Alzheimer’s researchers got a huge boost last week with the publication of a study showing that a rare genetic mutation prevents the buildup of beta amyloid in the brain.

Alzheimer’s experts believe this finding is the most significant development in 20 years since it supports the hypothesis that excessive levels of beta amyloid in the brain are responsible for this form of dementia, the New York Times reported. The finding is also a boon to pharmaceutical companies that have been developing anti-amyloid drugs.

Drugmakers such as Genentech and Eli Lilly told the Times that they were encouraged by the findings because even though anti-amyloid drugs have so far been unsuccessful, the focus on reducing amyloid levels is “a logical path for the development of effective therapies that may slow disease progression,” said Richard Mohs, Ph.D., leader of neuroscience early clinical development at Eli Lilly.

The study, which was conducted by investigators at the Icelandic company DeCode Genetics, was published last week in the journal Nature.