The U.S. health regulator has approved Vertex Pharmaceuticals and CRISPR Therapeutics' gene therapy to treat a rare blood disorder requiring regular blood transfusions, in patients 12 years and older, Vertex said on Tuesday.

The decision earns the therapy, branded as Casgevy, the second U.S. approval after it was greenlighted in December for sickle cell disease, another inherited blood disorder.

The approval by the Food and Drug Administration comes more than two months ahead of its expected action date of March 30.

Casgevy, which requires administration through authorized treatment centers with experience in stem cell transplantation, would be made available early this year at a list price of $2.2 million in the United States for both the approved indications, Vertex said in an email response.

Oppenheimer analyst Hartaj Singh said he expects a "slow and steady launch" for the therapy and estimated combined peak sales of about $400 million.

"We think Casgevy's profile will do fine for patients naive to therapy," Singh said.

Casgevy becomes the first treatment based on the Nobel Prize-winning CRISPR gene editing technology to secure approval for transfusion-dependent beta thalassemia (TDT) in the United States.

CRISPR, discovered by Jennifer Doudna and CRISPR Therapeutics co-founder Emmanuelle Charpentier, uses molecular "scissors" to trim faulty parts of genes that can then be disabled or replaced with new strands of normal DNA.

Rival bluebird bio's Zynteglo, in 2022, became the first cell-based gene therapy to secure the FDA's nod to treat adult and pediatric patients with TDT and was priced at a record $2.8 million.

TDT, or Cooley's anemia, the more severe form of the disorder, causes children to develop life-threatening anemia which requires blood transfusions every two to five weeks.

More than 100,000 people are estimated to have transfusion-dependent thalassemia globally with at least 1,200 people with the disorder in the United States, according to data from Boston Children's hospital.