A small study which shows that symptoms improved significantly in adults with the bleeding disorder haemophilia B following a single treatment with gene therapy has caused a stir among the scientific community.

A single treatment with gene therapy developed by researchers at St Jude Children's Research Hospital in Memphis, USA has been demonstrated to be safe in a clinical trial conducted at University College London. The findings of the six-person study mark the first proof that gene therapy can reduce disabling, painful bleeding episodes in patients with the inherited blood disorder; the esults were published by the New England Journal of Medicine and presented at the American Society of Hematology meeting in San Diego.

Four participants stopped receiving protein injections to prevent bleeding episodes after undergoing the therapy and have not suffered spontaneous bleeding. Several have also participated in marathons and other activities that would have been difficult prior to gene therapy.

The study used adeno-associated virus (AAV) 8 as the vector to deliver the Factor IX gene along with additional genetic material into the patient's liver. AAV8 belongs to a family of viruses that target liver cells but do not cause disease in humans or integrate into human DNA. Participants in the study received no immune-suppressing drugs prior to gene therapy.

Lead author Amit Nathwani of the UCL Cancer Institute said that "this is a potentially life-changing treatment for patients with this disease and an important milestone for the field of gene therapy". He added that it could have ramifications for the treatment of haemophilia A, other protein and liver disorders and chronic diseases such as cystic fibrosis.

The study's senior author, Andrew Davidoff of the St Jude Department of Surgery, noted that even modest increases that raise Factor IX production to more than 1% of normal levels have the potential to dramatically affect a patient's quality of life and reduce bleeding episodes. However, "the first patient has been followed for the longest time, and his levels have remained at 2% for more than 18 months".

He added that "these results are highly encouraging and support continued research". More patients are scheduled to be enrolled in future trials scheduled to begin later this year.