In any complex machine, the lack of a single part can lead to big trouble. That is the problem faced by the 170,000 people globally who have the bleeding disorder known as haemophilia. A genetic mutation (usually inherited) suppresses the production of proteins that make blood coagulate (see page S158). Internal bleeding into the joints causes bone degradation and excruciating pain (S170), and even mild injuries can be life-threatening.

Credit: Jessica Fortner

The standard therapy is frequent infusions with blood-clotting promoters. These treatments are uncomfortable and expensive, so it is welcome news that several longer-lasting clotting factors have been developed (S162). Many people develop an immune resistance to these infused factors, but relief may be on the way in the form of anti-inhibitory pills made from plants (S166). Development of these pills depends on colonies of haemophilic dogs that serve as cooperative test subjects (S172).

Clotting-factor infusions treat symptoms of haemophilia, but gene therapy could provide a cure (S160). Research is also moving ahead on an alternative treatment strategy to remove or disable the body's anticoagulants (S168) rather than adding clotting factors.

The haemophilia community is still haunted by the traumas of blood supplies that were contaminated with HIV and hepatitis C. These experiences have led to reluctance to accept the good news that may soon be on offer, says medical historian Stephen Pemberton (S165).

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