We both feared we might get dementia but never dreamed that our young girls would...

Parents tell of heartache over rare cruel disease

and over again. And I’d have to tell her something three times, before it sank in. Mark and I felt like she was regressing. She’d come out of school covered in food, unable to feed herself properly. It just wasn’t right.”

The worried couple, of Letchworth, Herts, sought medical help and were initially advised their daughter had ADHD.

But a neurologist at London’s Great Ormond Street Hospital carried out tests and Emily was diagnosed with NP-C in spring 2001. The pair both carry the defective gene that causes NP-C, meaning their children had a one in four chance of developing it. Lisa added: “We had no idea we were carriers. Now we were told Emily would be lucky if she lived beyond her teens.

“It was absolutely devastating to hear that our child would keep regressing to a point that we would lose her so young.

“We cried and cried for Emily, for all the things she would be robbed of… boyfriends, a husband, children of her own. The list was endless. It was very tough. Our life changed beyond recognition. “We had to move house three times to cater for her needs, while trying to give our other kids the best childhood we could.”

The girls also have an older brother Harry, now in his 20s, who does not have NP-C. Former warehouse worker Mark and Lisa were dealt another terrible blow when Sarah, aged 10, started showing the same symptoms. She once vanished from the family home with their dog Bow, only to be found confused, standing by the side of a main road by Mark. Lisa said: “Like Emily, she needed a lot of support at school, she struggled in class. “Mark turned to me and said, ‘We need to know.’ Deep down, I think we knew. “I think that’s why, when Sarah was finally diagnosed at Great Ormond Street Hospital in 2008, I didn’t react.” Sarah’s condition soon deteriorated, leaving her confused and with increasingly erratic behaviour.

During one family trip to Southend when she was 11, she disappeared and was found on a roller coaster alone. She would also shout

At six months and, right, in respite care shortly before she died