Epidemiology of uromodulin-associated kidney disease - results from a nation-wide survey

The Pathophysiology of Inherited Renal Cystic Diseases

Renal cystic diseases (RCDs) can arise from utero to early adulthood and present with a variety of symptoms including renal, hepatic, and cardiovascular manifestations. It is well known that common RCDs such as autosomal polycystic kidney disease and autosomal recessive kidney disease are linked to genes such as PKD1 and PKHD1, respectively. However, it is important to investigate the genetic pathophysiology of how these gene mutations lead to clinical symptoms and include some of the less-studied RCDs, such as autosomal dominant tubulointerstitial kidney disease, multicystic dysplastic kidney, Zellweger syndrome, calyceal diverticula, and more. We plan to take a thorough look into the genetic involvement and clinical sequalae of a number of RCDs with the goal of helping to guide diagnosis, counseling, and treatment.

Autosomal dominant tubulointerstitial kidney disease: A review

The clinical characteristics of autosomal dominant tubulointerstitial kidney disease (ADTKD) include bland urinary sediment, slowly progressive chronic kidney disease (CKD) with many patients reaching end stage renal disease (ESRD) between age 20 and 70 years, and autosomal dominant inheritance. Due to advances in genetic diagnosis, ADTKD is becoming increasingly recognized as a cause of CKD. Pathogenic variants in UMOD, MUC1, and REN are the most common causes of ADTKD. ADTKD-UMOD is also associated with hyperuricemia and gout. ADTKD-REN often presents in childhood with mild hypotension, CKD, hyperkalemia, acidosis, and anemia. ADTKD-MUC1 patients present only with CKD. This review describes the pathophysiology, genetics, clinical manifestation, and diagnosis for ADTKD, with an emphasis on genetic testing and genetic counseling suggestions for patients.

Chronic Kidney Disease of Undetermined Etiology around the World

BACKGROUND

Epidemics of chronic kidney disease of uncertain etiology (CKDu) are occurring on the Pacific coast of Central America, in Sri Lankan and Indian agricultural communities, and in other hotspots around the world. CKDu primarily affects male agricultural workers, and traditional risk factors such as diabetes and hypertension are not involved in the pathogenesis. Although a causal factor has not yet been identified, culprits include repeated volume depletion-induced kidney injury, as well as exposure to agrichemicals, heavy metals and nephrotoxins contained in drugs, beverages, and traditional medications. Multiple risk factors may interact in a synergistic fashion thus resulting in chronic kidney damage. The absence of undefined protective factors may amplify the risk.

SUMMARY

This review focuses on the current understanding of CKDu by analyzing epidemiology, potential risk factors, and clinical and pathological features as well as geographical peculiarities of each disease. We also focus our attention on the etiology of these conditions in which multiple factors may synergistically contribute to the development and progression of the disease. The last part of the manuscript is dedicated to the research agenda and practical recommendations. Key Messages: Since renal replacement therapy is not extensively available in areas where CKDu is widespread, prevention by avoiding all known potential risk factors is crucial. Innovative healthcare solutions and social policies in endemic areas along with collaborative clinical research projects are needed to better identify factors involved in disease promotion and progression.

Autosomal dominant tubulointerstitial kidney disease (ADTKD) in Ireland

Introduction: Autosomal dominant tubulointerstitial kidney disease (ADTKD) is a rare genetic cause of renal impairment resulting from mutations in the MUC1, UMOD, HNF1B, REN, and SEC61A1 genes. Neither the national or global prevalence of these diseases has been determined. We aimed to establish a database of patients with ADTKD in Ireland and report the clinical and genetic characteristics of these families.

Methods: We identified patients via the Irish Kidney Gene Project and referral to the national renal genetics clinic in Beaumont Hospital who met the clinical criteria for ADTKD (chronic kidney disease, bland urinary sediment, and autosomal dominant inheritance). Eligible patients were then invited to undergo genetic testing by a variety of methods including panel-based testing, whole exome sequencing and, in five families who met the criteria for diagnosis of ADTKD but were negative for causal genetic mutations, we analyzed urinary cell smears for the presence of MUC1fs protein.

Results: We studied 54 individuals from 16 families. We identified mutations in the MUC1 gene in three families, UMOD in five families, HNF1beta in two families, and the presence of abnormal MUC1 protein in urine smears in three families (one of which was previously known to carry the genetic mutation). We were unable to identify a mutation in 4 families (3 of whom also tested negative for urinary MUC1fs).

Conclusions: There are 4443 people with ESRD in Ireland, 24 of whom are members of the cohort described herein. We observe that ADTKD represents at least 0.54% of Irish ESRD patients.

Autosomal dominant tubulointerstitial kidney disease

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is a recently defined entity that includes rare kidney diseases characterized by tubular damage and interstitial fibrosis in the absence of glomerular lesions, with inescapable progression to end-stage renal disease. These diseases have long been neglected and under-recognized, in part due to confusing and inconsistent terminology. The introduction of a gene-based, unifying terminology led to the identification of an increasing number of cases, with recent data suggesting that ADTKD is one of the more common monogenic kidney diseases after autosomal dominant polycystic kidney disease, accounting for ~5% of monogenic disorders causing chronic kidney disease. ADTKD is caused by mutations in at least five different genes, including UMOD, MUC1, REN, HNF1B and, more rarely, SEC61A1. These genes encode various proteins with renal and extra-renal functions. The mundane clinical characteristics and lack of appreciation of family history often result in a failure to diagnose ADTKD. This Primer highlights the different types of ADTKD and discusses the distinct genetic and clinical features as well as the underlying mechanisms.

Outcomes of patient self-referral for the diagnosis of several rare inherited kidney diseases

Purpose

To evaluate self-referral from the Internet for genetic diagnosis of several rare inherited kidney diseases.

Methods

Retrospective study from 1996–2017 analyzing data from an academic referral center specializing in autosomal dominant tubulo-interstitial kidney disease (ADTKD). Individuals were referred by academic health care providers (HCPs) non-academic HCPs, or directly by patients/families.

Results

Over 21 years, there were 665 referrals, with 176(27%) directly from families, 269(40%) from academic HCPs, and 220(33%) from non-academic HCPs. 42(24%) of direct family referrals had positive genetic testing vs 73(27%) of families from academic HCPs and 55(25%) from non-academic HCPs (P=.72). 99% of direct family contacts were white and resided in zip code locations with a mean median income of $77,316±34,014 vs. US median income $49,445.

Conclusions

Undiagnosed families with Internet access bypassed their physicians and established direct contact with an academic center specializing in inherited kidney disease to achieve a diagnosis. Twenty-five per cent of all families diagnosed with ADTKD were the result of direct family referral and would otherwise have been un-diagnosed. If patients suspect a rare disorder that is un-diagnosed by their physicians, actively pursuing self-diagnosis using the Internet can be successful. Centers interested in rare disorders should consider improving direct access to families.

Uromodulin-related autosomal-dominant tubulointerstitial kidney disease-pathogenetic insights based on a case

Uromodulin-related autosomal-dominant tubulointerstitial kidney disease (ADTKD-UMOD) is a rare monogenic disorder that is characterized by tubulointerstitial fibrosis and progression of kidney function loss, and may progress to end-stage renal disease. It is usually accompanied by hyperuricaemia and gout. Mutations in the uromodulin gene (UMOD) resulting in malfunctioning of UMOD are known to be the cause of ADTKD-UMOD, which is assumed to be an endoplasmatic reticulum (ER) storage disease. As a case vignette, we report a 29-year-old female with a suspicious family history of chronic kidney disease presenting with progressive loss of renal function, hyperuricaemia and frequent urinary tract infections. Urinary tract infections and pyelonephritides may represent a clinical feature of uromodulin malfunction as it plays a protective role against urinary tract infections despite only sporadic data on this topic. ADTKD-UMOD was diagnosed after genetic testing revealing a missense mutation in the UMOD gene. Light microscopy showed excessive tubular interstitial fibrosis and tubular atrophy together with signs of glomerular sclerosis. Electron microscopic findings could identify electron dense storage deposits in the ER of tubular epithelial cells of the thick ascending loop. Immunohistological staining with KDEL (lysine, aspartic acid, glutamic acid, leucine) showed positivity in the tubular cells, which likely represents ER expansion upon accumulation of misfolded UMOD which could trigger the unfolded protein response and ER stress. This review highlights pathophysiological mechanisms that are subject to ADTKD-UMOD.

Autosomal dominant tubulointerstitial kidney disease-UMOD is the most frequent non polycystic genetic kidney disease

Background

Autosomal dominant tubulointerstitial kidney disease (ADTKD) caused by mutations in the UMOD gene (ADTKD-UMOD) is considered rare and often remains unrecognised. We aimed to establish the prevalence of genetic kidney diseases, ADTKD and ADTKD-UMOD in adult chronic kidney disease (CKD) patients, and to investigate characteristic features.

Methods

We sent questionnaires on family history to all patients with CKD stages 3–5 in our tertiary renal centre to identify patients with inherited renal disease. Details on clinical and family history were obtained from patient interviews and clinical records. Sanger sequencing of the UMOD gene was performed from blood or saliva samples.

Results

2027 of 3770 sent questionnaires were returned. 459 patients reported a family history, which was consistent with inherited kidney disease in 217 patients. 182 non-responders with inherited kidney diseases were identified through a database search. Of these 399 individuals, 252 had autosomal dominant polycystic kidney disease (ADPKD), 28 had ADTKD, 25 had Alports, and 44 were unknown, resulting in 11% of CKD 3–5 patients and 19% of end-stage renal disease patients with genetic kidney diseases. Of the unknown, 40 were genotyped, of whom 31 had findings consistent with ADTKD. 30% of unknowns and 39% of unknowns with ADTKD had UMOD mutations. Altogether, 35 individuals from 18 families were found to have ten distinct UMOD mutations (three novel), making up 1% of patients with CKD 3–5, 2% of patients with end-stage renal disease, 9% of inherited kidney diseases and 56% with ADTKD. ADTKD-UMOD was the most common genetic kidney disease after ADPKD with a population prevalence of 9 per million. Less proteinuria and haematuria, but not hyperuricaemia or gout were predictive of ADTKD-UMOD. The main limitations of the study are the single-centre design and a predominantly Caucasian population.

Conclusions

The prevalence of genetic kidney diseases and ADTKD-UMOD is significantly higher than previously described. Clinical features poorly predicted ADTKD-UMOD, highlighting the need for genetic testing guided by family history alone.

Electronic supplementary material

The online version of this article (10.1186/s12882-018-1107-y) contains supplementary material, which is available to authorized users.

Identification of a novel UMOD mutation (c.163G>A) in a Brazilian family with autosomal dominant tubulointerstitial kidney disease

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is characterized by autosomal dominant inheritance, progressive chronic kidney disease, and a bland urinary sediment. ADTKD is most commonly caused by mutations in the UMOD gene encoding uromodulin (ADTKD-UMOD). We herein report the first confirmed case of a multi-generational Brazilian family with ADTKD-UMOD, caused by a novel heterozygous mutation (c.163G>A, GGC→AGC, p.Gly55Ser) in the UMOD gene. Of 41 family members, 22 underwent genetic analysis, with 11 individuals found to have this mutation. Three affected individuals underwent hemodialysis, one peritoneal dialysis, and one patient received a kidney transplant from a family member later found to be genetically affected. Several younger individuals affected with the mutation were also identified. Clinical characteristics included a bland urinary sediment in all tested individuals and a kidney biopsy in one individual showing tubulointerstitial fibrosis. Unlike most other reported families with ADTKD-UMOD, neither gout nor hyperuricemia was found in affected individuals. In summary, we report a novel UMOD mutation in a Brazilian family with 11 affected members, and we discuss the importance of performing genetic testing in families with inherited kidney disease of unknown cause.

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.

From juvenile hyperuricaemia to dysfunctional uromodulin: an ongoing metamorphosis

Familial juvenile hyperuricaemic nephropathy (FJHN) is a diagnosis that is easily missed. It has taken a long time to clarify the pathophysiology and prevalence of this disease entity which has been shown to be genetically identical to medullary cystic kidney disease (MCKD) type II. The initial suspicion that uric acid was the noxious agent has been replaced by the recognition that a mutant uromodulin (UMOD) is the real culprit-although the exact mechanisms of pathogenicity remain uncertain. The mutation has been traced to the UMOD gene in chromosome 16. The disease is characterised by the classic triad of autosomal dominant inheritance, progressive renal failure beginning in the third to fifth decade of life and gout. Phenotypically similar but genotypically distinct entities have been described over the last 10 years, making a clinical diagnosis difficult. These include mutations in the renin, hepatocyte nuclear factor 1-β and mucin 1 genes. UMOD-associated kidney disease has been proposed as a logical diagnostic label to replace FJHN, but given all these other mutations, an over-arching diagnostic term of 'autosomal dominant tubulointerstitial kidney disease' (ADTKD) has been recently adopted. Allopurinol has been suggested as a therapeutic agent, but unfortunately this was based on non-randomised uncontrolled trials with small patient numbers.

Familial juvenile hyperuricemic nephropathy as rare cause of dialysis-dependent chronic kidney disease-a series of cases in two families

Hyperuricemia is a common symptom in adult population. It usually accompanies the chronic kidney disease. Less frequently, it is a primary phenomenon causing later serious clinical consequences. Familial juvenile hyperuricemic nephropathy (FJHN) is one of the hereditary conditions associated with high levels of serum uric acid and leading to dialysis in young adult age. It results from mutation in the UMOD gene, encoding the uromodulin protein, that is, Tamm-Horsfall protein. The aim of this paper was to present two families (7 affected members) with FJHN, in whom standard nephrological diagnostics did not provide clear cause of dialysis-dependent chronic kidney disease, until genetic testing was performed.

Autosomal dominant tubulointerstitial kidney disease caused by uromodulin mutations: seek and you will find

BACKGROUND

Uromodulin (UMOD)-associated kidney disease belongs to the group of autosomal dominant interstitial kidney diseases and is caused by mutations in the UMOD gene. Affected patients present with hyperuricemia, gout, and progressive renal failure. The disease is thought to be very rare but is probably underdiagnosed.

METHODS

Two index patients from two families with tubulointerstitial nephropathy and hyperuricemia were examined, including blood and urine chemistry, ultrasound, and mutation analysis of the UMOD gene. In addition, other available family members were studied.

RESULTS

In a 46-year-old female patient with a fractional excretion of uric acid of 3 %, analysis of the UMOD gene revealed a p.W202S missense mutation. The same mutation was found in her 72-year-old father, who suffers from gout and end-stage renal disease. The second index patient was a 47-year-old female with chronic kidney disease and gout for more than 10 years. Her fractional uric acid excretion was 3.5 %. Genetic analysis identified a novel p.H250Q UMOD mutation that was also present in her 12-year-old son, who had normal renal function and uric acid levels.

CONCLUSION

In patients suffering from chronic tubulointerstitial nephropathy, hyperuricemia, and a low fractional excretion of uric acid mutation, analysis of the UMOD gene should be performed to diagnose UMOD-associated kidney disease.

Hints to the diagnosis of uromodulin kidney disease

Background

Uromodulin kidney disease (UKD) is an inherited kidney disease caused by a uromodulin (UMOD) gene mutation. The UMOD gene encodes the Tamm–Horsfall protein (THP), which is the most abundant protein in healthy human urine. Because of its rarity, the incidence of UKD has not been fully elucidated. The purpose of the present study is to clarify the frequency of UKD among patients who underwent renal biopsy.

Methods

Immunostaining for THP was performed for patients <50 years of age with renal insufficiency and hyperuricemia without overt urinalysis abnormality from renal biopsy databases. Serum and urinary THP concentrations were evaluated in available individuals.

Results

Fifteen patients were selected for immunostaining from a total of 3787 patients. In three independent patients, abnormal THP accumulation in renal tubular cells was observed. A novel missense A247P UMOD mutation was detected in two of the three patients, including one having a typical family history of familial juvenile hyperuricemic nephropathy. Serum and urinary THP concentrations of all available patients with UMOD A247P mutation were significantly lower than those of controls.

Conclusions

In the present study, UKD was detected in <1 in 1000 subjects who underwent renal biopsies. However, in subjects meeting all of the above criteria, abnormal THP accumulation was detected in 20% (3/15), suggesting that renal biopsy with immunostaining for THP is a good tool for diagnosing UKD. Also, low serum THP concentration detected in the present subjects might be a good diagnostic marker or important in understanding the pathogenesis of UKD.

The therapeutic effects of 4-phenylbutyric acid in maintaining proteostasis

Recently, there has been an increasing amount of literature published on the effects of 4-phenylbutyric acid (4-PBA) in various biological systems. 4-PBA is currently used clinically to treat urea cycle disorders under the trade name Buphenyl. Recent studies however have explored 4-PBA in the context of a low weight molecular weight chemical chaperone. Its properties as a chemical chaperone prevent misfolded protein aggregation and alleviate endoplasmic reticulum (ER) stress. As the ER is responsible for folding proteins targeted for use in membranes or secreted out of the cell, failure of maintaining adequate ER homeostasis may lead to protein misfolding and subsequent cell and organ pathology. Accumulation of misfolded proteins within the ER activates the unfolded protein response (UPR), a molecular repair response. The activation of the UPR aims to restore ER and cellular proteostasis by regulating the rate of synthesis of newly formed proteins as well as initiating molecular programs aimed to help fold or degrade misfolded proteins. If proteostasis is not restored, the UPR may initiate pro-apoptotic pathways. It is suggested that 4-PBA may help fold proteins in the ER, attenuating the activation of the UPR, and thus potentially alleviating various pathologies. This review discusses the biomedical research exploring the potential therapeutic effects of 4-PBA in various in vitro and in vivo model systems and clinical trials, while also commenting on the possible mechanisms of action.

Unexpectedly high prevalence of rare genetic disorders in kidney transplant recipients with an unknown causal nephropathy

BACKGROUND

Patients with a rare genetic disease may receive renal transplantation (KTx) without a correct diagnosis of causal nephropathy and therefore develop unexpected and even severe complications. The aim of the study was to describe the cases of rare genetic disorders diagnosed after KTx, in order to draw clinical lessons for the transplant physician.

METHODS

We retrospectively assessed all patients who had received a diagnosis of a rare genetic disorder after KTx.

RESULTS

In our center, more than 30% (278/911) of kidney transplant (KTx) recipients were diagnosed with a causal nephropathy: Prevalence of rare genetic disorders in this group was 4.32% (12/278), including 2,8-dihydroxyadeninuria (2,8-DHA) disease (n = 2), HNF-1B-associated nephropathy (n = 2), UMOD-related nephropathy (n = 5), Fabry disease (n = 1), INF2 focal segmental glomerulosclerosis (n = 1), and Senior-Løken syndrome (n = 1). 2,8-DHA nephropathy relapsed in both patients causing an acute renal failure and jeopardizing the graft.

CONCLUSIONS

Kidney transplant recipients without a diagnosis of causal nephropathy appear to be a selected population in which rare genetic diseases might be more common than expected. As even a belated diagnosis after KTx can have a significant impact on graft and patient survival and on other family members, this possibility should be evaluated in KTx recipients without a known causal nephropathy.

Association between genotype and phenotype in uromodulin-associated kidney disease

BACKGROUND AND OBJECTIVES

Uromodulin-associated kidney disease (UAKD) is an autosomal dominant disease caused by uromodulin (UMOD) gene mutations. This study explored genotype-phenotype correlations by examining the relationship between the type of UMOD mutation and the age at onset of ESRD.

DESIGN, SETTING, PARTICIPANTS & MEASUREMENTS

Extensive bibliographic research was used to ascertain patient-level data of all patients with UAKD published up to October 2011. Data included sex; ages at onset of hyperuricemia, gout, and ESRD; and UMOD genotype. Kaplan-Meier analysis and Cox proportional hazards models fitted with shared gamma frailty terms to adjust for within-family correlations were used to model time to event.

RESULTS

Thirty-one peer-reviewed publications reporting on 202 patients from 74 families with 59 different UMOD mutations were included. Median ages at onset of hyperuricemia, gout, and ESRD were 24, 40, and 56 years, respectively. Men developed gout and ESRD significantly earlier than did women (age at ESRD was 50 years for men and 60 for women; P=0.04, shared frailty model). Median ages at ESRD development were lowest with Cys77Tyr (37.5 years) and highest with Gln316Pro (65.5 years) UMOD mutations. Onset of ESRD was significantly earlier with UMOD mutations located within the epidermal growth factor domains 2 and 3 (range, 45-52 years; P<0.01 and 0.04, respectively) compared with the cysteine-rich domains (range, 60-65 years; by shared frailty model).

CONCLUSIONS

The UMOD genotype is related to the clinical phenotype of UAKD. This finding may assist in counseling of patients.