The author of "Cloud Atlas", David Mitchell remembers the day he read the memoir of a 13-year-old boy with autism -- hailing it a "revelatory godsend" that offered a window on the life of his autistic son.
Mitchell said Naoki Higashida was "one of the most helpful and practical writers on the subject of autism in the world."
"Pre-Naoki, I'm ashamed to say that I used to regard and treat my son as a kind of defective robot," Mitchell told AFP.
Higashida was just five years old when he was diagnosed with severe autism. Autism is a spectrum of neuro-developmental disorders that manifests itself in difficulties communicating.
The exact causes are unknown and research suggests it may be genetic, environmental, or both. There have also been unproven scares linking the condition to childhood vaccinations.
Like Dustin Hoffman's autistic character in the Oscar-winning film "Rain Man", Higashida, now 22 years old, gets stuck repeating certain movements, twitches erratically and sometimes recites numbers.
He has trouble expressing himself and gets flustered when there are too many people around him, but can communicate well -- though sometimes clumsily -- by spelling out his thoughts on a keyboard-like alphabet grid.
- The Reason I Jump -
"I can't explain my feelings well because I have autism, but I can communicate by doing this," Higashida told AFP in an interview at his office in Kisarazu, southeast of Tokyo.
"Words are not just a means of communication, but my friends," he said.
That friendship with words blossomed into an essay, entitled "The Reason I Jump", which was published as a book in 2007 featuring 58 often-asked questions about his autism and his frank -- sometimes startling -- answers to them.
"I very quickly forget what it is I've just heard," he writes in response to a query about why autistic people repeat questions.
"A normal person's memory is arranged continuously, like a line. My memory, however, is more like a pool of dots. I'm always 'picking up' these dots -- by asking my questions."
Addressing the book's title, he writes: "When I'm jumping, it's as if my feelings are going upward to the sky. By jumping up and down, it's as if I'm shaking loose the ropes that are tying up my body."
The book was a hit in Japan, but its discovery and subsequent translation by Mitchell -- who previously lived in Japan and has a Japanese wife -- brought it mainstream audiences all around the world.
"We read a chapter and thought, 'My God, that's like our son talking to us' or 'Jesus, that's what our son does,'" the author, who is based in Ireland, told AFP by email.
"He?s not a guru, and not a saint -- but he knows a hell of a lot about living with an autistically wired brain," said Mitchell.
Mitchell's English translation was published in 2013 and soon topped the bestseller list of Amazon's British and US sites, according to Higashida's agency.
His book subsequently hit the shelves in more than 20 other countries, including France, Germany, Hungary, Italy, Norway, Romania, Sweden and the Netherlands, having been translated into more than a dozen languages.
Some specialists say Higashida is not typical of people with autism and caution that others with the condition should not be judged against him.
Toshiro Sugiyama, a Japanese psychiatrist, said Higashida's talent for writing makes him stand out from others living with the condition.
"He is capable of speaking for other people with autism," he said.
"His work offers a window into autism for wider society," said Sugiyama of the Hamamatsu University School of medicine.
- 'No need to compare' -
Experts estimate that around one in a hundred people are somewhere on the autistic spectrum; however, the ratio varies enormously, with definitions and medical support dependent on the country.
"Levels of knowledge about autism in Japan are still lower than those in the United States or Britain," said psychiatrist Kosuke Yamazaki, who is chairman of the Autism Society Japan.
Naoki's mother, Miki Higashida, is only too aware of the battle that autistic children and their families face every day.
"When he was a child, I struggled a lot and tried to force him to be normal," she said.
"But I have stopped comparing him with (others). I'm happy to see him find his own world" in writing, she said.
"Now I can think Naoki is Naoki. There is no need to compare," she added.
Her son is now an accomplished author, with 18 books to his name, ranging from fairy stories to non-fiction, and he regularly writes for the Japanese edition of the Big Issue.
For David Mitchell, this is heartening.
"I hope he will continue to write, and turn his experience of the world and his thoughts and his journey through life into words," he said. "As long as he writes, I'll read him."