Did the World Just Gain Hundreds of Millions of Alzheimer's Patients?

The piece examines whether Alzheimer’s should be defined by biological changes in the brain, even before memory or thinking problems appear. New blood tests can detect amyloid, a protein associated with the disease, with accuracy approaching PET scans and spinal taps; the FDA cleared its first such test in 2025. Combined with recently approved amyloid-targeting drugs, these tests have fueled hopes that treatment could begin early enough to prevent symptoms. But they also raise a consequential question: whether people with amyloid deposits but normal cognition should be considered to have Alzheimer’s. Donald Kewman, a cognitively healthy man with genetic risk and moderate amyloid accumulation, illustrates the ambiguity: he sees a sense in which he has the disease, while his wife does not.

The debate reflects a shifting definition. Alois Alzheimer identified plaques, tau tangles, and neuron loss in the brain of a woman with severe early-onset dementia in 1906; for decades, the disease’s name chiefly described dementia in younger people. In the 1970s, neurologist Robert Katzman argued that late-onset dementia should also count as Alzheimer’s because it shared features with early-onset cases, despite lacking proof of one common cause. That expansion made a rare diagnosis encompass much of old-age dementia and helped raise its institutional profile. Today’s proposed move from symptoms to biomarkers could expand the label far further. The optimism about treatment is also contested: a large meta-study found amyloid antibodies probably make little to no difference to memory and cognitive decline.