The genetic landscape of Alzheimer disease.

Alzheimer disease (AD), a progressive and neurodegenerative disease, is the most common form of dementia with high incidence in elderly people. Neuropathologically the disease is defined by the combined presence of extracellular amyloid-beta (Aβ) plaques and intracellular neurofibrillary tangles of phosphorylated tau protein. Genetically, the first clues were provided by genetic linkage studies that led to the identification of APP, PSEN1, and PSEN2 mutations as the main causes of autosomal-dominant early-onset AD. Another important hallmark was the identification of the APOE ɛ4 allele as a risk factor for late-onset AD. Over the last 20 years the development and implementation of new genetic and genomic technologies have allowed the identification of other genetic players in this disease. Genome-wide association studies identified more than 20 loci with common variability having small contributions to the susceptibility of AD. The majority of the genes mapped in these loci are known to be involved in specific biologic pathways: cholesterol metabolism, immune response, and endocytosis. More recently, the application of next-generation sequencing (mainly whole-exome sequencing) has begun to reveal the contribution of rarer variants with medium effects on risk for AD. This area of research has come a long way with many and important results allowing a better understanding of the disease. More efforts are still needed, however, to fully understand the etiology of this disease in order to establish reliable individual predictive models and put us closer to the development of a curative, preventive, or modulator drug.