Justin and Charlotte Meek were two peas from the same pod.

The brother and sister both had smiles which glowed and minds as bright as two shiny buttons.

"Little characters," says their mother Wendy. "Happy, smiley and the loveliest kids."

However, they also shared something that has no name, a rare genetic twist of fate which doctors have yet to fully diagnose or find a cure for.

Both children had issues with their bowels and could not walk. They had limited speech and required growth hormone injections.

It is a potentially life-limiting undiagnosed genetic disorder, and it already cost Justin his life when he was just ten-years-old.

Now his little sister is carrying on the hope for a cure.

Charlotte and Justin are SWANS - syndromes without a name. Now six and a half, it has been three years since she had to say goodbye to her big brother.

However, Justin's blood has been kept, in case it can help with the search for a cure for his little sister.

Although Charlotte's older sisters, Caitlin and Sophie are very protective of her, one of the biggest challenges of caring for a child with a rare disease is how difficult it can be to find support.

Charlotte's mother Wendy knows this better than most, so much so she has become a parent representative for a charity called SWAN - offering support to families affected by a syndrome without a name.

Today, on February 28 - the official Rare Disease Day - Wendy and Charlotte are at a hospital in Glasgow with other families for a party celebrating the children who have brought them together.

"SWAN is really supportive, the group have been there for me during the hard times," says Wendy.

"I think when you have a child who is undiagnosed, you don't have a support group you can turn too.

"This group are all completely undiagnosed conditions but some have similar symptoms - this can be a major help to parents.

"You feel quite isolated as a SWAN family because you struggle to even get professionals to understand let alone anyone else - but another parent, with a child with a similar symptom, that can make a big difference having them to talk too."

Charlotte has a potentially life-limiting undiagnosed genetic disorder - she cannot walk or weight bear, she has limited speech, Global Developmental Delay, Hypotonia, bowel problems and requires growth hormone injections.

Justin had all of these issues and also oxygen dependency.

In Charlotte's case, she has been lucky enough to be one of 1000 patients put forward for the Scottish genomes study which could help find a full diagnosis and a cure.

"We have hope," says Wendy. "We're only six months in, but we've had every genetic study you can have up until now."

When Justin was born he became blue and lifeless and spent most of his first year in hospital.

Wendy and her husband Stephen realised quickly that something was wrong but despite a lot of tests and professional input their little boy remained undiagnosed.

"When Charlotte was born, my mother's instinct told me something was wrong but the doctors weren't in agreement until she was about ten-months-old and failed to meet her milestones," says Wendy.

"Again lots of tests were done and came back clear so we knew everything it wasn't but there was no diagnosis.

"Without a diagnosis a lot of the time the professionals don't know how to treat issues and don't know how to advise us - they simply don't know the answers.

"It makes it much harder to access support and resources and can leave you feeling very scared and isolated."

SWAN UK have worked to double their membership to help more families like Wendy's - who is now the sole charity representative in Scotland.

"Swan has been an absolute lifeline, I wanted to become a parent rep so no other families felt that way and had someone to talk too," she says.

"You have people who just get it. I want to spread the word to families and professional to have a better understanding of undiagnosed children."

Justin would have been 14 this year. He passed away from an unexpected blood clot in his stomach 2014, while the family were on holiday in Florida.

His little sister Charlotte still shows as much courage as her big brother. The determined young girl learned to get about by bum shuffling and always shows her sheer determination to be happy.

Her mother, ever proud, is keen that a diagnosis will come through soon for her daughter.

"I would personally love a diagnosis so I would know what might lie ahead and why things ended the way they did for Justin," she says.

"We obviously fear that the condition may result in us losing Charlotte too.

"Despite the knowledge we have we still cannot access support like hospice care for Charlotte as we have no diagnosis so no prognosis."

However, Wendy's work with SWAN this year is something she is very much looking forward to.

"SWAN UK has truly been a lifeline to me - it offers a friendly ear, and has helped to stop me feeling isolated.

"Without SWAN UK we never fitted in anywhere because of the lack of diagnosis.

"it is important that things continue to improve for families with rare, genetic and undiagnosed conditions."