monday, in a statement to ABC News, the Church of Scientology responded to critics who claim it does not promote medical treatment.
"Scientologists seek conventional medical treatment for medical conditions," the church said in a statement. "Scientologists use prescription drugs when physically ill and also rely on the advice and treatment of medical doctors. The Church does not involve itself in the diagnosis or classification of any medical condition."
ABC News' Eileen Murphy, Lauren Cox and Kirk Fernandes contributed to this report.