A functional variant in NEPH3 gene confers high risk of renal failure in primary hematuric glomerulopathies. Evidence for predisposition to microalbuminuria in the general population.
BACKGROUND
Recent data emphasize that thin basement membrane nephropathy (TBMN) should not be viewed as a form of benign familial hematuria since chronic renal failure (CRF) and even end-stage renal disease (ESRD), is a possible development for a subset of patients on long-term follow-up, through the onset of focal and segmental glomerulosclerosis (FSGS). We hypothesize that genetic modifiers may explain this variability of symptoms.


METHODS
We looked in silico for potentially deleterious functional SNPs, using very strict criteria, in all the genes significantly expressed in the slit diaphragm (SD). Two variants were genotyped in a cohort of well-studied adult TBMN patients from 19 Greek-Cypriot families, with a homogeneous genetic background. Patients were categorized as "Severe" or "Mild", based on the presence or not of proteinuria, CRF and ESRD. A larger pooled cohort (HEMATURIA) of 524 patients, including IgA nephropathy patients, was used for verification. Additionally, three large general population cohorts [Framingham Heart Study (FHS), KORAF4 and SAPHIR] were used to investigate if the NEPH3-V353M variant has any renal effect in the general population.


CONCLUSIONS
Genotyping for two high-scored variants in 103 TBMN adult patients with founder mutations who were classified as mildly or severely affected, pointed to an association with variant NEPH3-V353M (filtrin). This promising result prompted testing in the larger pooled cohort (HEMATURIA), indicating an association of the 353M variant with disease severity under the dominant model (p = 3.0x10-3, OR = 6.64 adjusting for gender/age; allelic association: p = 4.2x10-3 adjusting for patients' kinships). Subsequently, genotyping 6,531 subjects of the Framingham Heart Study (FHS) revealed an association of the homozygous 353M/M genotype with microalbuminuria (p = 1.0x10-3). Two further general population cohorts, KORAF4 and SAPHIR confirmed the association, and a meta-analysis of all three cohorts (11,258 individuals) was highly significant (p = 1.3x10-5, OR = 7.46). Functional studies showed that Neph3 homodimerization and Neph3-Nephrin heterodimerization are disturbed by variant 353M. Additionally, 353M was associated with differential activation of the unfolded protein response pathway, when overexpressed in stressed cultured undifferentiated podocyte cells, thus attesting to its functional significance. Genetics and functional studies support a "rare variant-strong effect" role for NEPH3-V353M, by exerting a negative modifier effect on primary glomerular hematuria. Additionally, genetics studies provide evidence for a role in predisposing homozygous subjects of the general population to micro-albuminuria.
Department of Biological Sciences and Molecular Medicine Research Center, University of Cyprus, Nicosia, Cyprus.
Konstantinos
K
Voskarides
Department of Biological Sciences and Molecular Medicine Research Center, University of Cyprus, Nicosia, Cyprus.
Charalambos
C
Stefanou
Department of Biological Sciences and Molecular Medicine Research Center, University of Cyprus, Nicosia, Cyprus.
Myrtani
M
Pieri
Department of Biological Sciences and Molecular Medicine Research Center, University of Cyprus, Nicosia, Cyprus.
Panayiota
P
Demosthenous
Department of Biological Sciences and Molecular Medicine Research Center, University of Cyprus, Nicosia, Cyprus.
Kyriakos
K
Felekkis
Department of Nephrology, Limassol General Hospital, Limassol, Cyprus.
Maria
M
Arsali
Department of Nephrology, Nicosia General Hospital, Nicosia, Cyprus.
Yiannis
Y
Athanasiou
Department of Nephrology, University of Crete, Heraklion, Crete, Greece.
Dimitris
D
Xydakis
Department of Nephrology, University of Crete, Heraklion, Crete, Greece.
Kostas
K
Stylianou
Department of Nephrology, University of Crete, Heraklion, Crete, Greece.
Eugenios
E
Daphnis
Department of Internal Medicine, Section of Molecular Medicine and Human Genetics, Medical School, University of Crete, Heraklion, Greece.
Giorgos
G
Goulielmos
Private Clinical Laboratory, Paralimni, Cyprus.
Petros
P
Loizou
Department of Medicine, The University of Melbourne, Northern Health, Epping, Australia.
Judith
J
Savige
Department 2 of Internal Medicine and Center for Molecular Medicine Cologne, University of Cologne, Cologne, Germany.|Systems Biology of Ageing Cologne (Sybacol), University of Cologne, Cologne, Germany.
Martin
M
Höhne
Department 2 of Internal Medicine and Center for Molecular Medicine Cologne, University of Cologne, Cologne, Germany.
Linus A
LA
Völker
Department 2 of Internal Medicine and Center for Molecular Medicine Cologne, University of Cologne, Cologne, Germany.|Systems Biology of Ageing Cologne (Sybacol), University of Cologne, Cologne, Germany.|Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, Cologne, Germany.
Thomas
T
Benzing
Division of Medicine, University College London, London, United Kingdom.
Patrick H
PH
Maxwell
UCL Centre for Nephrology, University College London, London, United Kingdom.
Daniel P
DP
Gale
Department of Nephrology, University Hospital Regensburg, Regensburg, Germany.|Department of Genetic Epidemiology, University Regensburg, Regensburg, Germany.
Mathias
M
Gorski
Department of Nephrology, University Hospital Regensburg, Regensburg, Germany.
Carsten
C
Böger
Division of Genetic Epidemiology, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Innsbruck, Austria.
Barbara
B
Kollerits
Division of Genetic Epidemiology, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Innsbruck, Austria.
Florian
F
Kronenberg
First Department of Internal Medicine, Paracelsus Private Medical University Salzburg, Salzburg, Austria.
Bernhard
B
Paulweber
Department of Nephrology, Nicosia General Hospital, Nicosia, Cyprus.
Michalis
M
Zavros
Department of Nephrology, Hippocrateon Hospital, Nicosia, Cyprus.
Alkis
A
Pierides
Department of Biological Sciences and Molecular Medicine Research Center, University of Cyprus, Nicosia, Cyprus.
Constantinos
C
Deltas
D000328:Adult; D000419:Albuminuria / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D057809:HEK293 Cells; D006417:Hematuria / Q000150:complications* / Q000235:genetics; D006801:Humans; D015151:Immunoblotting; D007136:Immunoglobulins / Q000235:genetics* / Q000502:physiology; D047468:Immunoprecipitation; D007676:Kidney Failure, Chronic / Q000235:genetics; D008297:Male; D008565:Membrane Proteins / Q000235:genetics* / Q000502:physiology; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D051437:Renal Insufficiency / Q000235:genetics*; D012307:Risk Factors
D007136:Immunoglobulins; C482646:KIRREL2 protein, human; D008565:Membrane Proteins