Image caption Blaze need daily medication

"Arthritis isn't something you think a two-year-old could have."

But that was the explanation Kelly O'Sullivan was eventually given for her two-year-old daughter Blaze's unusual symptoms - a rash that covered her body and swollen joints that stopped her wanting to walk.

Kelly, from Bolton, says Blaze had a normal birth and developed normally, walking when she was a year old.

But Blaze became ill in January this year when she was 18 months old.

Kelly says: "At first she got a rash all over her and a high temperature and she didn't want to walk.

"I took her to the doctor and she was given lots of different medicines, antibiotics.

"Then she started walking with a limp, and it got progressively worse and her knee swelled up to the size of a tennis ball."

Doctors thought Blaze's symptoms were caused by a viral infection, but then she began to experience stiffness in her neck and this time was referred to her local hospital.

Kelly said: "They still thought it was a viral infection. She was in there for about four weeks, and given intravenous antibiotics. Lots of doctors from different specialties saw her."

However there was still no diagnosis - and Blaze was moved to Manchester Children's Hospital where another raft of tests, including a lymph node biopsy and a bone marrow test, were carried out.

Finally - in March - she was diagnosed with systemic juvenile idiopathic arthritis (JIA).

'She shouldn't miss out'

JIA refers to a group of arthritic conditions that affect children. All cause inflammation, but relatively little is known about them and how they will progress.

Any problem usually starts before a child is five, and affects more girls than boys. An estimated 12,000 children in the UK have a form of arthritis.

Some only have a short-term illness, while around a third continue to have symptoms into adulthood - but it is hard to predict how an individual's illness will progress.

There is so little known Prof Wendy Thomson,, CAPS study

Kelly said she was pleased that Blaze had a diagnosis at last - but surprised.

"I didn't know a two-year-old could get arthritis. It's not something you think they can have."

Blaze now has to have daily and weekly injections and takes steroids to control her symptoms.

Kelly, who also has a two-week-old baby, says the medication is helping but Blaze cannot lead a normal toddler's life.

"She should be able to run around like any normal toddler. And I can't get her into a nursery because one of the drugs she takes, methotrexate, affects the immune system and they won't take her.

"I'm trying to get her a place though, because she shouldn't have to miss out."

'Worth it'

Blaze is one of over 1,300 children taking part in a study overseen by the University of Manchester, and backed by the charity Arthritis Research UK, which aims to find out more about JIA.

Geneticist Prof Wendy Thomson, who is one of the researchers working on the study, said: "There is so little known. Parents often say there's a lack of information about what might happen to their child."

Children in the study, which began in 2001, are followed up annually to the age of 16, with subsequent checks at the age of 18 and 21.

Kelly said: "When it was explained they they didn't know much about the illness and wanted to find out more, I decided to get involved.

"If that helps another family in the future, rather than them having to go through months waiting to find out what it is, it's worth it."