How a tailored ALS drug could help broaden rare disease therapies

Jared Whitlock (Endpoints News)

June 18, 2025

In 2020, Jaci Hermstad died at age 26 from a rare and aggressive form of ALS. But her story didn’t end there.

A drug that was created just for her, called Jacifusen, has since been given to others with mutations in the FUS gene, what’s known as FUS-ALS. The results in the first 12 patients, published in May in The Lancet, suggest the therapy slowed disease progression in some cases in what’s considered an untreatable condition. One patient even recovered for a period.

The company that hatched the drug, Ionis Pharmaceuticals, is now sponsoring a late-stage trial that will determine whether the therapy is effective and safe enough to seek approval. Several thousand patients are afflicted by FUS-ALS.

Custom treatments, known as “n-of-1” therapies, were once seen as an end in themselves. But now they’re a launchpad to reach more patients. Beyond Ionis, the model is being pursued by various organizations, from the company La Jolla Labs to Boston Children’s Hospital to the n-Lorem Foundation.

The concept is becoming more popular, especially as new patients are discovered through genetic testing or found to share molecular mechanisms, even if they have different diseases.

Individualized therapies are often funded by family charities and academic groups. But in some cases, companies see a business model in going broader: Starting with individual patients can generate early data and smooth the path to larger markets. The approach can raise ethical questions, and for regulators, it can be tough to decide how much evidence is needed before broadening the use of a medicine.

Jacifusen was originally conceived as a one-off endeavor by a doctor who rebooted the Ionis therapy. But it could ultimately serve as a template for how personalized drugs can reach many. The possibility brings comfort to Jaci’s mother, who said that Jaci believed everything she endured would help others.

“Though our hearts remain broken, the promise of helping others brings us peace,” Lori Hermstad, Jaci’s mother, said in an interview with Endpoints News.

Image credit: Lori Hermstad

We have the technology

Jacifusen is built on antisense oligonucleotides. These molecular tools precisely target disease-causing proteins and represent the most widely-used approach in custom drug development, due to their established safety profile and manufacturing scalability.

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