After years of effort, scientists and families of young patients with the genetic condition Niemann-Pick Type C are in a position to which any rare-disease community aspires: the prospect of not one, not two, but three companies launching clinical trials to develop therapies.

But the flurry of commercial interest has sparked an urgent debate. Can the community support more than one trial at the same time?

The pharmaceutical companies need to enroll enough patients to demonstrate results. The pool of eligible patients with a rare disease like NPC is small, though. Doctors say there aren’t yet reliable counts of diagnosed cases, but current estimates put the number at around 500 world-wide.

As companies compete for participants, some scientists and families are worried that they may siphon patients away from each other, and the result will be that no trial has the heft to get a drug approved.

“This is a critical juncture for our community,” said Nadine Hill, executive director of the National Niemann-Pick Disease Foundation, whose annual conference this month in Chicago became the forum where many of the fears got aired. “To lose out on having an approved treatment is our worst-case scenario.”

The growing interest of drug companies in rare diseases is the result of years of successful and growing patient activism. Patient communities raise money, support research and sometimes reach out personally to drug companies, which also recognize that rare-disease drugs can command high prices. The Food and Drug Administration said that 17 of the 41 new drugs it approved in 2014 were for rare diseases.

But even with more common conditions like cancer, it isn’t always easy to get patients onto trials. Patients worry they will get a placebo, and trials can require travel and time off work or school. Trials also require patients with very specific characteristics such as a particular age range or stage of disease, which limits the pool of potential participants—a problem exacerbated in rare diseases.

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