“In these villages, you have roads that are bad — doctors aren’t available,” said Dr. Sampaio, who visited last year. “We cannot do studies in populations that do not have access to minimal standards of care. So this might be a Catch-22 type situation. Engaging them in research raises ethical concerns, but if they were enrolled, their access to care would improve.” For now, Dr. Sampaio said, Enroll-HD plans to work only with people who live in Barranquilla or who have the wherewithal to get there.

Dr. Muñoz-Sanjuan of Factor H said he was optimistic that, with effort, conditions could be improved enough to allow people like Mari and Julieta to someday join a clinical trial.

“The obstacle on the coast has been fragmented efforts without a holistic approach,” he said. “People want help from a clinical and social perspective; we need access to people to develop better therapies. These two things have to be connected.”

Maripaz

Gepsy Ariza, 34, does not know how her family is related to others around the region, just that they are a Huntington’s family. A pensive young woman, she, too, recounts the experience of caring for an ailing mother, of Dr. Daza and his medicines, and of giving her blood to some neurology students, only to be told later that the samples had been lost.

In the dusty beach town where she lives, a short drive from Barranquilla yet a universe away from its comforts, Ms. Ariza helps look after her sister, Maripaz Ariza. At only 30, Maripaz has hands that fan and twist like a Balinese dancer’s, a wavering voice, and a stiff, awkward gait.