The Food and Drug Administration on Friday approved Pfizer’s treatment for a rare genetic bleeding disorder, making it the company’s first-ever gene therapy to win clearance in the U.S.

The agency greenlit the drug, which will be marketed as Beqvez, for adults with moderate to severe hemophilia B who meet certain requirements.

The treatment will be available by prescription to eligible patients this quarter, a Pfizer spokesperson told CNBC. It has a hefty $3.5 million price tag, before insurance and other rebates, the spokesperson added, making it by far one of the most expensive drugs in the U.S.

More than 7,000 people in the U.S. are living with the debilitating condition, which predominantly affects men, according to an advocacy group. The condition is caused by insufficient levels of a certain protein that helps blood form clots to stop bleeding and seal wounds. Without that protein, called factor IX, patients with hemophilia B bruise easily and bleed more frequently and for longer periods of time.