John Travolta told yesterday of his desperate attempts to save his dying son after he suffered a seizure at their holiday home in the Bahamas — and acknowledged publicly for the first time that the boy had suffered from autism.

Accompanied by his actress wife, Kelly Preston, the Grease star appeared in a court in Nassau to recall the horrifying moment that a male nanny, Eli Wheaton, came pounding on their bedroom door to rouse them from their sleep on January 2 to report that 16-year-old Jett was lying unconscious on the bathroom floor.

"I ran downstairs with my wife to help my son," Travolta told the judge and jury, who are hearing evidence against a local politician and an ambulance driver accused of trying to blackmail the star for $25 million in a plot related to Jett's death.

On reaching the bathroom, Travolta saw his boy — who also had a rare inflammatory disease known as Kawasaki syndrome — stretched out on the floor showing no sign of life. Travolta, who appeared in court grim-faced, explained how he immediately sprang into action to try to revive the teenager. "Jeff, the other nanny, was doing some compressions. I was doing the breathing," he said.

Speaking so quietly that at one point he was asked by the judge to speak up, Travolta confirmed what had long been rumoured in Hollywood but never been discussed in public by the family. "My son was autistic and suffered from seizure disorder. Every five to ten days he suffered seizures which lasted 45 seconds to a minute," he revealed.

His reference to autism was all the more remarkable because of Travolta's belief in Scientology, a religion considered by many to be a cult. One of the religion's tenets is that mental illness is psychosomatic and can only be realistically treated through spiritual healing. Scientology does not recognise autism as a real affliction and shuns psychiatry as a "pseudo-science", putting Travolta's admission yesterday at odds with a church in which he is a leading figure.

Travolta, 55, and Preston, 46, both looking sombre and dressed in black, had arrived at the courthouse flanked by police officers and minders after flying in to the Bahamas aboard their private jet from their home in Ocala, Florida. It was believed to be their first trip back to the islands since Jett's death, which occurred during a New Year break at the Old Bahama Bay resort on Grand Bahama, where Travolta owns four connecting apartments.

His testimony, which was set to continue last night following a short adjournment, is considered key to the prosecution's case against Tarino Lightbourne, a paramedic, and Pleasant Bridgewater, a former senator, who are charged with trying to extort $25million from the actor by threatening to go public with a document relating to Jett's medical care.

The document was a waiver releasing the ambulance crew from liability after the actor allegedly declined to have Jett rushed to a local hospital and asked instead for him to be driven to the airport so he could fly him back to Florida for treatment instead.

Taking a deep breath, wiping his brow and shifting uneasily on his feet as he leaned on a podium in the courtroom, Travolta described how his wife had cradled Jett's head as he and the nanny frantically tried to bring him round.

When an ambulance arrived around 35 minutes later, by which time Jett's carers had resorted to using a defibrillator to try to jump-start his heart, the teenager was placed on a gurney and loaded on board. "I spoke with the ambulance driver and asked him if he would take us to the airport," Travolta said, admitting that he then signed a liability waiver handed to him by Lightbourne but did not pore over the detail because "time was of the essence."

Whatever was discussed, Travolta ultimately agreed that Jett should go to the local hospital. It is believed that Lightbourne, using Bridgewater as an intermediary, threatened to make the document public after Travolta's commitment to the Church of Scientology became the subject of public debate in the days after Jett's death, with many questioning whether treatment of the boy's long-standing medical condition had been inhibited by his parents' beliefs.

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