The complex biological mechanisms underlying human brain aging remain incompletely understood. To investigate this, we utilized multimodal magnetic resonance imaging and artificial intelligence (AI) to examine the genetic heterogeneity of the brain age gap (BAG) derived from gray matter volume (GM-BAG), white matter tract (WM-BAG), and functional connectivity (FC-BAG). Sixteen significant genomic loci were identified, with GM-BAG loci showing abundant associations with neurodegenerative and neuropsychiatric traits, WM-BAG for cancer and Alzheimer's disease (AD), and FC-BAG for only insomnia. The gene-drug-disease network further corroborated these associations by highlighting genes linked to GM-BAG for the treatment of neurodegenerative and neuropsychiatric disorders, and WM-BAG genes for cancer therapy. GM-BAG showed the highest enrichment of heritability in conserved regions, while in WM-BAG, the 5' untranslated regions exhibited the highest heritability enrichment; oligodendrocytes and astrocytes showed significant heritability enrichment in WM and FC-BAG, respectively. Notably, Mendelian randomization identified risk causal effects of triglyceride-to-lipid ratio in VLDL and type 2 diabetes on GM-BAG, and AD on WM-BAG. These findings suggest that interventions targeting these factors and diseases may ameliorate human brain health. Overall, our results provide valuable insights into the genetic heterogeneity of human brain aging, with potential implications for lifestyle and therapeutic interventions.

Normal and pathologic neurobiological processes influence brain morphology in coordinated ways that give rise to structural covariance patterns across brain regions and individuals. We present a mega-analysis of structural covariance with magnetic resonance imaging of 50,699 healthy and diseased individuals (12 studies, 130 sites, and 12 countries) over their lifespan (ages 5 through 97). Patterns of structural covariance (PSC) were highly heritable (0.05< h2 <0.78) and significantly associated with 1610 independent significant variants after Bonferroni correction (10.3 > -log10[p-value] > 8.8): 1245 previously unreported, and 69% of them independently replicated (-log10[p-value] = 4.5). Associations revealed an imaging phenotypic landscape between 2003 PSCs and 49 clinical and cognitive traits at multiple scales. We constructed machine learning-derived individualized imaging signatures for various disease diagnoses using PSC features at multiple scales, suggesting that disease effects on the brain were better manifested in a multi-scale continuum than on any single scale. Experimental results were integrated into the Multi-scale Structural Imaging Covariance (MuSIC) atlas and made publicly accessible through the BRIDGEPORT web portal (https://www.cbica.upenn.edu/bridgeport/). Our results reveal strong associations between brain structural covariance, genetics, and clinical phenotypes, supporting that PSCs can serve as an endophenotypic anatomic dictionary in future research.