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Monday, December 19, 2011

Gene therapy for hemophilia


There may be a cure in sight for hemophilia patients.  Researchers led by Amit Nathwani of University College London, along with colleagues from many other institutions have successfully used gene therapy to treat hemophiliacs. This amazing development would not only extend and improve the lives of hemophiliacs, but could be the beginning of a new era of treatments for other genetic diseases.

Hemophilia is a blood-clotting disorder caused by a genetic defect.  Specifically, people with hemophilia B (also called ‘Christmas disease’ after Stephen Christmas, a young sufferer of this condition) are born with a mutation in the gene for the protein factor IX (FIX).  Because this gene is located on the X chromosome, the disease occurs almost exclusively in boys.  To be a hemophiliac, a girl would have to be the misfortunate product of a hemophiliac father and a carrier mother.

Hemophilia patients need regular infusions of the clotting agents they lack in an effort to alleviate symptoms. In contrast, gene therapy, the replacement of faulty or mutated genes with normal versions of those same genes, would permanently cure the patients.  Although a promising idea, little progress has been made due to a number of difficulties, including the problem of providing genetic material in a way that won’t adversely affect other genes or alert the immune system. 

The researchers got around these problems by using a modified adenovirus, to which most people do not exhibit strong immune reactions, as a vector. Six patients with hemophilia B, each of whom had required supplementation with FIX protein between one and three times per week, were infused with the FIX-adenoviruses.  After treatment, their FIX levels remained stable at between 2 and 12% of normal (all had been below 1% prior to the treatment) for up to 15 months.  Some of the patients did require extra FIX protein, but at a much lower rate than before the treatment.

This was obviously an extremely small study.  Much more work must be done before gene therapy can be approved for general usage.  For one thing, the optimal dosage for delivering FIX must be determined. Also, it’s too early to tell how long the treatment will last, or whether it will produce any unforeseen consequences.  For now, the doctors and patients alike have reason to celebrate.