The only cure for painful sickle cell disease today is a bone marrow transplant. But soon there may be a new cure that attacks the disorder at its genetic source.

On Tuesday, advisers to the Food and Drug Administration will review a gene therapy for the inherited blood disorder, which in the United States mostly affects black people. Issues they will consider include whether more research is needed into possible unintended consequences of the treatment.

If approved by the FDA, it would be the first gene therapy on the US market based on CRISPR, the gene editing tool that won its inventors the Nobel Prize in 2020.

The agency is expected to decide on the treatment in early December, before taking up a different sickle cell gene therapy later that month.

Dr Allison King, who cares for children and young adults with sickle cell disease, said she’s enthusiastic about the possibility of new treatments.

“Anything that can help relieve somebody with this condition of the pain and the multiple health complications is amazing,” said King, a professor at Washington University School of Medicine in St Louis. “It’s horribly painful. Some people will say it’s like being stabbed all over.”

The disorder affects hemoglobin, the protein in red blood cells that carries oxygen. A genetic mutation causes the cells to become crescent-shaped, which can block blood flow and cause excruciating pain, organ damage, stroke and other problems.

Millions of people around the world, including about 100,000 in the US, have the disease. It occurs more often among people from places where malaria is or was common, like Africa and India, and is also more common in certain ethnic groups, such as people of African, Middle Eastern and Indian descent. Scientists believe being a carrier of the sickle cell trait helps protect against severe malaria.

Current treatments include medications and blood transfusions. The only permanent solution is a bone marrow transplant, which must come from a closely matched donor without the disease and brings a risk of rejection.

No donor is required for the one-time gene therapy, “exa-cel,” made by Vertex Pharmaceuticals and CRISPR Therapeutics. This new treatment involves permanently changing DNA in a patient’s blood cells.

The goal is to help the body go back to producing a fetal form of hemoglobin — which is naturally present at birth but then switches to an adult form that’s defective in people with sickle cell disease.

When patients undergo the treatment, stem cells are removed from their blood and CRISPR is used to knock out the switching gene. Patients get medicines to kill off other flawed blood-producing cells and then are given back their own altered stem cells.

The treatment has been tested in a relatively small number of patients thus far, the nonprofit Institute for Clinical and Economic Review said in an evidence report.

In a briefing document released Friday before the advisory committee meeting, Vertex said 46 people got the treatment in the pivotal study. Of 30 who had at least 18 months of follow-up, 29 were free of pain crises for at least a year and all 30 avoided being hospitalised for pain crises for that long.

The company called the treatment “transformative” and said it has “a strong safety profile.”