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Background The Flemish Collaborative Glomerulonephritis Group (FCGG) registry is the first population-based native kidney biopsy registry in Flanders, Belgium. In this first analysis, we report on patient demographics, frequency distribution and incidence rate of biopsied kidney disease in adults in Flanders. Methods From January 2017 to December 2019, a total of 2054 adult first native kidney biopsies were included. A ‘double diagnostic coding’ strategy was used, in which every biopsy sample received a histopathological and final clinical diagnosis. Frequency distribution and incidence rate of both diagnoses were reported and compared with other European registries. Results The median age at biopsy was 61.1 years (interquartile range, 46.1–71.7); male patients were more prevalent (62.1%) and biopsy incidence rate was 129.3 per million persons per year. Immunoglobulin A nephropathy was the most frequently diagnosed kidney disease (355 biopsies, 17.3% of total) with a similar frequency as in previously published European registries. The frequency of tubulointerstitial nephritis (220 biopsies, 10.7%) and diabetic kidney disease (154 biopsies, 7.5%) was remarkably higher, which may be attributed to changes in disease incidence as well as biopsy practices. Discordances between histopathological and final clinical diagnoses were noted and indicate areas for improvement in diagnostic coding systems. Conclusions The FCGG registry, with its ‘double diagnostic coding’ strategy, provides useful population-based epidemiological data on a large Western European population and allows subgroup selection for future research.

Lay Summary The Flemish Collaborative Glomerulonephritis Group (FCGG) registry collects information on patients that undergo kidney biopsy in the region of Flanders in Belgium. The registry summarizes the underlying diagnoses in patients that present with symptoms of kidney disease (e.g. blood and/or protein in the urine or decreased kidney function). Additionally, the registry also collects information on the degree of chronic damage on kidney biopsy. This is important because chronic damage may lead to kidney failure. From 2017 until 2019, a total of 2054 adult biopsies were analyzed, while chronic damage could be analyzed in 898 biopsies. We found that the underlying causes of severe kidney disease were similar to studies performed in other European countries. Importantly, we found that increasing age, reduced kidney function and certain diagnoses are associated with more chronic damage on kidney biopsy. This information may be useful to doctors in clinical practice, in both Belgium and Europe. Background The Flemish Collaborative Glomerulonephritis Group (FCGG) registry provides complete population data on kidney disease epidemiology in the region of Flanders (Belgium), as it captures all native kidney biopsies performed in its population of 6.5 million inhabitants. Methods From 2017 until 2019, 2054 adult kidney biopsies were included from 26 nephrology centers (one biopsy per patient). Data on nephrotic and nephritic syndrome were available in 1992 and 2026 biopsies, respectively. In a subgroup of 898 biopsies containing >= 10 glomeruli from 2018 to 2019, disease chronicity was graded using the Mayo Clinic Chronicity Score (MCCS). The association between clinical variables and MCCS was determined using simple and multiple linear regression models. Results Nephrotic syndrome (present in 378 patients, 19.0%) was most frequently caused by minimal change disease in younger patients (18-44 years), membranous nephropathy in older patients (45-74 years) and amyloidosis in the elderly (>75 years). Nephritic syndrome (present in 421 patients, 20.8%) was most frequently caused by immunoglobulin A nephropathy (IgAN) in younger patients (18-64 years) and ANCA-associated vasculitis (AAV) in older patients (>64 years). AAV and IgAN were the most frequent underlying diagnoses in biopsies in which crescents were identified. In multivariable analysis, acute and chronic kidney disease and diagnoses of diabetic kidney disease, nephrosclerosis and hyperoxaluria/hypercalcemic nephropathy were associated with the highest MCCS increases. Conclusions The FCGG registry validates data from previous Western European registries and provides a snapshot of disease chronicity in the whole biopsied Flemish population. D.D. is supported by a PhD Fellowship grant fundamental research from the Research Foundation Flanders (F.W.O., grant number 11L5622N). B.S. is a senior clinical investigator of The Research Foundation Flanders (F.W.O., grant number 1 842 919 N). The FCGG registry is funded by the Nederlandstalige Belgische Vereniging voor Nefrologie (NBVN). The authors wish to thank all collaborating nephrologists in Flanders and Brussels and responsible persons at the data entry centers (Elsie De Man, Sabine Verhofstede, Ben Sprangers) for their participation in the FCGG registry. The FCGG registry was initiated in collaboration with the Nederlandstalige Belgische Vereniging voor Nefrologie (NBVN), the organization that represents the majority of nephrologists in the region of Flanders. The study was approved by the Ethical Committee of the University Hospitals Leuven (study reference S59182) and local committees of all participating centers.

Objective: In 2016, a regional renal biopsy network was founded as a collaboration between renal pathologists and nephrologists in order to standardize diagnosis and therapy. Uniform renal biopsy request and renal biopsy report forms were introduced, together with a new comprehensive list of renal pathology diagnoses for coding. The 2017-2018 epidemiological data of the pediatric patients (age= 0-17 years) are presented. Methods: Following informed consent and in compliance with GDPR, data registration consists of basic patient and categorical renal data, semi-structured medical information of renal histopathology and the clinical renal disease. Results: In 2017-2018, 92 renal biopsies were reported in pediatric patients or 3.6 per 100,000 pediatric inhabitants per year. Three clinical patterns were equally represented: only proteinuria >1g/day; only hematuria; and combination of proteinuria and hematuria. Acute or chronic renal failure were rare. In the youngest age group (0-5 years; N=26) minimal change disease predominated, followed by Henoch-Schönlein nephritis. The middle age group (6-11 years; N=32) mainly presented with disease characterized by hematuria: IgA nephropathy, Henoch-Schönlein nephritis and Alport’s disease. A more diverse renal disease spectrum was present in the highest age group (12-18 years; N=34): IgA nephropathy, different forms of proliferative glomerulonephritis and of nephrotic syndrome of childhood. Patients with a Caucasian descent presented with IgA nephropathy, while a nephrotic syndrome was more common in those without a Caucasian descent. Alport’s disease was particularly diagnosed in female patients, IgA nephropathy in male patients, and the gender distribution was equal in minimal change disease. Conclusion: The FCGG network provides an better cross-talk between renal pathologists and nephrologists. For the first time, reliable estimates of pediatric renal diseases based on histology are available. Genetic analyses are not yet included. Efforts to coordinate clinical care of pediatric renal diseases are ongoing

Pseudohypoaldosteronism type 1B (PHA type 1B) is a very rare multi-system salt-wasting disease. Severe life-long salt loss is seen in multiple target organs expressing the amiloride-sensitive epithelial sodium channel (ENaC) including the kidney, sweat glands, salivary glands, colon and lung. In the lungs, ENaC channels are located on the motile cilia and regulate the osmolarity of the periciliary liquid, necesarry for a normal motile cilia function. The loss-of- function of ENaC in PHA type 1B patients leads to an increase in the airway surface liquid (ASL), resulting in ‘intrapulmonary drowning’. Patients present with recurrent episodes of chest congestion, coughing, and wheezing. Despite the different pathophysiology, this pulmonary syndrome with increased sweat and saliva electrolyte can easily be confused with cystic fibrosis (CF). We report a case of PHA type 1B with a very severe respiratory phenotype. Reviewing all other PHA type 1B patients with respiratory symptoms, it seems that our patient presents the most severe respiratory course ever described. Up to now, the pulmonary phenotype in PHA type 1B can not be predicted. Nevertheless, it would be useful for the follow-up of these patients, resulting in a better long-term prognosis. To our knowledge, a respiratory comorbidity like asthma could be such a predictor. More research is needed on this topic.

FCGG Renal Biopsy Network: first epidemiological report on pediatric renal diseases Sevasti Karamaria1, Johan De Meester2, Amélie Dendooven3, Elena Levtchenko4, Noel Knops4, Koen Van Hoeck5, Dominique Trouet5, Reiner Mauel6, Ben Sprangers7, Wim Laurens8, Johan Vande Walle1, on behalf of the FCGG – NBVN working group 1 Department of Pediatrics, UZ Gent, Ghent; 2NBVN, Antwerp; 3Pathology Department, UZ Gent, Ghent; 4Department of Pediatrics, UZ Leuven, Leuven; 5Departement of Pediatrics, UZ Antwerpen, Antwerp; 6Department of Pediatrics, UZ Brussel, Brussels; 7Department of Nephrology, UZ Leuven, Leuven; 8Department of Nephrology, AZ Nikolaas, Sint-Niklaas. Objective: In 2016, a regional renal biopsy network was founded as a collaboration between renal pathologists and nephrologists in order to standardize diagnosis and therapy. Uniform renal biopsy request and renal biopsy report forms were introduced, together with a new comprehensive list of renal pathology diagnoses for coding. The 2017-2018 epidemiological data of the pediatric patients (age= 0-17 years) are presented. Methods: Following informed consent and in compliance with GDPR, data registration consists of basic patient and categorical renal data, semi-structured medical information of renal histopathology and the clinical renal disease. Results: In 2017-2018, 92 renal biopsies were reported in pediatric patients or 3.6 per 100,000 pediatric inhabitants per year. Three clinical patterns were equally represented: only proteinuria >1g/day; only hematuria; and combination of proteinuria and hematuria. Acute or chronic renal failure were rare. In the youngest age group (0-5 years; N=26) minimal change disease predominated, followed by Henoch-Schönlein nephritis. The middle age group (6-11 years; N=32) mainly presented with disease characterized by hematuria: IgA nephropathy, Henoch-Schönlein nephritis and Alport’s disease. A more diverse renal disease spectrum was present in the highest age group (12-18 years; N=34): IgA nephropathy, different forms of proliferative glomerulonephritis and of nephrotic syndrome of childhood. Patients with a Caucasian descent presented with IgA nephropathy, while a nephrotic syndrome was more common in those without a Caucasian descent. Alport’s disease was particularly diagnosed in female patients, IgA nephropathy in male patients, and the gender distribution was equal in minimal change disease. Conclusion: The FCGG network provides an better cross-talk between renal pathologists and nephrologists. For the first time, reliable estimates of pediatric renal diseases based on histology are available. Genetic analyses are not yet included. Efforts to coordinate clinical care of pediatric renal diseases are ongoing.