The National Registry of Rare Kidney Diseases (RaDaR): design, recruitment, and cross-sectional analyses of 25,880 adults and children with rare kidney diseases in the UK

Rare kidney diseases are not well characterised, despite making a significant contribution to the burden of kidney disease globally. The National Registry of Rare Kidney Diseases (RaDaR) collects longitudinal disease and treatment related data from people living with rare kidney diseases across the UK, and is the largest rare kidney disease registry in the world. We present the clinical demographics and renal function of 25,880 prevalent patients and evaluate for any potential recruitment bias to RaDaR. RaDaR recruits patients from 108 UK hospitals and is linked with the UK Renal Registry (UKRR, with which all UK patients receiving Kidney Replacement Therapy (KRT) are registered). To assess for recruitment bias to RaDaR we performed three comparisons of ethnicity and socioeconomic status: 1) All prevalent RaDaR patients receiving KRT were compared with patients with eligible rare disease diagnoses receiving KRT in the UKRR 2) Patients recruited to RaDaR and all eligible unrecruited patients at two renal centres were compared 3) The age-stratified ethnicity distribution RaDaR patients with Autosomal Dominant Polycystic Kidney Disease (ADPKD) was compared with the English Census. We observed over-representation of individuals reporting South Asian ethnicity in some rare diseases (most markedly Cystinosis and Primary Hyperoxaluria). We found no evidence of systematic bias in recruitment to RaDaR in terms of ethnicity or social deprivation. Predominant rare kidney diseases in adults (≥18 years) were ADPKD (29.2%), Vasculitis (15.8%) and IgA nephropathy (15.7%), compared to Idiopathic nephrotic syndrome (43.6%), Vasculitis (10.8%) and Alport Syndrome (5.9%) in children (<18 years). Compared with either adults recruited to RaDaR or the general UK population, children recruited to RaDaR were more likely to be of Asian ethnicity and live in more socially deprived areas. ### Competing Interest Statement Katie Wong, David Pitcher, Fiona Braddon, Retha Steenkamp, Lewis Downward, Nicholas Annear, Jonathan Barratt, Coralie Bingham, Kate Bramham , Richard J. Coward, Tina Chrysochou, David Game, Sian Griffin, Matthew Hall, Sally Johnson, Durga Kanigicherla, Fiona Karet Frankl, David Kavanagh, Larissa Kerecuk, Shabbir Moochhala, Jennifer Pinney, John A. Sayer, Roslyn Simms, Smeeta Sinha, Shalabh Srivastava, Frederick W. K. Tam, A. Neil Turner, Stephen B. Walsh, Aoife Waters, Patricia Wilson, Edwin Wong, Dorothea Nitsch, Detlef Bockenhauer declare no competing interests as they relate to the current manuscript. Karla Therese L. Sy, Kui Huang and Jamie Ye declare employment with Pfizer Inc. Eamonn R. Maher declares support for the current manuscript from VHL UK/Ireland. Moin Saleem declares support for the current manuscript from a Medical Research Council UK Precision Medicine program grant - MR/R013942/1. Daniel P Gale declares support for the current manuscript from the Medical Research Council, Kidney Research UK, Kidney Care UK, and Polycystic Kidney Disease Charity (payments to institution). ### Funding Statement RaDaR has received support from The UK Medical Research Council, Kidney Research UK, Kidney Care UK and the Polycystic Kidney Disease Charity. This study was partly supported by Pfizer Inc. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Research Ethics committee of NHS South-West-Central Bristol gave ethical approval for this work (19/SW/0173) I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The minimal underlying dataset cannot be included as it contains confidential, potentially identifying and sensitive patient information. The UK Kidney Association(UKKA) is the controller of the data and restricts sharing of individual level data if there is no direct relationship between the UKKA and the recipient. The data underlying these results are available for researchers who meet the criteria for access to confidential data.