Rare-disease drugmakers are expressing concern that the Republican health care bill—which the Senate could vote on as soon as next week—could allow insurers, including those that offer plans through employers, to cut off reimbursements once an insured person spends $1 million to $2 million on prescription drugs. With expensive rare-disease drugs, that can happen quickly. The Republicans' proposal would give states leeway to allow the return of health coverage caps that were banned under the Affordable Care Act. Treatments for rare diseases brought in $114 billion in worldwide sales last year, according to Evaluate Ltd., and drugmakers are increasingly depending on them to boost revenue. If insurers are permitted to stop paying for them at a certain point, the burden may fall to patients, and ultimately drug companies will pick up the tab for those who cannot afford the cost. In 2016 there were 16 drugs that cost more than $200,000 a year per U.S. patient. The Senate bill does not explicitly remove the ban on lifetime limits, yet it offers a path to restore them. It allows states to cut certain categories from a list of required coverage areas, called essential health benefits, and removing drug coverage from that list would allow insurers to cap their medication benefits.