Nephrotic syndrome (NS), the association of gross proteinuria, hypoalbuminaemia, edema, and hyperlipidemia, can be clinically divided into steroid-sensitive (SSNS) and steroid-resistant (SRNS) forms. SRNS regularly progresses to end-stage renal failure. By homozygosity mapping and whole exome sequencing, we here identify recessive mutations in Crumbs homolog 2 (CRB2) in four different families affected by SRNS. Previously, we established a requirement for zebrafish crb2b, a conserved regulator of epithelial polarity, in podocyte morphogenesis. By characterization of a loss-of-function mutation in zebrafish crb2b, we now show that zebrafish crb2b is required for podocyte foot process arborization, slit diaphragm formation, and proper nephrin trafficking. Furthermore, by complementation experiments in zebrafish, we demonstrate that CRB2 mutations result in loss of function and therefore constitute causative mutations leading to NS in humans. These results implicate defects in podocyte apico-basal polarity in the pathogenesis of NS.
Bibliographical noteFunding Information:
We would like to acknowledge the late Michelle Winn (Duke University) for initial attempts at finding human CRB2 mutations. We thank Markus Affolter and Hans Georg Belting for the α-Pdxl2 antibody. Special thanks to Lars Holmgren (Karolinska Institute) and Lena Claesson-Welsh (Uppsala University) for their overall support and encouragement. We thank Leslie Steed for clinical samples, Giselbert Hauptmann and Iris Sol for zebrafish care, and Katarina Garpenstrand and Johan Ledin at the SciLife zebrafish, Uppsala University. The authors also thank the families who contributed to this study. This research was supported by grants from the NIH to F.H. (DK076683, DK086542) and by the Nephcure Foundation to F.H. H.Y.G. is supported by the NephCure-ASN Foundation Kidney Research grant. F.H. is an Investigator of the Howard Hughes Medical Institute and the Warren E. Grupe Professor. A.K. is supported by a HEFC Senior Clinical Lectureship. The research was also supported by the National Institute for Health Research (NIHR) Biomedical Research Centre based at Guy’s and St Thomas’ NHS Foundation Trust and King’s College London, Kids Kidney Research, Kidney Research UK, and the British Kidney Patients Association. We would like to acknowledge RADAR, the UK SRNS study group, especially Dr. Larissa Kerecuk for participation and support. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR, or the Department of Health.
© 2015 The American Society of Human Genetics.
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