A better understanding of the genetics of autism would be of huge value to parents such as Julia Young, who struggled for years to establish the cause of her young son Alex’s behavioural problems.

While Alex, now 12, was apparently normal at birth, his development began to regress around the age of 14 months, soon after his sister, Jess, was born.

“The more the baby crawled and babbled, the less Alex spoke and the more he withdrew,” said Mrs Young, of Bognor Regis, West Sussex.

At Alex’s nursery school, the staff soon began to wonder whether he was deaf. “When you called his name he would not listen to you, he would just carry on doing what he was doing,” Mrs Young said. “If he was painting he would stay painting, and if you asked him to come out of the sandpit he would stay there.”

She took Alex to speech therapy, with no results, and nothing could be found wrong with his hearing. At his first school, his odd and inexplicable behaviour continued.

“He would not sit with the other children - he would sit with his back to the class, but still answering questions. He would not line up when told to, and he would just leave the classroom to go to the toilet without asking.

“His behaviour at home became more and more erratic. He would cross the road in front of cars. He would suddenly turn the hot water on and almost scalded himself. He had no sense of danger.”

At the age of 5, Alex was finally referred to a child psychiatrist. “We had been there for five minutes when he told us that Alex had high-functioning autism.”

Alex’s symptoms are at the less extreme end of the autistic spectrum, but he shows many of its classic signs. “He gets a word in his head and keeps repeating it, trying to get me or his sister to say it,” Mrs Young said.

“He gets obsessions that can last for a year. At one point he was obsessed with Thomas the Tank Engine, and wouldn’t do anything unless we could link it to trains.

“Now he is obsessed with his Play-Station, and with the band Muse. Every time we go in the car, he wants to hear Muse records, and he knows all the words.”

Family history suggests that genetics could be involved. Mrs Young herself has had attention deficit disorder diagnosed recently and her niece’s son has attention deficit hyperactivity disorder. Both often coexist with autism. Alex also has two uncles who have suffered from epilepsy.

Mrs Young said she would welcome genetic insights that help diagnosis, but also worries about where genetic screening could lead.

“It took an age to get Alex the help he needed,” she said. “The earlier you know, the better, and if this could help us identify autism as young as possible it would be wonderful.

“But I would not want a situation like Down’s syndrome, where you tell parents while the child’s in the womb and you have to make a decision.

“We also ask ourselves how much of Alex’s personality is Alex, and how much is the autism. Can we even separate the two?

“If you asked us could we have prevented it, we would have to think. Obviously in some ways it would be better for him, but he is happy in himself.”

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