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

Hidden genetics behind glomerular scars: an opportunity to understand the heterogeneity of focal segmental glomerulosclerosis?

Focal segmental glomerulosclerosis (FSGS) is a complex disease which describes different kinds of kidney defects, not exclusively linked with podocyte defects. Since nephrin mutation was first described in association with early-onset nephrotic syndrome (NS), many advancements have been made in understanding genetic patterns associated with FSGS. New genetic causes of FSGS have been discovered, displaying unexpected genotypes, and recognizing possible site of damage. Many recent large-scale sequencing analyses on patients affected by idiopathic chronic kidney disease (CKD), kidney failure (KF) of unknown origin, or classified as FSGS, have revealed collagen alpha IV genes, as one of the most frequent sites of pathogenic mutations. Also, recent interest in complex and systemic lysosomal storage diseases, such as Fabry disease, has highlighted GLA mutations as possible causes of FSGS. Tubulointerstitial disease, recently classified by KDIGO based on genetic subtypes, when associated with UMOD variants, may phenotypically gain FSGS features, as well as ciliopathy genes or others, otherwise leading to completely different phenotypes, but found carrying pathogenic variants with associated FSGS phenotype. Thus, glomerulosclerosis may conceal different heterogeneous conditions. When a kidney biopsy is performed, the principal objective is to provide an accurate diagnosis. The broad spectrum of phenotypic expression and genetic complexity is demonstrating that a combined path of management needs to be applied. Genetic investigation should not be reserved only to selected cases, but rather part of medical management, integrating with clinical and renal pathology records. FSGS heterogeneity should be interpreted as an interesting opportunity to discover new pathways of CKD, requiring prompt genotype-phenotype correlation. In this review, we aim to highlight how FSGS represents a peculiar kidney condition, demanding multidisciplinary management, and in which genetic analysis may solve some otherwise unrevealed idiopathic cases. Unfortunately there is not a uniform correlation between specific mutations and FSGS morphological classes, as the same variants may be identified in familial cases or sporadic FSGS/NS or manifest a variable spectrum of the same disease. These non-specific features make diagnosis challenging. The complexity of FSGS genotypes requires new directions. Old morphological classification does not provide much information about the responsible cause of disease and misdiagnoses may expose patients to immunosuppressive therapy side effects, mistaken genetic counseling, and misguided kidney transplant programs.

What Is Hidden in Patients with Unknown Nephropathy? Genetic Screening Could Be the Missing Link in Kidney Transplantation Diagnosis and Management

Between 15-20% of patients with end stage renal disease (ESRD) do not know the cause of the primary kidney disease and can develop complications after kidney transplantation. We performed a genetic screening in 300 patients with kidney transplantation, or undiagnosed primary renal disease, in order to identify the primary disease cause and discriminate between overlapping phenotypes. We used a custom-made panel for next-generation sequencing (Agilent technology, Santa Clara, CA, USA), including genes associated with Fabry disease, podocytopaties, complement-mediated nephropathies and Alport syndrome-related diseases. We detected candidate diagnostic variants in genes associated with nephrotic syndrome and Focal Segmental Glomerulosclerosis (FSGS) in 29 out of 300 patients, solving about 10% of the probands. We also identified the same genetic cause of the disease (PAX2: c.1266dupC) in three family members with different clinical diagnoses. Interestingly we also found one female patient carrying a novel missense variant, c.1259C>A (p.Thr420Lys), in the GLA gene not previously associated with Fabry disease, which is in silico defined as a likely pathogenic and destabilizing, and associated with a mild alteration in GLA enzymatic activity. The identification of the specific genetic background may provide an opportunity to evaluate the risk of recurrence of the primary disease, especially among patient candidates living with a donor kidney transplant.

Interventions to support adolescents and young adults with the healthcare transition from paediatric to adult nephrology health services: A scoping review protocol

Background

Due to technological advancements and improved medical management of adolescents and young adults (AYAs) living with renal disease, there has been an exponential increase noted in the number of patients advancing from the paediatric to the adult nephrology healthcare setting. Subsequently, more AYAs are required to undergo the process of healthcare transition from paediatric to adult healthcare services. This process can be a challenging period for young people and families and is often associated with a decline in physical and psychosocial health outcomes of AYAs with renal disorders. To ensure a successful transition, AYAs must develop the ability to manage their renal condition, including the medical and psychosocial aspects of their condition, independently. Despite significant research into the transition from paediatric to adult healthcare for this unique patient cohort, the transition period remains a challenge at times. This scoping review aims to map, explore, and understand the interventions that are currently available to offer positive perceptions and experiences of transition for both AYAs living with renal disorders and their families.

Methods

A systematic literature search will be conducted of PubMed, PsycInfo, CINAHL, ASSIA, EMBASE and Web of Science databases from the year 2000 to present. Two independent reviewers will screen the peer-reviewed literature obtained and assess them against the inclusion criteria to determine their inclusion eligibility. Data will be extracted and synthesised using a template refined by the authors. The scoping review will be undertaken in accordance with PRISMA-ScR guidelines. Data will undergo a formal critical appraisal using recognised appraisal tools.

Conclusions

Through mapping this knowledge, the scoping review will aim to identify interventions that are currently available and identify gaps within the literature. This evidence may support the development of transitional care interventions in the future, promote patient satisfaction, and improve patient outcome measures and experiences.

Interventions to support adolescents and young adults with the healthcare transition from paediatric to adult nephrology health services: A scoping review protocol

Background: Due to technological advancements and improved medical management of adolescents and young adults (AYAs) living with renal disease, there has been an exponential increase noted in the number of patients advancing from the paediatric to adult nephrology healthcare setting. Subsequently, more AYAs are required to undergo the process of healthcare transition from paediatric to adult healthcare services. This process is often a challenging period for young people and families and is often associated with a decline in physical and psychosocial health outcomes of AYAs with renal disorders. To ensure a successful transition, AYAs must develop the ability to manage their renal condition, including the medical and psychosocial aspects of their condition, independently. Despite significant research into the transition from paediatric to adult healthcare for this unique patient cohort, the transition period remains a challenge. The scoping review will aim to map, explore, and understand the interventions that are currently available to offer positive perceptions and experiences of transition for both AYAs living with renal disorders and their families. Methods: A systematic literature search will be conducted of PubMed, PsycInfo, CINAHL, ASSIA, EMBASE and Web of Science databases from the year 2000 to present. Two independent reviewers will screen the title and abstracts of peer-reviewed literature obtained and assess them against the inclusion criteria to determine their inclusion eligibility. Data will be extracted and synthesised using a template refined by the authors. The scoping review will be undertaken in accordance with PRISMA-ScR guidelines. Data will undergo a formal critical appraisal using recognised appraisal tools. Conclusions: Through mapping this knowledge, the scoping review will aim to identify interventions that are currently available and identify gaps within the literature. This evidence may support the development of transitional care interventions in the future, promote patient satisfaction, and improve patient outcome measures and experiences.

A deficiência de adenina fosforibosiltransferase leva à disfunção do aloenxerto renal em receptores de transplante renal: uma revisão sistemática

Resumo Antecedentes: A deficiência de adenina fosforibosiltransferase (APRT) tem grandes implicações na sobrevida do enxerto em pacientes transplantados renais. Esta revisão sistemática investigou o padrão diagnóstico, a abordagem de tratamento e os desfechos do transplante renal entre pacientes transplantados renais com deficiência de adenina fosforibosiltransferase. Material e métodos: Os artigos que relatam sobre a enzima APRT e a disfunção do aloenxerto renal foram recuperados do PubMed/Medline, ScienceDirect, Biblioteca Cochrane e bancos de dados do Google Acadêmico. Utilizou-se a análise descritiva para extrair inferências. Resultados: Foram incluídos participantes que receberam 39 enxertos, a maioria dos quais provenientes de doadores vivos seguidos por doadores falecidos e doadores cadáveres. Foi relatado tempo de sobrevida do enxerto superior a 6 meses em 23 (76,7%) pacientes, enquanto outros 7 (23,3%) pacientes tiveram tempo de sobrevida do enxerto inferior a 6 meses. Apenas 4 (13,3%) pacientes apresentaram deficiência de APRT antes do transplante. Após acompanhamento, um terço dos pacientes, 10 (33,3%) apresentaram função do enxerto estável, 1 paciente teve perda do aloenxerto, 8 (26,6%) pacientes apresentaram função retardada do enxerto, enquanto os 11 (36,6%) pacientes restantes tiveram disfunção crônica do enxerto renal. Conclusões: A deficiência de APRT é uma causa subestimada e reversível de nefropatia cristalina que leva à disfunção do aloenxerto renal ou à perda total do aloenxerto. Os resultados deste estudo pedem a inclusão desta condição no diagnóstico diferencial de nefropatia cristalina, mesmo na ausência de um histórico de nefrolitíase.

Adenine phosphoribosyl transferase deficiency leads to renal allograft dysfunction in kidney transplant recipients: a systematic review

Background:

Adenine phosphoribosyl transferase (APRT) deficiency has great implications on graft survival in kidney transplant patients. This systematic review investigated the diagnostic pattern, treatment approach, and kidney transplant outcomes among kidney transplant patients with adenine phosphoribosyl transferase deficiency.

Material and methods:

Articles reporting the APRT enzyme deficiency and kidney allograft dysfunction were retrieved from PubMed/Medline, ScienceDirect, Cochrane library and Google scholar databases. Descriptive analysis was used to draw inferences.

Results:

The results from 20 selected studies covering 30 patients receiving 39 grafts had an average age of 46.37 years are presented. Graft survival time of more than 6 months was reported in 23 (76.7%) patients, while other 7 (23.3%) patients had graft survival time of less than 6 months. Only 4 (13.3%) patients had APRT deficiency before transplantation. After follow-up, one-third of the patients 10 (33.3%) had stable graft function, 1 patient had allograft loss, 8 (26.6%) patients had delayed graft function while the remaining 11 (36.6%) patients had chronic kidney graft dysfunction.

Conclusions:

APRT deficiency is an under-recognized, treatable condition that causes reversible crystalline nephropathy, leading to loss of allograft or allograft dysfunction. The study results showed that inclusion of genetic determination of APRT deficiency in the differential diagnosis of crystalline nephropathy, even in the absence of a history of nephrolithiasis, can improve renal outcomes and may improve allograft survival.

The frequency of rare and monogenic diseases in pediatric organ transplant recipients in Italy

Background

Rare diseases are chronic and life-threatening disorders affecting < 1 person every 2,000. For most of them, clinical symptoms and signs can be observed at birth or childhood. Approximately 80% of all rare diseases have a genetic background and most of them are monogenic conditions. In addition, while the majority of these diseases is still incurable, early diagnosis and specific treatment can improve patients’ quality of life. Transplantation is among the therapeutic options and represents the definitive treatment for end-stage organ failure, both in children and adults. The aim of this paper was to analyze, in a large cohort of Italian patients, the main rare genetic diseases that led to organ transplantation, specifically pointing the attention on the pediatric cohort.

Results

To the purpose of our analysis, we considered heart, lung, liver and kidney transplants included in the Transplant Registry (TR) of the Italian National Transplantation Center in the 2002–2019 timeframe. Overall, 49,404 recipients were enrolled in the cohort, 5.1% of whom in the pediatric age. For 40,909 (82.8%) transplant recipients, a disease diagnosis was available, of which 38,615 in the adult cohort, while 8,495 patients (17.2%) were undiagnosed. There were 128 disease categories, and of these, 117 were listed in the main rare disease databases. In the pediatric cohort, 2,294 (5.6%) patients had a disease diagnosis: of the 2,126 (92.7%) patients affected by a rare disease, 1,402 (61.1%) presented with a monogenic condition. As expected, the frequencies of pathologies leading to organ failure were different between the pediatric and the adult cohort. Moreover, the pediatric group was characterized, compared to the adult one, by an overall better survival of the graft at ten years after transplant, with the only exception of lung transplants. When comparing survival considering rare vs non-rare diseases or rare and monogenic vs rare non-monogenic conditions, no differences were highlighted for kidney and lung transplants, while rare diseases had a better survival in liver as opposed to heart transplants.

Conclusions

This work represents the first national survey analyzing the main genetic causes and frequencies of rare and/or monogenic diseases leading to organ failure and requiring transplantation both in adults and children.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02013-x.

Kidney Transplant Outcomes in Patients With Adenine Phosphoribosyltransferase Deficiency

BACKGROUND

Adenine phosphoribosyltransferase (APRT) deficiency is a rare, hereditary cause of kidney stones and chronic kidney disease (CKD) which is characterized by 2,8-dihydroxyadenine renal parenchymal crystal deposition. The aim of this study was to examine outcomes of kidney transplantation in APRT deficiency patients.

METHODS

Included were 13 patients in the APRT Deficiency Registry of the Rare Kidney Stone Consortium, 2 from Westmead Hospital in Sydney, Australia, and 2 from Necker Hospital in Paris, France. The CKD-EPI and CKiD equations were used to calculate glomerular filtration rate estimates. Allograft survival was analyzed employing the Kaplan-Meier method. The Wilcoxon-Mann-Whitney test was used to compare alllograft outcomes according to xanthine oxidoreductase (XOR) inhibitor treatment status at transplantation.

RESULTS

Seventeen patients (9 females) received 22 kidney transplants. Age at first transplantation was 47.2 (14.9-67.0) years. Ten patients received XOR inhibitor therapy pretransplant (11 allografts), while 8 patients did not receive such treatment before transplantation (11 allografts). Two-year allograft survival was 91% and 55% in the 2 groups, respectively (P = 0.16). The median (range) estimated glomerular filtration rate at 2 years posttransplant was 61.3 (24.0-90.0) mL/min/1.73 m when XOR inhibitor therapy was initiated before transplantation, and 16.2 (10.0-39.0) mL/min/1.73 m (P = 0.009) when such treatment was not administered pretransplant.

CONCLUSIONS

Kidney allograft outcomes are good in APRT deficiency patients beginning XOR inhibitor therapy pretransplant. Delay in such treatment is a major cause of premature graft loss in these patients. Increased awareness among clinicians is imperative, promoting early diagnosis of APRT deficiency and pharmacotherapy initiation before kidney transplantation.

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.

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.

Monoallelic Mutations to DNAJB11 Cause Atypical Autosomal-Dominant Polycystic Kidney Disease

Autosomal-dominant polycystic kidney disease (ADPKD) is characterized by the progressive development of kidney cysts, often resulting in end-stage renal disease (ESRD). This disorder is genetically heterogeneous with ∼7% of families genetically unresolved. We performed whole-exome sequencing (WES) in two multiplex ADPKD-like pedigrees, and we analyzed a further 591 genetically unresolved, phenotypically similar families by targeted next-generation sequencing of 65 candidate genes. WES identified a DNAJB11 missense variant (p.Pro54Arg) in two family members presenting with non-enlarged polycystic kidneys and a frameshifting change (c.166_167insTT) in a second family with small renal and liver cysts. DNAJB11 is a co-factor of BiP, a key chaperone in the endoplasmic reticulum controlling folding, trafficking, and degradation of secreted and membrane proteins. Five additional multigenerational families carrying DNAJB11 mutations were identified by the targeted analysis. The clinical phenotype was consistent in the 23 affected members, with non-enlarged cystic kidneys that often evolved to kidney atrophy; 7 subjects reached ESRD from 59 to 89 years. The lack of kidney enlargement, histologically evident interstitial fibrosis in non-cystic parenchyma, and recurring episodes of gout (one family) suggested partial phenotypic overlap with autosomal-dominant tubulointerstitial diseases (ADTKD). Characterization of DNAJB11-null cells and kidney samples from affected individuals revealed a pathogenesis associated with maturation and trafficking defects involving the ADPKD protein, PC1, and ADTKD proteins, such as UMOD. DNAJB11-associated disease is a phenotypic hybrid of ADPKD and ADTKD, characterized by normal-sized cystic kidneys and progressive interstitial fibrosis resulting in late-onset ESRD.

Genomic medicine for kidney disease

Technologies such as next-generation sequencing and chromosomal microarray have advanced the understanding of the molecular pathogenesis of a variety of renal disorders. Genetic findings are increasingly used to inform the clinical management of many nephropathies, enabling targeted disease surveillance, choice of therapy, and family counselling. Genetic analysis has excellent diagnostic utility in paediatric nephrology, as illustrated by sequencing studies of patients with congenital anomalies of the kidney and urinary tract and steroid-resistant nephrotic syndrome. Although additional investigation is needed, pilot studies suggest that genetic testing can also provide similar diagnostic insight among adult patients. Reaching a genetic diagnosis first involves choosing the appropriate testing modality, as guided by the clinical presentation of the patient and the number of potential genes associated with the suspected nephropathy. Genome-wide sequencing increases diagnostic sensitivity relative to targeted panels, but holds the challenges of identifying causal variants in the vast amount of data generated and interpreting secondary findings. In order to realize the promise of genomic medicine for kidney disease, many technical, logistical, and ethical questions that accompany the implementation of genetic testing in nephrology must be addressed. The creation of evidence-based guidelines for the utilization and implementation of genetic testing in nephrology will help to translate genetic knowledge into improved clinical outcomes for patients with kidney disease.

Screening for Fabry Disease in Kidney Disease: a Cross-Sectional Study in Males and Females

BACKGROUND/AIMS

Evaluate the prevalence of Fabry disease in men and women with kidney disease; and observe the presence and importance of the main signs and symptoms in patients with kidney disease.

METHODS

A cross-sectional analysis of secondary data from a multicenter project of Clinical and Epidemiological Analysis of Fabry Disease in 854 Dialysis Centers. A total of 36,442 patients underwent the questionnaire and algorithm; of them, 28,284 were discarded for not presenting signs and symptoms of Fabry disease, while the other 8,087 submitted to blood collection and analysis. All participants signed a Free and Informed Consent Form and a questionnaire was applied. The questionnaire data were analyzed using a computerized algorithm. This program/algorithm analyzes and separates patients into: discarded, patients unlikely to have Fabry disease; suspect, patients who submitted to blood collection. The blood of suspect patients was collected on filter paper for enzyme measurement and genetic testing. A descriptive data analysis was performed and the likelihood ratio was determined.

RESULTS

The general prevalence was 0.19% and after use of algorithm was 0.87%. Although more men were screened (59.3%), the prevalence was higher in women (65.1%). The most prevalent signs and symptoms were: heart disease (60.6%), decreased or lack of sweating (42.3%), heat and cold intolerance (28.2%), and pain crises spreading throughout the body (26.8%).

CONCLUSION

The prevalence was higher in women, and the most prevalent symptom was heart diseases.

Inverted formins: A subfamily of atypical formins

Formins are a family of regulators of actin and microtubule dynamics that are present in almost all eukaryotes. These proteins are involved in many cellular processes, including cytokinesis, stress fiber formation, and cell polarization. Here we review one subfamily of formins, the inverted formins. Inverted formins as a group break several formin stereotypes, having atypical biochemical properties and domain organization, and they have been linked to kidney disease and neuropathy in humans. In this review, we will explore recent research on members of the inverted formin sub-family in mammals, zebrafish, fruit flies, and worms.

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.

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.