Doctors hope the one-time treatment, which involves permanently altering DNA in blood cells may treat and possibly cure sickle-cell disease and beta thalassemia.

Partial results were presented on Saturday at an American Society of Hematology conference and some were published by the New England Journal of Medicine.

Doctors described 10 patients who are at least several months removed from their treatment. All no longer need regular blood transfusions and are free from the pain that plagued their lives before.

Victoria Gray, the first patient in the sickle-cell study, had long suffered severe pain bouts that often sent her to the hospital.

"I had aching pains, sharp pains, burning pains, you name it. That's all I've known my entire life," Gray, 35, said.

"I was hurting everywhere my blood flowed."

Since her treatment a year ago, Gray has weaned herself from pain medications she depended on to manage her symptoms.

"It's something I prayed for my whole life," she said.

"I pray everyone has the same results I did."

Sickle cell affects millions, and is particularly prevalent among black people. Beta thalassemia strikes about one in 100,000 people.

The only cure currently is a bone marrow transplant from a closely matched donor.

Both diseases involve mutations in a gene for haemoglobin, the substance in red blood cells that carries oxygen throughout the body.

Saturday's results were on the first 10 patients, seven with beta thalassemia and three with sickle cell. The two studies in Europe and the United States are ongoing and will enrol 45 patients each.

"The preliminary results are extremely encouraging," Dr. Haydar Frangoul of the Sarah Cannon Research Institute in Nashville said.

Australian Associated Press