Region- and Cell-specific Aneuploidy in Brain Aging and Neurodegeneration

Variations in genomic DNA content, or aneuploidy, are a well-recognized feature of normal human brain development. Whether changes in the levels of aneuploidy are a factor in Alzheimer's disease (AD) is less clear, as the data reported to date vary substantially in the levels of aneuploidy detected (0.7-11.5%), possibly due to methodological limitations, but also influenced by individual, regional and cellular heterogeneity as well as variations in cell subtypes. These issues have not been adequately addressed to date. While it is known that the DNA damage response increases with age, the limited human studies investigating aneuploidy in normal aging also show variable results, potentially due to susceptibility to age-related neurodegenerative processes. Neuronal aneuploidy has recently been reported in multiple brain regions in Lewy body disease, but similar genomic changes are not a feature of all synucleinopathies and aneuploidy does not appear to be related to alpha-synuclein aggregation. Rather, aneuploidy was associated with Alzheimer's pathology in the hippocampus and anterior cingulate cortex and neuronal degeneration in the substantia nigra. The association between Alzheimer's pathology and aneuploidy in regions with limited neurodegeneration is supported by a growing body of in vitro and in vivo data on aneuploidy and beta-amyloid and tau abnormalities. Large-scale studies using high-resolution techniques alongside other sensitive and specific methodologies are now required to assess the true extent of cell- and region-specific aneuploidy in aging and neurodegeneration, and to determine any associations with pathologies.