A new era of expensive drugs has arrived: medicines priced in the millions of dollars a patient. U.S. or European health regulators have approved four new products intended as one-time treatments for rare genetic diseases that carry list prices of at least $2 million a patient.

The most recent one approved in the U.S. set a price record: $3.5 million for CSL Ltd.’s Hemgenix, a treatment for the blood disorder hemophilia B.

The price tags mark a new high for medicines, which drugmakers were once reluctant to charge more than six figures for but whose prices have been heading upward. The companies say the cost reflects the drugs’ potential to help patients in a single dose, but paying for it could challenge patients and health insurers.

Most of the multimillion-dollar treatments are gene therapies, a groundbreaking type of treatment that involves injecting a functional gene into a person to correct a faulty, disease-causing one.

Bluebird’s Skysona gene therapy for a rare neurological disease affecting children costs $3 million, while its Zynteglo for an inherited blood disorder is priced at $2.8 million.

Novartis AG’s Zolgensma gene therapy treating a muscle-wasting condition costs $2.1 million.

Some of the new therapies could produce long-term savings, the companies say,by sparing patients from having to take older treatments repeatedly for the rest of their lives.

McKinsey & Co. estimates that about 30 new gene therapies could be introduced in 2024 alone.