A homozygous missense variant in VWA2, encoding an interactor of the Fraser-complex, in a patient with vesicoureteral reflux

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most common cause (40-50%) of chronic kidney disease (CKD) in children. About 40 monogenic causes of CAKUT have so far been discovered. To date less than 20% of CAKUT cases can be explained by mutations in these 40 genes. To identify additional monogenic causes of CAKUT, we performed whole exome sequencing (WES) and homozygosity mapping (HM) in a patient with CAKUT from Indian origin and consanguineous descent. We identified a homozygous missense mutation (c.1336C>T, p.Arg446Cys) in the gene Von Willebrand factor A domain containing 2 (VWA2). With immunohistochemistry studies on kidneys of newborn (P1) mice, we show that Vwa2 and Fraser extracellular matrix complex subunit 1 (Fras1) co-localize in the nephrogenic zone of the renal cortex. We identified a pronounced expression of Vwa2 in the basement membrane of the ureteric bud (UB) and derivatives of the metanephric mesenchyme (MM). By applying in vitro assays, we demonstrate that the Arg446Cys mutation decreases translocation of monomeric VWA2 protein and increases translocation of aggregated VWA2 protein into the extracellular space. This is potentially due to the additional, unpaired cysteine residue in the mutated protein that is used for intermolecular disulfide bond formation. VWA2 is a known, direct interactor of FRAS1 of the Fraser-Complex (FC). FC-encoding genes and interacting proteins have previously been implicated in the pathogenesis of syndromic and/or isolated CAKUT phenotypes in humans. VWA2 therefore constitutes a very strong candidate in the search for novel CAKUT-causing genes. Our results from in vitro experiments indicate a dose-dependent neomorphic effect of the Arg446Cys homozygous mutation in VWA2.

PloS one. 2018 Jan 19*** epublish ***

Amelie T van der Ven, Birgit Kobbe, Stefan Kohl, Shirlee Shril, Hans-Martin Pogoda, Thomas Imhof, Hadas Ityel, Asaf Vivante, Jing Chen, Daw-Yang Hwang, Dervla M Connaughton, Nina Mann, Eugen Widmeier, Mary Taglienti, Johanna Magdalena Schmidt, Makiko Nakayama, Prabha Senguttuvan, Selvin Kumar, Velibor Tasic, Elijah O Kehinde, Shrikant M Mane, Richard P Lifton, Neveen Soliman, Weining Lu, Stuart B Bauer, Matthias Hammerschmidt, Raimund Wagener, Friedhelm Hildebrandt

Division of Nephrology, Department of Medicine, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, United States of America., Center for Biochemistry, Center for Molecular Medicine Cologne, University of Cologne, Cologne, Germany., Institute of Zoology-Developmental Biology, Biocenter Cologne, Center for Molecular Medicine Cologne, University of Cologne, Cologne, Germany., Institute for Dental Research and Oral Musculoskeletal Biology, Medical Faculty, University of Cologne, Cologne, Germany., Department of Pediatric Nephrology, Dr. Mehta's Multispeciality Hospital, Chennai, India., Department of Pediatric Nephrology, Institute of Child Health and Hospital for Children, the Tamil Nadu Dr. M.G.R. Medical University, Chennai, Tamil Nadu, India., Medical Faculty Skopje, University Children's Hospital, Skopje, Macedonia., Division of Urology, Department of Surgery, Nazarbayev University, Astana, Kazakhstan., Department of Genetics, Yale University School of Medicine, New Haven, Connecticut, United States of America., Department of Pediatrics, Center of Pediatric Nephrology & Transplantation, Cairo University, Egyptian Group for Orphan Renal Diseases, Cairo, Egypt., Renal Section, Department of Medicine, Boston University Medical Center, Boston, Massachusetts, United States of America., Department of Urology, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts, United States of America.