ADrosophilamodel to screen Alport syndromeCOL4A5variants for their functional pathogenicity

Abstract

ABSTRACTAlport syndrome is a hereditary chronic kidney disease, attributed to rare pathogenic variants in either of three collagen genes (COL4A3/4/5) with most localized inCOL4A5. Trimeric type IV Collagen α3α4α5 is essential for the glomerular basement membrane that forms the kidney filtration barrier. A means to functionally assess the many candidate variants and determine pathogenicity is urgently needed. We usedDrosophila, an established model for kidney disease, and identifyCol4a1as the functional homolog of humanCOL4A5in the fly nephrocyte (equivalent of human podocyte). Fly nephrocytes deficient forCol4a1showed an irregular and thickened basement membrane and significantly reduced nephrocyte filtration function. This phenotype was restored by expressing human reference (wildtype)COL4A5, but not byCOL4A5carrying any of three established pathogenic patient-derived variants. We then screened seven additional patientCOL4A5variants; their ClinVar classification was either likely pathogenic or of uncertain significance. The findings support pathogenicity for four of these variants; the three others were found benign. Thus, demonstrating the effectiveness of thisDrosophilain vivo kidney platform in providing the urgently needed variant-level functional validation.SUMMARY STATEMENTDrosophila, an established model of kidney disease, was used to develop an in vivo functional screen to determine causation forCOL4A5genetic variants linked to Alport syndrome, a progressive nephropathy.