Alzheimer's disease, the most common form of dementia, has beaten back potential treatments for decades. Past research suggested it was a complicated, multifactorial disease in which a patchwork of biological and lifestyle factors combined to increase or decrease risk.

But a new study published in January in the journal Nature suggests the risk of developing the disease is determined largely by one key gene, called apolipoprotein E (APOE). Lifestyle and environmental factors can dial the risk up or down modestly in people with susceptible gene variants, but those who have protective versions of the APOE gene are extremely unlikely to develop Alzheimer's. And a staggering 99% of the population carries at least one disease-fueling version of the gene.

The findings raise the possibility that gene therapy targeting APOE could dramatically reduce the risk of Alzheimer's for a large swath of people who are at risk of developing the disease, thus paving the way for one of the first widely used gene therapies, experts told Live Science.