A mother and father were today being questioned on suspicion of murdering their terminally-ill son.

Jacob Wragg, ten, had Hunter syndrome, a genetic disorder which dramatically affects mental and physical development.

Police and an ambulance arrived at the family home in Henty Close, Worthing, on Saturday at 11.20pm after a 999 call was received.

Jacob was treated at the address and taken to Worthing Hospital where he was pronounced dead.

His parents, Mary and Andy, both in their 30s, were arrested on suspicion of murder.

They appeared before a specially-convened hearing at Chichester Magistrates Court yesterday evening when police were granted permission to further detain them for 36 hours.

A post-mortem was carried out but Detective Inspector Nigel Brown, heading the investigation, today declined to reveal how Jacob died.

Friends of Jacob's family were in shock today.

One said: "Jacob was the oldest of two boys. He was a lovely lad but it was dreadful for everyone knowing he was going to die from this Hunter syndrome.

"Mary shouldered much of the care and Andy played his full part in supporting Jacob.

"Jacob had been very poorly of late and he was in respite care on a regular basis. Andy was really cut up about Jacob, knowing what his condition meant. It was a huge strain for them both and the whole family."

Former soldier Mr Wragg recently returned from Iraq where he worked in private security. He previously served in the Merchant Navy and was a member of the crew of the QE2.

His father Bob said: "Jacob died on Saturday night and Mary and Andy have been arrested.

"We haven't been able to speak to Andy or Mary at all. We hope we can later today."

Henty Close, a small, quiet cul-de-sac, off Henty Road, Worthing, was sealed off by police this morning.

Police cars and vans were parked outside the family's semi-detached home, one of ten in the close.

Only a postman on his bicycle was allowed into the close to deliver mail.

Curious neighbours in Henty Road, who were unaware what had happened, repeatedly asked officers what was going on.

But the officer guarding the entrance to the close said: "I'm afraid I can't comment at all."

He said officers were still carrying out house-to-house inquiries.

Four years ago Mary Wragg raised money for a mercy mission to South Africa to help a child who has the same disease as her son.

She wanted to visit Lynn Pienaar and her stricken son TJ, aged nine.

She said: "Lynn saw a story about Jacob and she just rang me.

"TJ is deteriorating rapidly and I just want to be there for her to give her some moral support."

Last year Jacob's younger brother George presented Princess Alexandra with a bouquet at the opening of Chestnut Tree House, the children's hospice near Arundel where Jacob received respite care.

Jacob's mother and other parents worked several years to help raise the £5 million needed to open the facility.

Mrs Wragg said at the time: "The benefit to us will obviously be the respite care, allowing a break for Jacob and myself."

Hunter syndrome is a rare and incurable genetic disorder caused by the body's inability to produce certain enzymes.

The disorder affects about one in 150,000 boys. If a mother is a carrier, there is a 50 per cent chance any boy born will suffer from the illness.

Children with the most severe form are not expected to live past their teens.