This study shows that a variant of TREM2 , which encodes a protein that suppresses inflammation, causes susceptibility to Alzheimer's disease. Although the variant is rare, its effect on the risk of disease is similar to that of the ε4 allele of apolipoprotein E. Alzheimer's disease, the most common form of dementia in the elderly, is a neurodegenerative disorder that is characterized by a slow but progressive loss of cognitive function. Extracellular amyloid plaques, intracellular neurofibrillary tangles, and loss of neurons and synapses resulting in brain atrophy are the main pathological hallmarks of Alzheimer's disease. 1 Disease onset is usually after the age of 70 years, although the prevalence increases exponentially with age after the age of 65 years and exceeds 25% in those over the age of 90 years. 2 The vast majority of variants in the sequence of the genome that have been shown . . .