The family of a teenage boy who died after being diagnosed with motor neurone disease (MND) has warned the rare, degenerative condition can hit “anybody at any age, at any time”.

Kyle Sieniawski, 14, from Pontypridd, Rhondda Cynon Taf, died on 27 November, after being diagnosed less than a year ago with MND.

The disease typically affects people aged over 50, and Kyle is believed to be the youngest person to have died with MND in the UK.

Former rugby league star Kevin Sinfield, who is currently running seven ultramarathons in seven days for MND awareness, told Kyle’s family the “community” will be there for them, and Kyle “will always be remembered”.

Kyle’s mum, Melanie Sieniawski, told BBC Breakfast: “It can affect anybody at any age, at any time.

“They need [to do] as much fundraising and awareness as they can – to get a cure as soon as possible.”

His father, Mark, said the family wanted to keep raising awareness.

“To be honest what Melanie and I went through was horrific”, he said, describing his son’s condition as “horrendous to watch”.

In January, aged 13, Kyle was diagnosed with MND after he began losing mobility in his arm.

His condition deteriorated rapidly, and he was subsequently left unable to use any of his limbs.

Following his diagnosis, Kyle’s family said they were “desperate” to bring him home from hospital but were unable to do so because their property could not be adapted to meet his needs.

His parents and brother, Liam, spent more than nine months living with him at Noah’s Ark Children’s Hospital in Cardiff.

He relied on a breathing mask and feeding tube, and was moved into intensive care last month after developing an infection.

Kyle’s family described him as “brilliant” and a “troublemaker”, adding “his personality shone right through”.

Mr Sieniawski said the teenager “was a fighter”, and had received visits from many others affected by MND while in hospital.

“They all thought he was brilliant,” he said.

“He touched so many people, to be honest. He was amazing.

“He had banter and laughter with everybody. We had so many strangers come to visit him. They all thought he was amazing.”

Ex-Leeds Rhinos rugby player Sinfield met Kyle’s family at Gorseinon Rugby Club, Swansea, midway through his latest MND fundraising challenge on Wednesday.

The 45-year-old took on the challenge in honour of his friend and former teammate Rob Burrow, who died with MND in June last year.

Sinfield began the 7 in 7: Together challenge in Bury St Edmunds, in Suffolk, on 1 December, and is undertaking seven ultramarathons across UK to Ireland, before concluding the challenge in Leeds on Sunday.

He is running at least 45km (27.9 miles) each day of his challenge, in bursts of 7km (4.3 miles).

In south Wales, he took time out to meet Kyle’s family on the third of his ultramarathons, with hundreds of wellwishers joining him for part of the route through Swansea.

“We’ll run a bit faster and harder this leg,” he told Kyle’s family.

The player-turned-rugby coach hopes to raise £777,777 – in honour of the number seven shirt worn by Burrows – to add to the more than £10m he has raised since 2020.

Following their son’s death last week, Kyle’s family said in a statement: “Kyle fought with everything he had, but in the end it all became too much for him and he very sadly passed away.”

“We’re just completely heartbroken.

“Kyle… we’ll miss you so very much buddy and we love you more than words could ever possibly say.”

MND affects nerves found in the brain and spinal cord, which tell your muscles what to do.

This leads the muscles to weaken and stiffen over time and ultimately impacts how you walk, talk, eat and breathe.

It is a relatively rare condition, and is most commonly diagnosed in people over 50.

A person’s lifetime risk of developing MND is one in 300; about 5,000 adults in the UK will have the disease at any one time.