If Nia Wyn could keep only one moment in her life it would be her feeling when her son Joe Alexander was born on August 29, 1998, at 1.07pm.

At that instant, she says, “heaven landed inside me”. Joe’s skin was the colour of pearl. Alex, her photographer husband, could not take his eyes off his wife and baby and the room was spellbound.

Two hours and nine minutes later and Wyn’s life had changed for ever. At 3.16pm, Joe was wheeled hurriedly by nurses to intensive care, his bewildered parents scrambling behind. Later he was diagnosed with severe cerebral palsy.

Doctors told the grief-stricken couple that he would not walk, talk or see. “He won’t even know you,” a medic summed up.

Up to that point Wyn’s life had been an effortless trajectory, tracking through an idyllic childhood, a career as a journalist, marriage to Alex and a longed-for first pregnancy. The girl that a schoolfriend said looked like Marianne Faithfull had enjoyed, as her mother put it, “the luck of the gods”.

However, Joe’s diagnosis opened the door to a world that Wyn struggled to make sense of. Along the way she kept daily jottings, noting if anyone said anything that eased the pain. “I would reflect on them, a bit like self-help.”

The result is Blue Sky July, Wyn’s account of her life with Joe up to his seventh summer. All the milestones and sacrifices are contained in this book: the desperate round of alternative therapies she embarked on, the break-up of her marriage – Alex wanted balance, Nia just wanted to “heal” her baby – the impossibility of returning to her newsroom job.

Chronicled, too, are the breakthroughs that Joe made under his mother’s watchful eye. She stopped giving him the damaging drugs that he had been prescribed for epilepsy, convinced (rightly) that he did not need them. Hopeful that Joe had the potential for sight, despite an eye doctor who insisted for three long years that he didn’t, Wyn was vindicated when it was discovered that Joe had cataracts – easily removed.

In these pages are Joe’s first words – “more” – and later, as he lies with Nia under a cloudless sky, “blue” – hence the book’s title. Here is the first hug and the first time he swam out of his mother’s arms in a heated pool.

Joe, it turns out, is clever and Wyn battles to get him into the local Beavers group, where he wins badges, and to Meadowlane, a mainstream primary in Cardiff, where he is the first child to have a physiotherapist come to the classroom to treat him.

The book ends on a high note: with the leavers assembly at Joe’s nursery school, Craig-y-Parc, where his parents watch as he sweeps onto the stage to collect a silver cup, awarded to “the child that has come the furthest”.

Today Wyn is sitting in her Cardiff living room and making new plans for her son, now aged nine. The wheelchair Joe whizzes around on in the house is neatly folded, the special taxi will bring him back from school in a few hours’ time.

“Joe still has cerebral palsy,” says Wyn. “He uses a wheelchair. We have not had those kind of miracles. But the undercurrent of what has happened is a miracle. Love and stimulation made a difference.

“Early on at the hospital I said, ‘What do we do?’ My dad said, ‘Well, we just love him’. We started from that point. You realise that is all there is really.”

It’s an extraordinary story – but what moves most is how Wyn has subverted the way much of the world insisted on seeing her son. “Sinners” shouted Cardiff kids at special needs children. “Every mother’s worst nightmare,” said one girl who visited Wyn early on. “You are brave,” said another. Disability, special needs, shadows and darkness.

Wyn does not try to pretend that Joe’s situation did not hurt, especially when she looked at the “perfect” children of her university girlfriends and her two siblings (four apiece).

What she ends up capturing, though, is a love story shot through with instants as funny and golden as any before his birth. “The most profoundly beautiful and exquisite moments I’ve ever had have been those I spent with Joe,” she writes.

She records his breakthroughs on white cards pegged to a silver birch twig, they lie on the floor of their home kicking the door between them, he shouts, “Ta ra, luv” at her – the Cardiff-speak his elderly helpers have taught him. And she marks the years by the flowering of a vine of roses over the window.

“You move from a place where you feel it is the end of the world to a place where you feel almost privileged,” she says.

Blue Sky July, much of it written in the dead of night (Wyn had to stay up to turn Joe to ease his aching muscles), was first produced by Seren, a tiny Welsh publisher. But its success – particularly after it was featured as Radio 4’s book of the week – prompted Michael Joseph to snap it up. Wyn will promote next month’s reprint in New York and three companies are considering the film rights. “Meg Ryan to play me, perhaps,” laughs Wyn.

Joe will stay at Meadowlane until he is 11, then Wyn wants to take him on a gap year – visiting different countries to sample world music. “Music is Joe’s great passion,” she explains.

After that? She’s not sure. There is a “wonderful” boarding school in Surrey for children with cerebral palsy. But she would prefer a local secondary school: “I would be reluctant to be separated from him.”

Soon Alex, who comes to see Joe once a week, will take him on an activity weekend with his primary school “doing boys’ things”.

“He’s a really good father,” says Wyn. “The split wasn’t about Joe. Every week I would be driving to Cirencester to do the cranial osteopathy. Then I would find something else, like massage. We had routines going five times a day with his eyes. Spend three years like that, something had to happen.”

I tell her that one sentence in the book brought me up short. In the hospital to have Joe’s cataracts removed, Wyn watches a mother visiting another patient, the disabled child she has surrendered to foster care. She cradles him and Wyn writes: “Mothers who leave and mothers who don’t, we’re all the same.”

How does she justify that? “There can be 100,000 reasons why someone reacts the way they do to the same situation,” says Wyn.

“I could see her absolute love for this child. I wasn’t looking to judge anyone. It’s so hard sometimes. I was looking for something that makes meaning of the situation.”

She crosses to the music centre and clicks a CD into the deck. After reading her book, an old colleague turned up out of the blue with a song he had written. The music drifts through the room: For every heartache, and every tear that falls, For every bridge crossed – It’s Blue Sky July “That’s it”, she says, as she mimics Joe singing along to “his” pop song with an imaginary microphone, “that says it really.”

Blue Sky July is published by Michael Joseph. All author royalties go to the Joe Alexander Trust

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