The US authorities have begun an investigation into the death of Abubakar Nadama, 5, who lived in Batheaston, Somerset.

He underwent three rounds of chelation therapy at the Advanced Integrative Medicine Centre in Pittsburgh, Pennsylvania, at which point his heart stopped, according to Deputy Coroner Larry Barr.

Staff at the centre tried to resuscitate him but he was pronounced dead.

More tests will be carried out to determine the precise cause of his death.

Marwa Nadama, the boy’s mother, said that she did not hold the therapy responsible for her son’s death.

Rufai Nadama, the boy’s father, who works at the Plymouth Hospitals NHS Trust as a specialist registrar in respiratory medicine, remained at work in Britain while his son, wife and 11-year-old daughter moved to the US so that Abubakar could receive the treatment. He has flown to America to be with his family.

Neighbours in Britain said that Abubakar’s parents were determined to do anything they could to improve their boy’s condition. Carers visited the family in Batheaston three times a day and his diet was strictly controlled in an attempt to reduce the severity of his autism.

Some believe that autism can be linked to a mercury-containing preservative that was once commonly used in childhood vaccines. Chelation therapy involves injections of ethylene diamine tetra-acetic acid, a synthetic amino acid which acts by sticking to heavy metals that are then flushed out of the body in the urine.

The treatment has been available in the US for several decades and if Abubakar’s death was directly caused by chelation therapy it will be the first such fatality since the 1950s.

The US Food and Drug Administration has approved chelation only for acute heavy-metal poisoning that has been confirmed by blood tests.

Critics maintain that there is too little evidence to link autism to mercury or lead toxicity.

Howard Carpenter, the executive director of the Advisory Board on Autism-Related Disorders, said that it was just a matter of time before there would be a death linked to the therapy. “Parents of children with autism are desperate. Some are willing to try anything,” he said.

Autism, a neurological disorder in which sufferers have difficulty in communicating, socialising and empathising, has no known cure, at least according to mainstream medical opinion.

The first signs of the condition can become apparent within a few months of birth, but is more usually diagnosed when a child is three or four.

In Britain the condition was tentatively linked with the measles, mumps and rubella vaccine (MMR) in the 1990s, causing widespread concern among parents.

The research that prompted the link has since been discounted and a succession of large-scale research projects has failed to establish a link between MMR and autism.

Nevertheless, some parents remain concerned enough that they refuse to allow their children the MMR vaccine, which has in turn caused an increase in measles outbreaks.

A post-mortem examination on Abubakar proved inconclusive yesterday and it could be several months before investigations into the cause of his death are completed.

Gary Swanson, a child psychiatrist at Allegheny General Hospital in Pittsbugh, who works with autism patients, said of the treatment: “I can’t sit there and endorse it as a viable treatment. It’s not something published in peer review journals and studies.”

Unofficial estimates suggest that in 2000 only a dozen autistic children were treated with chelation therapy but that the figure has now risen to 10,000.

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