Hereditary spastic ataxia (HSA) is a rare disease only reported in patients from Newfoundland, Canada. It isn’t deadly, but it can be debilitating — causing problems with speech, swallowing, and muscle coordination, often leaving patients wheelchair-bound by age 50 — and it gets passed down from parent to child in a dominant fashion.

But now researchers in Montreal say they've discovered the genetic root of HSA in a reanalysis of the DNA of three large Newfoundland families, who are ancestrally related and had the disease. In the study, published in the American Journal of Human Genetics, the scientists say the mutation causing the disease can be found in the gene VAMP1, which encodes the synaptobrevin protein.

"Not only was the mutation present in all patients and absent from all population controls, but also, synaptobrevin is a key player in neurotransmitter release, which made sense at the functional level as well," lead researcher Cynthia Bourassa, of the University of Montreal, said in a statement. In other words, messing with synaptobrevin may affect the nervous system in a way that causes the symptoms of HSA.

"The discovery will benefit the families affected with this extremely debilitating disorder," another University of Montreal researcher, Dr. Guy Rouleau, said in a statement. "A genetic diagnostic test can be developed, and genetic counseling can be provided to family members who are at risk of developing the disease or having children with the condition."