Novel COL4A3–COL4A5 variants and digenic inheritance in pediatric Alport syndrome from Southwestern China

Alport syndrome is a hereditary glomerular disease driven by pathogenic variants in COL4A3-COL4A5 that compromise the α3-α4-α5 type IV collagen scaffold, manifesting as persistent hematuria, proteinuria, and ultimately end-stage renal disease. Its pronounced phenotypic variability, low sensitivity of renal biopsy, and limited response to ACE inhibitors complicate accurate diagnosis and therapy. In a cohort of 40 pedigrees from southwest China, we discovered 21 novel COL4A3-COL4A5 mutations. Notably, two families carried rare digenic COL4A4/COL4A5 variants, providing strong evidence for dual-locus pathogenicity. Immunofluorescence of five mutation-positive patients revealed allele-specific depletion of α3 and α5 chains in the glomerular basement membrane, with frameshift and splice-site mutations eliciting more severe collagen loss than missense. Complementary AlphaFold modeling predicted that digenic variants induce greater destabilization of Gly-X-Y triple helices domain than monogenic lesions. Over three years, ACEI therapy achieved only sporadic partial remissions, underscoring the need for precision-guided treatment strategies. This study not only expands the genetic spectrum of Alport syndrome in China's ethnic minority populations but also elucidates the mechanistic impact of digenic inheritance.