Serum uromodulin predicts graft failure in renal transplant recipients

The development of lateral flow devices for urinary biomarkers to assess kidney health

Serum creatinine levels are insensitive to real-time changes in kidney function or injury. There is a growing interest in assessing kidney injury by measuring biomarkers in body fluid. From our previous studies, we identified and reported three urinary biomarkers namely Uromodulin (UMOD), Osteopontin (OPN), and Interleukin-9 (IL-9) to be associated with kidney health. The availability of a rapid point-of-care test for these urinary biomarkers will potentially accelerate its applicability and accessibility. In this study, we aimed to develop novel lateral flow device (LFD) for UMOD, OPN and IL-9. We tested paired antibodies using Enzyme Linked Immunosorbent Assay wherein we observed functionality only for UMOD and OPN and not for IL-9. A conjugation buffer pH of 7.8 and 8.5 was found suitable at a detection antibody concentration of 15 µg/mL for LFD development. The developed LFDs were found to quantitatively measure UMOD standard (LLOD of 80,000 pg/mL) and OPN standard (LLOD of 8600 pg/mL) respectively. The LFD was also able to measure human urinary UMOD and OPN with a percent CV of 12.12 and 5.23 respectively.

Unveiling the Hidden Power of Uromodulin: A Promising Potential Biomarker for Kidney Diseases

Uromodulin, also known as Tamm-Horsfall protein, represents the predominant urinary protein in healthy individuals. Over the years, studies have revealed compelling associations between urinary and serum concentrations of uromodulin and various parameters, encompassing kidney function, graft survival, cardiovascular disease, glucose metabolism, and overall mortality. Consequently, there has been a growing interest in uromodulin as a novel and effective biomarker with potential applications in diverse clinical settings. Reduced urinary uromodulin levels have been linked to an elevated risk of acute kidney injury (AKI) following cardiac surgery. In the context of chronic kidney disease (CKD) of different etiologies, urinary uromodulin levels tend to decrease significantly and are strongly correlated with variations in estimated glomerular filtration rate. The presence of uromodulin in the serum, attributable to basolateral epithelial cell leakage in the thick ascending limb, has been observed. This serum uromodulin level is closely associated with kidney function and histological severity, suggesting its potential as a biomarker capable of reflecting disease severity across a spectrum of kidney disorders. The UMOD gene has emerged as a prominent locus linked to kidney function parameters and CKD risk within the general population. Extensive research in multiple disciplines has underscored the biological significance of the top UMOD gene variants, which have also been associated with hypertension and kidney stones, thus highlighting the diverse and significant impact of uromodulin on kidney-related conditions. UMOD gene mutations are implicated in uromodulin-associated kidney disease, while polymorphisms in the UMOD gene show a significant association with CKD. In conclusion, uromodulin holds great promise as an informative biomarker, providing valuable insights into kidney function and disease progression in various clinical scenarios. The identification of UMOD gene variants further strengthens its relevance as a potential target for better understanding kidney-related pathologies and devising novel therapeutic strategies. Future investigations into the roles of uromodulin and regulatory mechanisms are likely to yield even more profound implications for kidney disease diagnosis, risk assessment, and management.

Recent Advances in Urinary Peptide and Proteomic Biomarkers in Chronic Kidney Disease: A Systematic Review

Biomarker development, improvement, and clinical implementation in the context of kidney disease have been a central focus of biomedical research for decades. To this point, only serum creatinine and urinary albumin excretion are well-accepted biomarkers in kidney disease. With their known blind spot in the early stages of kidney impairment and their diagnostic limitations, there is a need for better and more specific biomarkers. With the rise in large-scale analyses of the thousands of peptides in serum or urine samples using mass spectrometry techniques, hopes for biomarker development are high. Advances in proteomic research have led to the discovery of an increasing amount of potential proteomic biomarkers and the identification of candidate biomarkers for clinical implementation in the context of kidney disease management. In this review that strictly follows the PRISMA guidelines, we focus on urinary peptide and especially peptidomic biomarkers emerging from recent research and underline the role of those with the highest potential for clinical implementation. The Web of Science database (all databases) was searched on 17 October 2022, using the search terms "marker *" OR biomarker * AND "renal disease" OR "kidney disease" AND "proteome *" OR "peptid *" AND "urin *". English, full-text, original articles on humans published within the last 5 years were included, which had been cited at least five times per year. Studies based on animal models, renal transplant studies, metabolite studies, studies on miRNA, and studies on exosomal vesicles were excluded, focusing on urinary peptide biomarkers. The described search led to the identification of 3668 articles and the application of inclusion and exclusion criteria, as well as abstract and consecutive full-text analyses of three independent authors to reach a final number of 62 studies for this manuscript. The 62 manuscripts encompassed eight established single peptide biomarkers and several proteomic classifiers, including CKD273 and IgAN237. This review provides a summary of the recent evidence on single peptide urinary biomarkers in CKD, while emphasizing the increasing role of proteomic biomarker research with new research on established and new proteomic biomarkers. Lessons learned from the last 5 years in this review might encourage future studies, hopefully resulting in the routine clinical applicability of new biomarkers.

Role of Uromodulin in Salt-Sensitive Hypertension

The exclusive expression of uromodulin in the kidneys has made it an intriguing protein in kidney and cardiovascular research. Genome-wide association studies discovered variants of uromodulin that are associated with chronic kidney diseases and hypertension. Urinary and circulating uromodulin levels reflect kidney and cardiovascular health as well as overall mortality. More recently, Mendelian randomization studies have shown that genetically driven levels of uromodulin have a causal and adverse effect on kidney function. On a mechanistic level, salt sensitivity is an important factor in the pathophysiology of hypertension, and uromodulin is involved in salt reabsorption via the NKCC2 (Na+-K+-2Cl- cotransporter) on epithelial cells of the ascending limb of loop of Henle. In this review, we provide an overview of the multifaceted physiology and pathophysiology of uromodulin including recent advances in its genetics; cellular trafficking; and mechanistic and clinical studies undertaken to understand the complex relationship between uromodulin, blood pressure, and kidney function. We focus on tubular sodium reabsorption as one of the best understood and pathophysiologically and clinically most important roles of uromodulin, which can lead to therapeutic interventions.

The Perspectives of Biomarkers in Predicting the Survival of the Renal Graft

Kidney transplantation (KT) is currently the elective approach for patients with end-stage renal disease. Although it is a safe choice for these patients, the early complications can lead to graft dysfunction. One of the most redoubtable complications is delayed graft function (DGF), having no specific treatment. The effects of DGF on the graft survival are large enough to justify the formulation of specific biological protocols. Therefore, discovering biomarkers of acute impairment in renal transplanted patients is required. Creatinine is a poor marker to establish the kidney injury. Estimated glomerular filtration rate together with creatinine is ready to approximately measure the kidney function. Different serum and urine proteins are being studied as possible predictive biomarkers for delayed graft function. This review will concentrate on recent and existing research which provide insight concerning the contribution of some molecules for the estimation and evaluation of graft function after kidney transplantation. Further studies examining various aspects of DGF after KT are urgently needed to address a hitherto less-known clinical question.

Pretransplant Serum Uromodulin and Its Association with Delayed Graft Function Following Kidney Transplantation-A Prospective Cohort Study

Delayed graft function (DGF) following kidney transplantation is associated with increased risk of graft failure, but biomarkers to predict DGF are scarce. We evaluated serum uromodulin (sUMOD), a potential marker for tubular integrity with immunomodulatory capacities, in kidney transplant recipients and its association with DGF. We included 239 kidney transplant recipients and measured sUMOD pretransplant and on postoperative Day 1 (POD1) as independent variables. The primary outcome was DGF, defined as need for dialysis within one week after transplantation. In total, 64 patients (27%) experienced DGF. In multivariable logistic regression analysis adjusting for recipient, donor and transplant associated risk factors each 10 ng/mL higher pretransplant sUMOD was associated with 47% lower odds for DGF (odds ratio (OR) 0.53, 95% confidence interval (95%-CI) 0.30–0.82). When categorizing pretransplant sUMOD into quartiles, the quartile with the lowest values had 4.4-fold higher odds for DGF compared to the highest quartile (OR 4.41, 95%-CI 1.54–13.93). Adding pretransplant sUMOD to a model containing established risk factors for DGF in multivariable receiver-operating-characteristics (ROC) curve analysis, the area-under-the-curve improved from 0.786 [95%-CI 0.723–0.848] to 0.813 [95%-CI 0.755–0.871, p = 0.05]. SUMOD on POD1 was not associated with DGF. In conclusion, higher pretransplant sUMOD was independently associated with lower odds for DGF, potentially serving as a non-invasive marker to stratify patients according to their risk for developing DGF early in the setting of kidney transplantation.

Uromodulin: Roles in Health and Disease

Uromodulin, a protein exclusively produced by the kidney, is the most abundant urinary protein in physiological conditions. Already described several decades ago, uromodulin has gained the spotlight in recent years, since the discovery that mutations in its encoding gene UMOD cause a renal Mendelian disease (autosomal dominant tubulointerstitial kidney disease) and that common polymorphisms are associated with multifactorial disorders, such as chronic kidney disease, hypertension, and cardiovascular diseases. Moreover, variations in uromodulin levels in urine and/or blood reflect kidney functioning mass and are of prognostic value for renal function, cardiovascular events, and overall mortality. The clinical relevance of uromodulin reflects its multifunctional nature, playing a role in renal ion transport and immunomodulation, in protection against urinary tract infections and renal stones, and possibly as a systemic antioxidant. Here, we discuss the multifaceted roles of this protein in kidney physiology and its translational relevance.

Current concepts and advances in biomarkers of acute kidney injury

Despite advancements in standardizing the criteria for acute kidney injury (AKI), its definition remains based on changes in serum creatinine and urinary output that do not specifically represent tubular function or injury and that have significant limitations in the acute hospital setting. Much effort in nephrology has centered on identifying biomarkers of AKI to address these limitations. This review summarizes recent advances in our knowledge of biomarkers involved in pathophysiological processes during AKI and describes their potential clinical implications. Blood and urine biomarkers are released via various mechanisms during renal tubular injury. Urinary kidney injury molecule-1 (KIM-1), liver-type fatty acid binding protein (L-FABP), insulin-like growth factor-binding protein-7 (IGFBP-7), and tissue inhibitor of metalloprotease-2 (TIMP-2) are released from the proximal tubule while uromodulin (UMOD) is secreted from the loop of Henle and neutrophil gelatinase-associated lipocalin (NGAL) is released from the distal tubule. These biomarkers could therefore be used to localize specific segments of injured tubules. Biomarkers also have diverse roles in pathophysiological processes in AKI, including inflammation, repair, and fibrosis. Current evidence suggests that these biomarkers could be used to predict the transition to chronic kidney disease (CKD), decrease discard of AKI kidneys, differentiate between kidney dysfunction and injury, guide AKI management, and improve diagnosis of diseases such as acute interstitial nephritis (AIN). They could differentiate between disease phenotypes, facilitate the inclusion of a homogenous patient population in future trials of AKI, and shed light on therapeutic pathways to prevent the transition from AKI to CKD. However, a major limitation of current biomarker research in AKI is the lack of tissue correlation. The Kidney Precision Medicine Project, a large-scale national effort, is currently underway to construct a kidney tissue atlas and expand the use of biomarkers to assess nephron health. Numerous biomarkers are involved in distinct pathophysiological processes after kidney injury and have demonstrated potential to improve diagnosis and risk stratification as well as provide a prognosis for patients with AKI. Some biomarkers are ready for use in clinical trials of AKI and could guide management in various clinical settings. Further investigation of these biomarkers will provide insight that can be applied to develop novel therapeutic agents for AKI.

Serum uromodulin is a novel renal function marker in the Japanese population

BACKGROUND

Uromodulin, also known as Tamm-Horsfall protein, is the most abundant protein in urine. It has recently been reported that uromodulin exists in a small amount in blood and that its concentration correlates with the estimated glomerular filtration rate (eGFR).

METHODS

First, we generated anti-human uromodulin mouse monoclonal antibodies (mAb(s)) and established a specific enzyme-linked immunosorbent assay (ELISA) for uromodulin. We then performed an observational clinical study to determine if there was a correlation between serum uromodulin concentration and estimates of kidney function and whether the serum uromodulin value could be a biomarker in clinical nephrology. The clinical study included 308 patients with and without chronic kidney disease and healthy volunteers. Serum concentrations of creatinine, cystatin C, and uromodulin were measured and correlations were sought between the eGFR calculated from the creatinine and cystatin C levels and the serum uromodulin concentration.

RESULTS

There was a good correlation between the serum uromodulin concentration and the eGFR value calculated from the creatinine (r = 0.76) and cystatin C (r = 0.79) levels. The mean serum uromodulin level in the group with an eGFR > 90 mL/min/1.73 m² calculated using cystatin C was significantly higher than that in the group with an eGFR of 80-89 mL/min/1.73 m².

CONCLUSIONS

The serum uromodulin measurement could be a useful biomarker for identification of patients with early deterioration of kidney function.

Uromodulin (Tamm-Horsfall protein): guardian of urinary and systemic homeostasis

Biology has taught us that a protein as abundantly made and conserved among species as Tamm-Horsfall protein (THP or uromodulin) cannot just be a waste product serving no particular purpose. However, for many researchers, THP is merely a nuisance during urine proteome profiling or exosome purification and for clinicians an enigmatic entity without clear disease implications. Thanks to recent human genetic and correlative studies and animal modeling, we now have a renewed appreciation of this highly prevalent protein in not only guarding urinary homeostasis, but also serving as a critical mediator in systemic inter-organ signaling. Beyond a mere barrier that lines the tubules, or a surrogate for nephron mass, mounting evidence suggests that THP is a multifunctional protein critical for modulating renal ion channel activity, salt/water balance, renal and systemic inflammatory response, intertubular communication, mineral crystallization and bacterial adhesion. Indeed, mutations in THP cause a group of inherited kidney diseases, and altered THP expression is associated with increased risks of urinary tract infection, kidney stone, hypertension, hyperuricemia and acute and chronic kidney diseases. Despite the recent surge of information surrounding THP's physiological functions and disease involvement, our knowledge remains incomplete regarding how THP is normally regulated by external and intrinsic factors, how precisely THP deficiency leads to urinary and systemic pathophysiology and in what clinical settings THP can be used as a theranostic biomarker and a target for modulation to improve patient outcomes.

Uromodulin and microRNAs in Kidney Transplantation-Association with Kidney Graft Function

Uromodulin and microRNAs (miRNAs) have recently been investigated as potential biomarkers for kidney graft associated pathology and outcome, with a special focus on biomarkers indicating specific disease processes and kidney graft survival. The study's aim was to determine whether expression of serum uromodulin concentration and selected miRNAs might be related to renal function in kidney transplant recipients (KTRs). The uromodulin concentration and expression of six selected miRNAs (miR-29c, miR-126, miR-146a, miR-150, miR-155, and miR-223) were determined in the serum of 100 KTRs with stable graft function and chronic kidney disease of all five stages. Kidney graft function was estimated with routine parameters (creatinine, urea, cystatin C, and Chronic Kidney Disease Epidemiology Collaboration study equations) and precisely measured using chromium-51 labelled ethylenediaminetetraacetic-acid clearance. The selected miRNAs were shown to be independent of kidney graft function, indicating their potential as biomarkers of associated kidney graft disease processes. In contrast, the serum uromodulin level depended entirely on kidney graft function and thus reflected functioning tubules rather than any specific kidney graft injury. However, decreased concentrations of serum uromodulin can be observed in the early course of tubulointerstitial injury, thereby suggesting its useful role as an accurate, noninvasive biomarker of early (subclinical) kidney graft injury.

Uromodulin in mineral metabolism

PURPOSE OF REVIEW

Uromodulin (UMOD), also known as Tamm-Horsfall protein, is the most abundant protein in human urine. UMOD has multiple functions such as protection against urinary tract infections and nephrolithiasis. This review outlines recent progress made in UMOD's role in renal physiology, tubular transport, and mineral metabolism.

RECENT FINDINGS

UMOD is mostly secreted in the thick ascending limb (TAL) and to a lesser degree in the distal convoluted tubule (DCT). UMOD secretion is regulated by the calcium-sensing receptor. UMOD upregulates ion channels [e.g., renal outer medullary potassium channel, transient receptor potential cation channel subfamily V member 5, and transient receptor potential melastatin 6 (TRPM6)] and cotransporters [e.g., Na,K,2Cl cotransporter (NKCC2) and sodium-chloride cotransporter (NCC)] in the TAL and DCT. Higher serum UMOD concentrations have been associated with higher renal function and preserved renal reserve. Higher serum UMOD has also been linked to a lower risk of cardiovascular disease and diabetes mellitus.

SUMMARY

With better serum UMOD detection assays the extent of different functions for UMOD is still expanding. Urinary UMOD regulates different tubular ion channels and cotransporters. Variations of urinary UMOD secretion can so contribute to common disorders such as hypertension or nephrolithiasis.

Serum uromodulin is associated with the severity of clinicopathological findings in ANCA-associated glomerulonephritis

Background

Uromodulin (UMOD), also known as Tamm-Horsfall protein, is a kidney-specific protein expressed by epithelial cells lining the thick ascending limb of the loop of Henle. In the current study, we aimed to clarify the clinical significance of UMOD in ANCA-associated glomerulonephritis (AAG).

Materials and methods

Sixty-one biopsy-proven AAG patients were included in this study. UMOD was measured using ELISA. The relationships between serum UMOD (sUMOD) levels and various clinicopathological findings were evaluated.

Results

AAG was classified into four categories (focal, crescentic, mixed, and sclerotic). In addition, tubulointerstitial lesions were classified as mild, moderate, and severe. The levels of sUMOD and urinary UMOD (uUMOD) were correlated with each other. A negative correlation between sUMOD levels and serum Cr levels, and positive correlation between sUMOD levels and eGFR were found. Patients in the high sUMOD group were associated with low serum Cr levels, focal classification, and mild tubulointerstitial injury compared to the low sUMOD group. Comparing the characteristics among histopathological classes, patients in the focal class had the best renal function and the highest levels of uUMOD/Cr and sUMOD. The focal class had significantly better renal survival compared with the severe histopathological classes (crescentic, mixed, and sclerotic). In univariate logistic regression analyses, prognostic factors for severe histopathological classes were low uUMOD/Cr, high serum Cr, and low sUMOD. Multivariate analyses revealed that low sUMOD predicted severe histopathological classes independent of serum Cr. The mean levels of sUMOD were significantly different between the focal class and severe histopathological classes, with a sensitivity of 70.6% and specificity of 90.0% (cut-off 143 ng/ml, AUC 0.80) by ROC curves.

Conclusion

Low sUMOD levels were associated with severe clinicopathological findings and might be considered as a risk factor for end stage renal disease in AAG.

Serum uromodulin as a marker of kidney graft function*

Serum uromodulin (sURO) was recently found as a sensitive tubular marker in early chronic kidney disease stages. Thus far, mainly early uromodulin urinary excretion was tested in kidney recipients. The aim of our study was to conduct a long-lastinlong-term assessment of sURO in kidney graft function monitoring. Forty-one stable kidney recipients (aged 47 (13.7)) were studied around the 3^rd month (3m) and the 2^nd year (2y) after kidney transplantation. Sera were tested for sURO, creatinine and tacrolimus levels. Kidney biopsy was scored according to revised Banff 97 classification. sURO level (mean 66.06ng/ml at 3m; 77.81 at 2y) increased borderline significantly (P = 0.051) in time and significantly correlated with eGFR (3m RS = 0.46; 2y RS = 0.58), creatinine levels (RS respectively –0.55 and –0.56) and donor age (3m Rs = –0.33; 2y RS = –0.41). We observed borderline correlations between sURO and Banff biopsy scoring: 3m-sURO with arteriolar hyalinosis-ah (RS = –0.3, P = 0.06) and 2y-sURO with peritubular capillaritis-ptc (RS = 0.45, P = 0.07). Correlations of sURO with 3m tacrolimus levels (Rs = 0.3, P = 0.08) were borderline, however patients with CNI toxicity lesions in biopsy had sURO significantly lower (mean 3m-sURO 52.7 vs 83.1 ng/ml; 2y-sURO 61.9 vs 98.1 ng/ml). sURO can reflect kidney graft quality and function. sURO correlated with ptc, which is considered to be an early marker of a chronic antibody-mediated graft injury. Tacrolimus doesn’t influence sURO levels directly, but sURO is lower in patients with toxic kidney injury in biopsy.

Serum Uromodulin: A Biomarker of Long-Term Kidney Allograft Failure

BACKGROUND

Uromodulin is a kidney-derived glycoprotein and putative tubular function index. Lower serum uromodulin was recently associated with increased risk for kidney allograft failure in a preliminary, longitudinal single-center -European study involving 91 kidney transplant recipients (KTRs).

METHODS

The Folic Acid for Vascular Outcome Reduction in Transplantation (FAVORIT) trial is a completed, large, multiethnic controlled clinical trial cohort, which studied chronic, stable KTRs. We conducted a case cohort analysis using a randomly selected subset of patients (random subcohort, n = 433), and all individuals who developed kidney allograft failure (cases, n = 226) during follow-up. Serum uromodulin was determined in this total of n = 613 FAVORIT trial participants at randomization. Death-censored kidney allograft failure was the study outcome.

RESULTS

The 226 kidney allograft failures occurred during a median surveillance of 3.2 years. Unadjusted, weighted Cox proportional hazards modeling revealed that lower serum uromodulin, tertile 1 vs. tertile 3, was associated with a threefold greater risk for kidney allograft failure (hazards ratio [HR], 95% CI 3.20 [2.05-5.01]). This association was attenuated but persisted at twofold greater risk for allograft failure, after adjustment for age, sex, smoking, allograft type and vintage, prevalent diabetes mellitus and cardiovascular disease (CVD), total/high-density lipoprotein cholesterol ratio, systolic blood pressure, estimated glomerular filtration rate, and natural log urinary albumin/creatinine: HR 2.00, 95% CI (1.06-3.77).

CONCLUSIONS

Lower serum uromodulin, a possible indicator of less well-preserved renal tubular function, remained associated with greater risk for kidney allograft failure, after adjustment for major, established clinical kidney allograft failure and CVD risk factors, in a large, multiethnic cohort of long-term, stable KTRs.

Hypothesis: Potential Utility of Serum and Urine Uromodulin Measurement in Kidney Transplant Recipients?

Seventy years after its discovery, studies of the myriad properties, and potential disease associations of uromodulin are now burgeoning. Although normative ranges for serum/plasma uromodulin concentrations were established over 30 years ago, their external validation occurred only in very recent, larger studies. As tubular function indices, serum and urinary uromodulin may be more sensitive indicators of kidney graft dysfunction undetected by glomerular filtration markers, or proteinuria. Moreover, 2 sizable, just published longitudinal reports revealed that lower serum uromodulin levels were associated with cardiovascular disease (CVD) outcomes, total mortality, and infectious disease deaths, in patients with known or suspected coronary heart disease. Preliminary longitudinal studies have reported that reduced levels of plasma or serum uromodulin were linked to progression to end-stage renal disease in chronic kidney disease patients, and graft failure in kidney transplant recipients (KTRs). Conflicting data on the associations, or lack thereof, between lower urinary uromodulin concentrations and accelerated loss of renal function, or renal failure, in nontransplant chronic kidney disease patients, are perhaps due, in part, to analytical limitations in determining urine uromodulin. Potential longitudinal associations between serum and urinary uromodulin concentrations, and CVD outcomes, graft failure, and all-cause mortality, await validation in large, diverse cohorts of chronic KTRs. Taking advantage of an efficient case-cohort design scheme, we demonstrate how the completed FAVORIT clinical trial cohort might be ideally suited to evaluate these associations. Using available case-cohort sample data, statistical power simulations are provided to detect relative risk estimates of 1.50 for CVD (n = 309 events), 1.56 for graft failure (n = 223 events) or 1.50 for death from any cause (n = 320 events), comparing values below the median, to values equal to or above the median for serum uromodulin values. Edifying data such as these would advance our understanding of the hypothetical utility of uromodulin measurement in KTRs considerably.

Uromodulin: from physiology to rare and complex kidney disorders

Uromodulin (also known as Tamm-Horsfall protein) is exclusively produced in the kidney and is the most abundant protein in normal urine. The function of uromodulin remains elusive, but the available data suggest that this protein might regulate salt transport, protect against urinary tract infection and kidney stones, and have roles in kidney injury and innate immunity. Interest in uromodulin was boosted by genetic studies that reported involvement of the UMOD gene, which encodes uromodulin, in a spectrum of rare and common kidney diseases. Rare mutations in UMOD cause autosomal dominant tubulointerstitial kidney disease (ADTKD), which leads to chronic kidney disease (CKD). Moreover, genome-wide association studies have identified common variants in UMOD that are strongly associated with risk of CKD and also with hypertension and kidney stones in the general population. These findings have opened up a new field of kidney research. In this Review we summarize biochemical, physiological, genetic and pathological insights into the roles of uromodulin; the mechanisms by which UMOD mutations cause ADTKD, and the association of common UMOD variants with complex disorders.