PARIS • Scientists have used gene therapy to relieve the symptoms of a teenager suffering from sickle cell disease, an inherited illness caused by a gene mutation that results in red blood cells losing their usual doughnut-like appearance and taking on a sickle or crescent moon shape.

Sufferers of the disease - around five million worldwide - often have anaemia and get tired easily, run a higher risk of infections and stroke, and experience bouts of severe body pain. Many need chronic blood transfusions.

A team from the AP-HP university hospital group in Paris, the Imagine Institute of Genetic Diseases and gene therapy firm Bluebird Bio said they managed to get the teenager off transfusions.

He was the first person to be treated, in Paris in October 2014, for sickle cell disease in a clinical trial with gene therapy.

The team collected so-called haematopoietic stem cells, which give rise to red blood cells, from the bone marrow of the boy, then aged 13.

The immature cells were treated with a therapeutic gene, carried in a deactivated virus, which recoded their DNA to correct blood cell production.

The treated cells were injected into the boy's body.

The study, published in the New England Journal Of Medicine, reported on the child's health 15 months after treatment.

"He is well, he no longer needs monthly (blood) transfusions, anti-pain medication or hospitalisation," said study leader Marina Cavazzana.

The disease is common in Africa, where up to 40 per cent of a country's population can carry the mutated gene, though most never get sick.

AGENCE FRANCE-PRESSE