Importantly, spatial transcriptomic analysis revealed that FGFR4 expression localizes to alveolar fibroblasts and AT2 epithelial cells—key stromal and epithelial compartments implicated in LAM pathophysiology—providing a tissue-level map for where this gain-of-function polymorphism may exert its pathogenic effects. This evidence concerns the gene FGFR4 and lymphangioleiomyomatosis.