Key points from article :
Haemophilia prevents production of a protein needed to stop bleeding.
Even the impact of walking can lead to bleeding in joints.
Sufferers typically need injections of factor VIII every other day for life.
Trial resulted in 11 of 13 participants producing near-normal levels of the protein.
Gene therapies are very expensive but factor VIII injections cost £100,000 per year.
Haemophilia effects 2,000 people in the UK.
The study was published in the New England Journal of Medicine.
COMMENT: cost of gene therapies will reduce as they become more common
