From renal biopsy to genetic diagnosis: EYA1 mutation in branchio-oto-renal syndrome with renal insufficiency

Branchio-Oto-Renal (BOR) syndrome is a multisystemic autosomal dominant disorder characterized by pre-auricular pits, hearing loss, branchial fistulae, and renal urinary tract malformations. Although renal involvement is common in BOR syndrome, studies on its renal pathological features remain relatively scarce. An 18-year-old male presented with proteinuria, renal insufficiency, hearing loss, preauricular fistulas, and branchial fistulas. Imaging revealed small kidneys, and renal biopsy showed mild mesangial proliferative glomerular lesions, mild chronic tubulointerstitial injury with acute exacerbation. Electron microscopy demonstrated focal thinning of the glomerular basement membrane and segmental foot process effacement. Genetic testing identified a pathogenic variant (EYA1 c.1081 C > T p.Arg361*). The clinical manifestations and severity of BOR syndrome are highly variable, making it prone to misdiagnosis or missed diagnosis. Genetic testing identified the pathogenic EYA1 variant in this case, and the pathological feature of focal thinning of the glomerular basement membrane was reported for the first time. This expanded the understanding of renal damage associated with this disease. For patients with unexplained renal insufficiency, detailed physical examination combined with genetic testing is necessary to improve the early diagnosis rate of BOR syndrome.