As more and more families are beseeching drug companies and insurers to pay for this novel class of treatments, both big and small employers are getting hit with higher drug bills. It may be for a worker’s child with hemophilia whose treatments can cost over $1 million or for an employee receiving immunotherapy for lung cancer. But not every union or corporate employer has an adequate cushion to absorb these prescription bills.

“In the past, we’d think of rare and orphan diseases and an employer would say, oh, I just had bad luck — I had one of these patients,” said Dr. Steve Miller, the chief clinical officer of Cigna, which owns Express Scripts, a pharmacy benefit manager that negotiates with drug companies on behalf of employers to cover prescriptions for 75 million Americans. “Going forward, if we’re successful and have therapies for these things, everyone’s going to have them.”

The Patterson family’s experience also exposes a stunning lack of transparency in drug pricing; many rare-disease drugs are priced based on a patient’s weight, meaning a prescription for an adult costs many times more than one for a child or infant. Pharmaceutical companies often obscure the real cost with initial estimates — provided to the media or Wall Street analysts — that are far less than the eventual real-world cost of the medicines .

In the Pattersons’ case, Strensiq was expected to cost about $285,000 in 2015 according to its manufacturer, Alexion Pharmaceuticals. But here’s the catch: That price was based on the assumption that most patients would be children or infants and would weigh an average of about 50 pounds. In addition, Alexion would not discuss how much it would cost adults. In 2018, Ms. Patterson’s drug bill approached $2 million.

The breathtaking price threw the labor union — the International Brotherhood of Boilermakers, which covers her health care through her husband , Bill — into a crisis.

Four months after she began taking Strensiq, the union’s health plan put payment for the drug on hold to evaluate whether she really needed it.