The National Registry of Rare Kidney Diseases (RaDaR): Description, recruitment, and cross-sectional analyses of 25,880 adults and children with rare kidney diseases in the UK
Authors: Wong Katie , Pitcher David , Braddon Fiona , Downward Lewis , Steenkamp Retha , Annear Nicholas , Barratt Jonathan , Bingham Coralie , Coward Richard J. , Chrysochou Tina , Game David , Griffin Sian , Hall Matt , Johnson Sally , Kanigicherla Durga , Frankl Fiona Karet , Kavanagh David , Kerecuk Larissa , Maher Eamonn R. , Moochhala Shabbir , Pinney Jenny , Sayer John A. , Simms Roslyn , Sinha Smeeta , Srivastava Shalabh , Tam Frederick W. K. , Thomas Kay , Neil Turner A. , Walsh Stephen B. , Waters Aoife , Wilson Patricia , Wong Edwin ,   RaDaR consortium, Therese L. Sy Karla , Huang Kui , Ye Jamie , Nitsch Dorothea , Saleem Moin , Bockenhauer Detlef , Bramham Kate , Gale Daniel P. 
Published: September 2023

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 has automatic linkage 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, ethnicity and socioeconomic status of 1) 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 of RaDaR patients with Autosomal Dominant Polycystic Kidney Disease (ADPKD) was compared to the English Census.

We found evidence of some disparities in ethnicity and social deprivation in recruitment to RaDaR, however these were not consistent across all comparisons. Predominant rare kidney diseases in adults 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. Compared with either adults recruited to RaDaR or the English population, children recruited to RaDaR were more likely to be of Asian ethnicity and live in more socially deprived areas.

Lay Summary

Rare kidney diseases make a significant contribution to the number of people living with kidney disease globally: >25% of adults and >50% of children with kidney failure have a rare disease. However, there is a lack of high-quality published data on how these conditions present, and in which patient groups. Patients often face delays in diagnosis and lack of reliable information on their condition once diagnosed. The UK National Registry of Rare Kidney Diseases (RaDaR) was formed in 2010 to address this knowledge gap. It collects long-term data for UK patients with rare kidney conditions, and is the largest rare kidney disease registry in the world. Here, we present information about 25,880 adults and children recruited to RaDaR, including ethnicity, socioeconomic status, and kidney function, and investigate whether there is any bias in recruitment to RaDaR. To our knowledge, this is the largest epidemiological description of rare kidney diseases worldwide.