Thousands of British children afflicted with a painful and crippling disease could have their lives transformed by a drug currently reserved for adults, research suggests.
Up to 2,500 children in the UK under the age of 16 suffer from systemic juvenile idiopathic arthritis (JIA), also known as Still's disease.
A new study today showed that the condition of children with the disorder improved by up to 90% after 12 weeks of treatment with a drug that targets the immune system.
The antibody drug tocilizumab, marketed as RoActemra, is at present only licensed for adults with moderate to severe rheumatoid arthritis.
Makers Roche hope the drug will be approved for British children with systemic JIA within two years.
The disease causes joints to become swollen and painful and also leads to a rash, fever, fatigue and weight loss. In severe cases internal organs such as heart, liver and spleen may be damaged.
Most children affected begin to show symptoms at around the age of two. The cause of systemic JIA - the worst form of JIA - is unclear but experts believe it to be an auto-immune condition, like adult rheumatoid arthritis.
The Tender trial, conducted in 20 countries including the UK, involved 112 children with JIA who were either given infusions of tocilizumab or an inactive "dummy" placebo.
More than a third of the children treated with the drug showed a 90% improvement after 12 weeks. Around 85% experienced a 30% improvement in symptoms.
The researchers will continue to monitor the children for five years to assess the long-term effects of treatment.
Results from the trial were presented today at the European League Against Rheumatism (Eular) annual meeting in Rome.
Rheumatology expert Professor Patricia Woo, from Great Ormond Street children's hospital in London, who led one of the UK arms of the trial, said: "This is a major advance for these young people. Children with systemic JIA remain a group with a high unmet medical need, and those at the more severe end of the disease spectrum have significant morbidity (illness) throughout their lives as well as a higher rate of mortality than other types of JIA.
"This condition can seriously disrupt the child's development and the day-to-day life of the family. Without effective treatment up to half of the affected children develop chronic and persistent arthritis and a majority of these children can be left with significant disability."
Children with systemic JIA have high levels of an immune system cell-signalling molecule called IL-6 in their blood and joints.
Tocilizumab works by blocking the IL-6 biological pathway, preventing its signals from getting through.
Neil Betteridge, vice president of Eular and chief executive of Arthritis Care, said: "This robust and new data from Roche is promising and, if proven to be widely successful, will help treat juvenile idiopathic arthritis (JIA), a condition affecting around 12,000 children in the UK under the age of 16.
"Effective treatment of early arthritis can lead to long-term remission for many children, and this can mean decades of improved quality of life - a very different prospect compared to previous generations. Children who benefit from early intervention are more likely to become economically active adults, and less in need of state benefits and financial support from their families."