Helena Huxham could dance with her eyebrows, says her mother. At 3 she could do extraordinary things on the computer. She played hide and seek with her twin sister, even though she could barely move, closing her eyes and inviting her family to ask where she was. “In the wardrobe?” they would ask. “No.” “In the fish tank? In a helicopter? Are you sitting next to me?” “Yes!” she would reply, her eyes open. Again and again.

There is no doubting the joy that Helena brought to her parents, Lilias and Max, and to her twin sister Saskia. She was, her mother says repeatedly, a happy child. Yet Helena was also profoundly ill and from the moment that spinal muscular atrophy 1 (SMA) was diagnosed when she was four and a half months old her parents knew that she would become paralysed and die. “It’s not an if, it’s when,” as Lilias puts it.

Inevitably during the next three years they faced agonising decisions about their daughter’s treatment and as they have followed reports of the legal hearings surrounding baby “MB” — who also has SMA — they have felt empathy for his parents and their instinct to prolong their child’s life. Judge Holman has enabled this with his ruling that MB’s life “does still have benefits and . . . should be allowed to continue”.

So, while the judge also gave doctors the right to withhold painful emergency treatment, he has enabled MB to continue to live in hospital supported by a ventilator. The Huxhams took a different decision for Helena, preferring that she should live at home without a ventilator, although as Lilias explains, the family’s choice was one that evolved as Helena’s illness progressed.

When the twins were born in 2000 Helena was alert and quick to smile within the first few days. At about ten weeks Lilias, who is a paediatrician, noticed that she seemed floppy and was not moving one leg properly. The diagnosis came to her suddenly some weeks later when Helena was referred to a neurologist near the family’s home in Sheffield.

“It’s very easy to deny what’s going on and not think rationally when it’s your own child,” Lilias says. “Then when we were waiting for the appoinment with the neurologist it hit me what the diagnosis was. She looked like a photograph of a child I’d seen in a text book. They call it a frog-like posture but there’s the very alert facial expression. I got a tendon hammer and checked her reflexes. She didn’t have any. There was no kidding myself from that point on.

“I looked at text books and the prognosis leapt out at us, which was inevitable death. Eighty per cent die within a year, the remaining 20 per cent within the following year, so death by two years. You can imagine what a completely shattering moment that was. You’re just numb and, I think, in a state of complete shock for two or three weeks. The neurologist confirmed the findings and we could see there was nothing else that could be done.”

Helena was well at that point. Her muscles were weak but she could lift her limbs a little, and she was bright and happy, her mother says. But her condition deteriorated and when, at eight or nine months, she began to find feeding distressing a nasogastric tube was fitted. For the rest of her life she was tube-fed and regularly suctioned to remove the saliva she could not swallow.

On a few occasions when she had infections she was taken to hospital, and it was these visits that began to shape the Huxhams’ view of how she should be treated.

“During one episode, when she was 10 months old, she was heading for the intensive care unit and she was terrified. Parts of her lungs had collapsed and she was struggling to breathe. The medics thought she would pull through if she was ventilated and we would have accepted ventilation then. But fortunately I stayed up with her all night stroking her head and calming her down and she managed to get herself through it,” says Lilias.

“She spent a week in hospital, had lots of physio and oxygen and got better. But it was a terrifying experience for us and for her. She didn’t enjoy being in hospital and we didn’t either. Around that time we started to face up to the fact that the inevitable was going to happen and you start thinking about what you should do next time. You read about other people who’ve been through it. I remember one story that said it’s easy to put a child on a ventilator but often when it becomes futile it’s the parents who have to make the decision and that’s the most heart-rending and difficult decision you can make.

“We didn’t want to be in that situation. We felt very strongly that we wanted Helena to die at home and not have to come off a ventilator in hospital. Having said that, we wanted to do everything we could to prolong her life. She was such a joy.”

With equipment supplied by the NHS, the Huxhams turned their home into “not quite an ITU”. Lilias gave up work and, with the support of their family, nurses were hired. “She needed a high definition of care. She needed suctioning 60 times a day or more. You never knew if she was going to choke. If you were going to leave the room you’d suck her before up you left and you wouldn’t go very far because she used to cough very quietly and you needed to hear. As she got older she asked for suctioning, it was very quick, ten seconds.”