Background and objectives FSGS and nephrotic syndrome studies have shown that single gene causes are more likely to be found in pediatric cases than adults. Consequently, many studies have examined limited gene panels in largely pediatric cohorts. Design, setting, participants, & measurements Whole-exome sequencing was performed in adults with FSGS diagnosed between 1976 and 2017 in the Toronto GN Registry. An expanded panel of 109 genes linked to FSGS, glomerular basement membrane abnormalities, as well as causes of pediatric ESKD including congenital abnormalities of the kidney and urinary tract (CAKUT) and nephronophthisis, were examined. Results The cohort was composed of 193 individuals from 179 families. Nearly half (49%) developed ESKD at a mean age of 47617 years. The genetic diagnostic rate was 11%. Of definitely pathogenic variants, 55% were in COL4A (A3/A4/A5), 40% were in podocyte genes, and 5% were in CAKUT genes. Many, but not all individuals with COL4A definitely pathogenic variants had some evidence of glomerular basement membrane abnormalities. The estimated mean survival/age of kidney failure for individuals with COL4A definitely pathogenic variants was 58 years (95% confidence interval, 49 to 69), far later than what has been reported in the literature. Likely pathogenic variants were identified in an additional 9% of the cohort, with most in COL4A. Correlation with glomerular basement membrane morphology suggested a causal role for at least some of these likely pathogenic variants. Conclusions Even with an expanded gene panel, we find that COL4A disorders are the leading monogenic cause in adults diagnosed with FSGS.

Key points Body Na+ content is tightly controlled by regulated urinary Na+ excretion.The intrarenal mechanisms mediating adaptation to variations in dietary Na+ intake are incompletely characterized.We confirmed and expanded observations in mice that variations in dietary Na+ intake do not alter the glomerular filtration rate but alter the total and cell‐surface expression of major Na+ transporters all along the kidney tubule.Low dietary Na+ intake increased Na+ reabsorption in the proximal tubule and decreased it in more distal kidney tubule segments.High dietary Na+ intake decreased Na+ reabsorption in the proximal tubule and increased it in distal segments with lower energetic efficiency.The abundance of apical transporters and Na+ delivery are the main determinants of Na+ reabsorption along the kidney tubule.Tubular O2 consumption and the efficiency of sodium reabsorption are dependent on sodium diet. AbstractNa+ excretion by the kidney varies according to dietary Na+ intake. We undertook a systematic study of the effects of dietary salt intake on glomerular filtration rate (GFR) and tubular Na+ reabsorption. We examined the renal adaptive response in mice subjected to 7 days of a low sodium diet (LSD) containing 0.01% Na+, a normal sodium diet (NSD) containing 0.18% Na+ and a moderately high sodium diet (HSD) containing 1.25% Na+. As expected, LSD did not alter measured GFR and increased the abundance of total and cell‐surface NHE3, NKCC2, NCC, α‐ENaC and cleaved γ‐ENaC compared to NSD. Mathematical modelling predicted that tubular Na+ reabsorption increased in the proximal tubule but decreased in the distal nephron because of diminished Na+ delivery. This prediction was confirmed by the natriuretic response to diuretics targeting the thick ascending limb, the distal convoluted tubule or the collecting system. On the other hand, HSD did not alter measured GFR but decreased the abundance of the aforementioned transporters compared to NSD. Mathematical modelling predicted that tubular Na+ reabsorption decreased in the proximal tubule but increased in distal segments with lower transport efficiency with respect to O2 consumption. This prediction was confirmed by the natriuretic response to diuretics. The activity of the metabolic sensor adenosine monophosphate‐activated protein kinase (AMPK) was related to the changes in tubular Na+ reabsorption. Our data show that fractional Na+ reabsorption is distributed differently according to dietary Na+ intake and induces changes in tubular O2 consumption and sodium transport efficiency.

Water accumulation in the interstitium (edema) and the peritoneum (ascites) of nephrotic patients is classically thought to stem from the prevailing low plasma albumin concentration and the decreased transcapillary oncotic pressure gradient. However, several clinical and experimental observations suggest that it might also stem from changes in capillary permeability. We addressed this hypothesis by studying the peritoneum permeability of rats with puromycin aminonucleosideinduced nephrotic syndrome. The peritoneum of puromycin aminonucleoside rats displayed an increase in the water filtration coefficient of paracellular and transcellular pathways, and a decrease in the reflection coefficient to proteins. It also displayed oxidative stress and subsequent activation of NF-B. Scavenging of reactive oxygen species and inhibition of NF-B prevented the changes in the water permeability and reflection coefficient to proteins and reduced the volume of ascites by over 50%. Changes in water permeability were associated with the overexpression of the water channel aquaporin 1, which was prevented by reactive oxygen species scavenging and inhibition of NF-B. In conclusion, nephrotic syndrome is associated with an increased filtration coefficient of the peritoneum and a decreased reflection coefficient to proteins. These changes, which account for over half of ascite volume, are triggered by oxidative stress and subsequent activation of NF-B. Nephrotic syndrome (NS)3 is a multifactorial glomerular disease defined by massive proteinuria and hypoalbuminemia. Irrespective of its etiology, NS is commonly associated with renal retention of sodium leading to the generation of ascites and/or edema (1, 2). Association of sodium retention with edema rather than with hypertension suggests that fluid flux across the capillary endothelium increases, and accordingly the capillary filtration capacity is 2-fold higher in nephrotic patients (3). Classically, this increase is thought to stem from hypoalbuminemia and a decreased oncotic gradient across the capillary wall. However, several observations militate against this theory: 1) the transcapillary gradient of oncotic pressure is almost unchanged in nephrotic patients (4, 5); 2) during steroid-induced remission of nephrotic syndrome, natriuresis resumes and edema decreases before normalization of serum albumin levels (6); and 3) diuretic treatments reduce edema without significantly changing the oncotic pressure gradient (5). Consequently, a new concept has emerged according to which the asymmetry of volume expansion in NS results from alterations of the intrinsic properties of the endothelial filtration barrier, i.e. its water permeability and/or its reflection coefficient to proteins. However, this hypothesis has not been demonstrated experimentally, and neither the molecular basis of these capillary alterations nor their connection to proteinuria and/or hypoalbuminemia is elucidated. Several studies have highlighted the pathophysiological importance of reactive oxygen species (ROS) in ...