Autosomal dominant Alzheimer’s disease (ADAD) is a genetically inherited form of Alzheimer’s disease that accounts for only about 1% of Alzheimer’s disease cases. However, because individuals with the gene mutations are extremely likely to develop Alzheimer’s disease at an early age, and because the mutation is highly heritable, ADAD is widely studied by Alzheimer’s disease researchers.

A new study by WashU Medicine researchers and collaborators, published in The Lancet Neurology, identified variants in three other genes that seem to change how Alzheimer’s disease presents in people with ADAD mutations. Pinpointing these and other genetic factors that affect Alzheimer’s disease development and progression may allow investigators to provide more effective genetic counseling for families, design clinical trials and develop new treatments to prevent or slow Alzheimer’s disease in the larger population.

Previous studies had already identified three key genes—amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2)—that are associated with ADAD, as well as 279 variants in those genes that lead to Alzheimer’s disease. What remains unclear, however, is what leads to differences in disease onset and progression among individuals who have a disease-causing variant. For instance, even if a person carries an APP, PSEN1 or PSEN2 mutation and is therefore very likely to develop early-onset Alzheimer’s, there is variability in when symptoms of cognitive decline might begin, even among individuals who have the same disease-causing mutation.