Deciphering the complexity: a case of kidney failure with co-inheritance of COL4A5 and APOE variants.

BACKGROUND: Alport syndrome (AS) is the most common inherited glomerular disease among patients with chronic kidney disease. With exome sequencing now widely used in clinical practice, pathogenic variants in Alport-related genes (COL4A3/COL4A4/COL4A5) are increasingly identified in patients with diverse phenotypes, including proteinuria‑predominant disease and kidney failure of unknown etiology. Diagnostic complexity further increases when COL4A3/COL4A4/COL4A5 variants are co‑inherited with pathogenic variants associated with other genetic kidney disorders.

CASE PRESENTATION: We reported a 31‑year‑old male presenting with kidney failure, significant proteinuria, familial hematuria and hyperlipidemia. Whole‑exome sequencing (WES) identified two pathogenic variants: a hemizygous COL4A5 variant (c.2105G > A; p.Gly702Asp) and a heterozygous APOE Kyoto variant (c.127C > T; p.Arg43Cys). Given the potential dual diagnosis of AS and lipoprotein glomerulopathy (LPG), a kidney biopsy was performed. Histologic examination revealed uneven thickness of the glomerular basement membrane consistent with the diagnosis of AS, but no LPG-related lesions were observed, indicating incomplete penetrance of APOE Kyoto variant. Cascade family screening detected APOE Kyoto variant in the patient's father and elder sister, both of whom lacked proteinuria until follow-up period.

CONCLUSION: This case highlights the complementary role of kidney biopsy alongside WES in AS with complex genetic mechanisms. It also illustrates the incomplete penetrance of APOE Kyoto, common among Chinese carriers.