The cell has an unusual shape

The condition, caused by a defect in a blood component called haemoglobin, can be extremely painful, and raises the risk of pneumonia and strokes.

Current drugs work by boosting haemoglobin production, but not all patients respond.

A team from the University of Illinois in Chicago has found another drug, decitabine, may provide an alternative.

This is potentially an exciting addition to the therapies available to treat sickle cell disease. Dr Mark Layton

Sickle cell is an inherited disorder that largely affects Afro-Caribbean and Asian patients.

It causes patients' bone marrow to produce red blood cells with defective haemoglobin.

These cells are a malformed sickle-shape, and cannot easily pass through small blood vessels.

This can lead to damage to the lining of the blood vessels, increase blood clotting and damage to the organs.

Children unaffected

Children, however, are immune to the effects of sickle cell disease because they have high levels of foetal haemoglobin still circulating in their bloodstream. This form of haemoglobin is not affected.

As the levels of foetal haemoglobin drop, then they begin to develop the disease.

The standard treatment for sickle cell is a drug called hydroxyurea. This re-stimulates the production of foetal haemoglobin by turning on the gene that is usually switched off in adulthood.

However, some people do not respond to the drug at all.

Bone marrow transplants are available, but usually only to young people with severe complications.

And blood transfusions can be used to dilute sickle cells - but no nothing to tackle the problem at source.

The Chicago team decided to investigate whether decitabine could provide an alternative for those patients who do not respond to hydroxyurea.

Their study focused on eight sickle cell patients with significant complications who were either resistant to or intolerant of hydroxyurea.

Each was given a relatively low dose of decitabine one to three times per week in two six-week cycles, with a two-week interval between cycles.

The researchers found that haemoglobin levels rose, and other signs of the disease improved.

Different action

Lead researcher Dr Yogen Saunthararajah said decitabine probably stimulated haemoglobin in a way different to hydroxyurea.

He said: "These results are exciting as patients who do not respond to hydroxyurea need alternative therapies that can increase the quality and quantity of their lives.

"Further studies with decitabine should be performed to demonstrate if this agent, administered over prolonged periods of time, can improve the quality of life for patients with sickle cell disease."

Dr Mark Layton, a medical advisor to the Sickle Cell Society, told BBC News Online: "This is potentially an exciting addition to the therapies available to treat sickle cell disease.

"However, issues about the long term efficacy and toxicity of treatment with decitabine have yet to be resolved, and we do need a longer term study."

He also said that unlike hydroxyurea, which is available in pill form, decitabine was administered by an injection under the skin in a similar way to the jabs given to people with diabetes.

The research is published in the journal Blood.