In recent decades, advances in medicine have changed the way we think about our health. Chronic diseases like obesity, heart disease, and diabetes can be prevented or reversed. Cancer treatment has become targeted and personalized. Gene editing will allow us to eradicate many inherited disorders. But there is one class of conditions that continues to elude researchers and cause tremendous suffering: neurodegenerative disease.

More than six million Americans live with Alzheimer’s disease; by 2050, this number is projected to reach thirteen million. An additional one in ten people over the age of sixty-five have dementia, while 22 percent of older adults live with some form of cognitive impairment. And it isn’t just the elderly who are afflicted; diagnosis rates are rising in younger adults, with women at a higher risk than men. For many―especially those with a genetic predisposition―this fate has seemed inevitable. Until now.