Integrative Genomic and Functional Investigation of the Multi‐Layered Genetic Architecture Between Anorexia Nervosa and Bone Loss

OBJECTIVE: Bone loss is a severe and often irreversible complication of anorexia nervosa (AN), yet the genetic mechanisms underlying this comorbidity remain underexplored. This study focuses on constructing a comprehensive genetic architecture between AN and estimated calcaneal bone mineral density (eBMD). METHOD: We applied an integrative framework incorporating genetic correlation, pleiotropic association, and causal inference across single-variant, multi-variant, and gene expression levels. Functional validation was conducted in vitro to investigate the biological role of the key candidate gene. RESULTS: Local genetic correlation analysis identified significant signals at 8p21.2 and 10q26.3, despite the lack of significant global correlation. Mendelian randomization analysis pointed to a suggestive negative causal effect of genetically predisposed AN on eBMD. Extensive pleiotropic signals were detected, particularly at 3p21.31 and 10q26.3, loci enriched with genes associated with both traits. Notably, we identified a novel pleiotropic signal near NCAM1 at 11q23.2, which was supported by multi-layered genetic evidence and confirmed through in vitro functional experiments. NCAM1, a well-established neural-associated gene, promoted osteoclastic differentiation and bone resorption when overexpressed in osteoclast precursor cells, indicating that NCAM1 possesses distinct functional roles in both neural and skeletal tissues. DISCUSSION: This study constructs a comprehensive genetic architecture underlying AN and eBMD and highlights NCAM1 as a key pleiotropic gene.