Fault Lines in the Genome: Somatic DNA Mutations in Aging and Neurodegeneration.

The human genome is both fragile and resilient: prone to alteration yet protected by extensive repair mechanisms. With age, individuals accumulate genetic damage from environmental factors and cell-intrinsic processes, with effects ranging from benign nucleotide shifts to disease-driving mutations. Such alterations to the genetic code outside the germline are described as somatic mutations and display striking heterogeneity across cell types. Recently, somatic mutations have emerged as a hallmark feature of aging in the body's longest-lived tissue: the central nervous system (CNS). The distinctively long lifespan, high metabolism, electrochemical activity, and unique epigenome of CNS cells may render them especially vulnerable to mutational accumulation. The CNS therefore provides a model for understanding how somatic mutations drive cellular dysfunction beyond an established role in cancer. Here, we review the somatic mutations that arise in the brain across lifespan, the mechanisms that lead to their formation, and their potential contributions to aging and age-related disease.