To see if there’s a connection between the price of a gene therapy and the estimated number of patients it will treat per year, we decided to plot those figures for the approved gene therapies in the U.S. and Europe and one that’s pending approval in the U.S.

Herman Sanchez, managing partner at life science consulting firm Trinity Partners, says there is a correlation between the patient population and price of the therapy: the fewer eligible patients, the more expensive it is. As you can see, prices range from $373,000 to $1 million, while the number of patients per year is as low as just a few to 7,500.

“The smallest diseases have more pricing power in the marketplace,” he says. “That’s usually due to the fact that payers don’t have to deal with a lot of patients.”

So far, Yescarta is the outlier. It could help as many as 7,500 people, according to Gilead, the biotech giant that acquired the drug’s maker, Kite Pharma in August. Compare that with the tiny eligible populations for the two gene therapies approved in Europe, Glybera and Strimvelis. Meanwhile, in the U.S., Novartis says about 300 patients a year will be eligible for its gene therapy Kymriah, which treats a type of childhood leukemia. With more patients, Gilead was able to set a lower price but might see higher overall revenues in the end.

Though Yescarta’s price still prompted outcries from patient advocates, it bodes well for gene therapies in the pipeline for diseases with more patients, like hemophilia and sickle-cell, which affect about 20,000 people and 100,000 in the U.S., respectively.