A Cambridge biotech startup that’s working on treatments for serious and rare diseases will pay a California drug maker $150 million in licensing fees for worldwide rights to a medicine expected to win approval this year.

Akcea Therapeutics, an affiliate of Ionis Pharmaceuticals Inc., of Carlsbad, Calif., will pay the sum upfront to Ionis for the rights to a drug to treat hereditary TTR amyloidosis, a systemic, progressive, and fatal disease. That drug, inotersen, is expected to win approval from the Food and Drug Administration and European regulators in mid-2018.

As part of the deal, Akcea, also will acquire a second drug Ionis developed for a form of TTR amyloidosis that is not inherited, according to Paula Soteropoulos, Akcea’s chief executive. That drug has yet to enter clinical trials.

Ionis focuses on research and development of drugs and forms partnerships with other companies to bring the products to market. Ionis founded Akcea three years ago hoping the Cambridge startup would market four other drugs in the Ionis pipeline. (Akcea went public in July, but Ionis still owns about 75 percent of the company, said Soteropoulos.)

One of those four medicines, volanesorsen, is expected to win approval from the FDA and regulators in Canada and Europe later this year, said Soteropoulos. It would treat an extremely rare metabolic disorder called Familial Chylomicronemia Syndrome.

People with FCS are unable to metabolize triglycerides properly, a gravely serious problem.

If the latest deal between Ionis and Akcea meets certain goals, the transaction could be worth up to $1.7 billion to Ionis, plus profit-sharing payments

Jonathan Saltzman can be reached at jsaltzman@globe.com