The U.S. Food and Drug Administration can approve new personalized treatments for rare and deadly genetic diseases based on data from a handful of patients, two of the agency's top officials said on Wednesday.

FDA Commissioner Marty Makary and Chief Medical and Scientific Officer Vinay Prasad said in an essay published in the New England Journal of Medicine that for certain conditions, companies could rely on appropriately designed studies with small sample sizes rather than randomized trials. They will rely on biological plausibility and clinical improvements in those early patients.

"Current regulations are onerous and unnecessarily demanding," Makary and Prasad wrote. "For patients and families, there is no time to wait."

The new "plausible-mechanism" pathway would allow the agency to grant marketing authorization after manufacturers demonstrate success with several consecutive patients.

Companies that receive these approvals will be required to collect real-world evidence to confirm efficacy continues and to look for safety issues that might arise.

The new approach will prioritize treatments for rare diseases that are fatal or cause severe childhood disability. Common diseases with unmet medical needs may also qualify.

While makers of cell and gene therapies are likely to be significant beneficiaries of the new approval process, Makary and Prasad said that other types of treatments could also receive licensure this way.

"The FDA will work as a partner and guide in ushering these therapies to market," the officials wrote.