C3 glomerulopathy is a recently introduced pathological entity whose original definition was glomerular pathology characterized by C3 accumulation with absent or scanty immunoglobulin deposition. In August 2012, an invited group of experts (comprising the authors of this document) in renal pathology, nephrology, complement biology, and complement therapeutics met to discuss C3 glomerulopathy in the first C3 Glomerulopathy Meeting. The objectives were to reach a consensus on: the definition of C3 glomerulopathy, appropriate complement investigations that should be performed in these patients, and how complement therapeutics should be explored in the condition. This meeting report represents the current consensus view of the group.

A priori clinical diagnosis of CKD is defined as pre-WES clinical diagnosis per referral by primary nephrologist. CAKUT, congenital anomalies of the kidney and urinary tract; CKD, chronic kidney disease; ESKD, end-stage kidney disease; GN, glomerulonephritis; SRNS, steroid-resistant nephrotic syndrome; TIKD, tubulointerstitial kidney disease; WES, whole exome sequencing. a Age at first presentation to medical services with evidence of CKD. b Age at start of renal replacement therapy, i.e., dialysis or kidney transplantation. DM Connaughton et al.: Monogenic causation of chronic kidney disease in Ireland c l i n i c a l i n v e s t i g a t i o n Kidney International (2019) 95, 914-928 DM Connaughton et al.: Monogenic causation of chronic kidney disease in Ireland c l i n i c a l i n v e s t i g a t i o n

The specialized epithelial cell of the kidney, the podocyte, has a complex actin-based cytoskeleton. Dynamic regulation of this cytoskeleton is required for efficient barrier function of the kidney. Podocytes are a useful cell type to study the control of the actin cytoskeleton in vivo, because disruption of components of the cytoskeleton results in podocyte damage, cell loss, and a prototypic injury response called focal segmental glomerulosclerosis (FSGS). Searching for actin regulatory proteins that are expressed in podocytes, we identified a RhoA-activated Rac1 GTPase-activating protein (Rac1-GAP), Arhgap24, that was upregulated in podocytes as they differentiated, both in vitro and in vivo. Increased levels of active Rac1 and Cdc42 were measured in Arhgap24 knockdown experiments, which influenced podocyte cell shape and membrane dynamics. Consistent with a role for Arhgap24 in normal podocyte functioning in vivo, sequencing of the ARHGAP24 gene in patients with FSGS identified a mutation that impaired its Rac1-GAP activity and was associated with disease in a family with FSGS. Thus, Arhgap24 contributes to the careful balancing of RhoA and Rac1 signaling in podocytes, the disruption of which may lead to kidney disease.

Mutations in the canonical transient receptor potential cation channel 6 (TRPC6) are responsible for familial forms of adult onset focal segmental glomerulosclerosis (FSGS). The mechanisms by which TRPC6 mutations cause kidney disease are not well understood. We used TRPC6-deficient mice to examine the function of TRPC6 in the kidney. We found that adult TRPC6-deficient mice had BP and albumin excretion rates similar to wild-type animals. Glomerular histomorphology revealed no abnormalities on both light and electron microscopy. To determine whether the absence of TRPC6 would alter susceptibility to hypertension and renal injury, we infused mice with angiotensin II continuously for 28 days. Although both groups developed similar levels of hypertension, TRPC6-deficient mice had significantly less albuminuria, especially during the early phase of the infusion; this suggested that TRPC6 adversely influences the glomerular filter. We used whole-cell patch-clamp recording to measure cellmembrane currents in primary cultures of podocytes from both wild-type and TRPC6-deficient mice. In podocytes from wild-type mice, angiotensin II and a direct activator of TRPC6 both augmented cellmembrane currents; TRPC6 deficiency abrogated these increases in current magnitude. Our findings suggest that TRPC6 promotes albuminuria, perhaps by promoting angiotensin II-dependent increases in Ca 2ϩ , suggesting that TRPC6 blockade may be therapeutically beneficial in proteinuric kidney disease. The transient receptor potential (TRP) ion channel family is a diverse group of cation channels identified by a common primary structure with six membrane-spanning domains and intracellular carboxy and amino termini. Within the larger group of TRP channels, the TRPC family is characterized by three or four amino-terminal ankyrin repeats and a highly conserved TRP domain. Within the TRPC family, TRPC6 is 75% homologous at the amino acid level with TRPC3 and TRPC7, and all three are activated by diacylglycerol. They are believed to associate as heterotrimers to form functional ion channels on the cell surface. 1 A role for TRPC6 in the kidney was revealed by studies showing that mutations in the TRPC6 gene cause autosomal dominant forms of hereditary focal segmental glomerulosclerosis (FSGS) that are particularly aggressive. We originally reported that patients with the TRPC6 P112Q mutation developed high-grade proteinuria by the third or fourth decade of life, and 60% progressed to ESRD. 2 We also found augmented intracellular calcium (Ca 2ϩ ) influx with TRPC6 P112Q compared with wild-type