Fok Mei-ling leans forward and plants a kiss on her son's cheek. He starts to laugh.
Howard Fok Hin-yeung's laugh is not accompanied by a smile, because other than being able to move his eyes from side to side, none of the muscles in his face work. But a staccato sound emanates from his chest.
Howard is 13. He is good at maths, has a great sense of humour, and should have died at least 10 years ago.
He suffers from spinal muscular atrophy (SMA), a severe neuromuscular disease of which there are three types.
Howard has type one, the biggest genetic killer of children under the age of two.
Howard is the oldest type-one SMA sufferer in Asia - his survival due to a mixture of aggressive medical intervention, home-help, and the love and sheer bloody-mindedness of his mother.
'The fact that Howard is alive is a medical miracle,' says Ms Fok.
'He has the most severe type of spinal muscular atrophy. He can't eat, can't breathe independently, can't talk and can't look down with his eyes.'
SMA does not affect sufferers' intelligence but they are trapped in a body that cannot move because the muscles are paralysed.
'SMA is a recessive gene and one in 40 people is a carrier. One in 6,000 babies are born with SMA,' says Ms Fok.
Howard lives at home, rather than in a hospital like most other children with his condition.
He is the first child with a ventilator to attend school in Hong Kong. He goes to the John F. Kennedy Centre in Pokfulam three times a week.
He communicates through a software programme on his laptop that his occupational therapist has loaded with words and phrases to suit different situations.
With his family, he communicates with sounds through his breathing equipment.
Howard's fragile health means that he cannot pursue a full-time education. Mrs Fok sits in the school canteen while he is studying so that in the event anything goes wrong, she can be on the scene quickly.
'Now that we know the genetic cause, the medical profession is working aggressively to find a cure,' she says.
Mrs Fok set up the Families of SMA Charitable Trust six years ago, and 70 children are registered.
She and her doctor husband have home help, but there are many families who do not have this kind of resource.
'I felt that although Howard is doing well, I had this compelling need to help children in his position, because of my experience with SMA.'
These children require 24-hour care, to be turned in their sleep every two hours, bathed and changed. Through Operation Santa Claus, the trust is requesting funds for helpers so children can live with their families.
Mrs Fok says Howard has changed her life for the better.
'Howard has really changed my life completely. Before I had Howard, I was an ambitious lawyer trying to climb the corporate ladder in an international law firm. After I had Howard, I felt there was so much more to life than spending 24 hours on your career,' she says.
'I cherish each day with Howard, watching him grow up to be a fine young boy from a fragile sick baby. He's survived his prognosis and I think they should rewrite the medical books. SMA is not a fatal disease, even if it is non-treatable.'