Mechanisms of pathogenicity and the quest for genetic modifiers of kidney disease in branchiootorenal syndrome

Sebastian Sewerin; Charlotte Aurnhammer; Cene Skubic; Kaja Blagotinšek Cokan; Jera Jeruc; Damjana Rozman; Frederick Pfister; Katalin Dittrich; Brigitte Mayer; Ria Schönauer; Friederike Petzold; Jan Halbritter

doi:10.1093/ckj/sfad260

Mechanisms of pathogenicity and the quest for genetic modifiers of kidney disease in branchiootorenal syndrome

Clin Kidney J. 2023 Oct 13;17(1):sfad260. doi: 10.1093/ckj/sfad260. eCollection 2024 Jan.

Authors

Sebastian Sewerin^{1

2}, Charlotte Aurnhammer¹, Cene Skubic³, Kaja Blagotinšek Cokan³, Jera Jeruc⁴, Damjana Rozman³, Frederick Pfister^{5

6}, Katalin Dittrich⁷, Brigitte Mayer⁸, Ria Schönauer^{1

9}, Friederike Petzold¹, Jan Halbritter^{1

9}

Affiliations

¹ Division of Nephrology, University of Leipzig Medical Center, Leipzig, Germany.
² Current affiliation: Broad Institute of MIT and Harvard, Cambridge, MA, USA.
³ Institute of Biochemistry, Centre for Functional Genomics and Bio-Chips, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia.
⁴ Institute of Pathology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia.
⁵ Institute of Pathology, University of Erlangen Medical Center, Erlangen, Germany.
⁶ Current affiliation: Humanpathologie Dr. med. Manfred Weiß MVZ GmbH, Erlangen-Tennenlohe, Germany.
⁷ Division of Pediatric Nephrology, University of Leipzig Medical Center, Leipzig, Germany.
⁸ Division of Pediatric Nephrology, University of Dresden Medical Center, Dresden, Germany.
⁹ Current affiliation: Department of Nephrology and Medical Intensive Care, Charité Universitätsmedizin Berlin, Berlin, Germany.

Abstract

Backgound: Branchiootorenal (BOR) syndrome is an autosomal dominant disorder caused by pathogenic EYA1 variants and clinically characterized by auricular malformations with hearing loss, branchial arch anomalies, and congenital anomalies of the kidney and urinary tract. BOR phenotypes are highly variable and heterogenous. While random monoallelic expression is assumed to explain this phenotypic heterogeneity, the potential role of modifier genes has not yet been explored.

Methods: Through thorough phenotyping and exome sequencing, we studied one family with disease presentation in at least four generations in both clinical and genetic terms. Functional investigation of the single associated EYA1 variant c.1698+1G>A included splice site analysis and assessment of EYA1 distribution in patient-derived fibroblasts. The candidate modifier gene CYP51A1 was evaluated by histopathological analysis of murine Cyp51^+/^- and Cyp51^-/- kidneys. As the gene encodes the enzyme lanosterol 14α-demethylase, we assessed sterol intermediates in patient blood samples as well.

Results: The EYA1 variant c.1698+1G>A resulted in functional deletion of the EYA domain by exon skipping. The EYA domain mediates protein-protein interactions between EYA1 and co-regulators of transcription. EYA1 abundance was reduced in the nuclear compartment of patient-derived fibroblasts, suggesting impaired nuclear translocation of these protein complexes. Within the affected family, renal phenotypes spanned from normal kidney function in adulthood to chronic kidney failure in infancy. By analyzing exome sequencing data for variants that potentially play roles as genetic modifiers, we identified a canonical splice site alteration in CYP51A1 as the strongest candidate variant.

Conclusion: In this study, we demonstrate pathogenicity of EYA1 c.1698+1G>A, propose a mechanism for dysfunction of mutant EYA1, and conjecture CYP51A1 as a potential genetic modifier of renal involvement in BOR syndrome.

Keywords: branchiootorenal syndrome; chronic kidney disease; modifier genes; patient-derived fibroblasts; phenotypic heterogeneity.