Happy twins Grace and Emily Hitchens share the same beautiful brown eyes, but their lives are separated by a cruel genetic illness which rarely lets children reach teenage years.

Eight-year-old Grace has Neimann Pick Type C – a condition which eats away at the brain’s control of body functions – and which took the life of her elder brother Harry in 2010 when he was seven.

But Emily is a bright, active normal schoolgirl with no trace of the genetic problems suffered by her sister.

Grace and Emily were born to parents Carl and Fiona before Harry’s condition had been diagnosed.

And now NPC – which affects only 50 children in the UK – is tightening its grip on Grace’s abilities, said their dad at their home in Eldwick, Bingley.

“Whereas two years ago Grace could talk and babbled on happily, now she can no longer say mummy and daddy,” said Mr Hitchens, 47, a precision tool maker.

“She was walking and eating perfectly normally, but now that’s fading and in the last month she has lost the ability to use a straw.

“NPC has affected her differently to Harry, who stayed mentally very bright and aware for longer, but it affected his body even more swiftly.”

Despite her increasing disabilities, Grace is clearly a happy girl who still enjoys many outside activities. Mum Fiona, 49, said: “She still goes to Brownies at Cottingley and to Chellow Heights special school in Bradford, which she really enjoys.

“But her favourite thing is swimming at Shipley Pool with her grandad.”

Before their daughter’s abilities weaken any further, Mr and Mrs Hitchens are determined to take the twins on a magical trip to Florida where Grace can swim with dolphins while she still can – and pay a visit to Walt Disney World.

Both parents gave up high-flying jobs in computer electronics to care for their family. But tough financial times due to caring for first Harry, and now Grace, mean they are desperately raising funds for the trip scheduled for “as soon as possible”, said Mrs Hitchens.

Emily, a star pupil at St Joseph’s Primary, Bingley is doing her bit with a sponsored 45-minute swim at Bingley Pool on Monday – three days before the twins’ ninth birthday Mrs Hitchens said: “We set up Grace’s Wish in November to try to raise £12,000 and have already had tremendous support from the local community – people are so kind.

“That money will also go to buy a specialised bike for Grace and any extra will go to the national NPC charity.

“We just want to give her the chance of doing this magical thing – it really will be the trip of a lifetime for Grace and our family.”

Details of how to help with fundraising are available at www.graceswish.co.uk/home/. Her late brother’s story is at www.graceswish.co.uk/brother-harry-s-story/.