The twins helping scientists break new ground

Genetically identical siblings can shed a unique light on the understanding of mitochondria and aid research into treatment

- James Tapper

The rash Lucia Magee had on her hand was barely noticeable. "It was really just redness," William, her father, said. "If she hadn't been a twin, we might have just concluded she had red fingers.

But the absence of the rash in Lucia's identical twin sister, Isabella, made their parents suspicious.

Two years later, the five-year-olds have formed an important part of groundbreaking research at Great Ormond Street Hospital (Gosh) and University College London (UCL) that may help scientists unlock treatments for several illnesses, including Parkinson's and Alzheimer's.

What the Magees now know is that Lucia has a rare muscle disease, one her genetically identical twin sister does not have.

The family had not heard of juvenile dermatomyositis (JDM), the illness Lucia was eventually diagnosed with. Few people have. It's a rare autoimmune disease that is detected in about two in a million children each year. After the rash appears, it starts weakening muscles, so children seem more tired than usual.

"The reason it's so serious is that a child can become extremely weak to the point where they can't swallow properly," said Lucy Wedderburn, a professor at UCL and a paediatric rheumatology consultant at Gosh.

If the condition is left untreated, it can harm the brain, lungs and gut, which, Wedderburn said, could even burst. For some children, JDM is fatal.