Autosomal dominant mutation in the signal peptide of renin in a kindred with anemia, hyperuricemia, and CKD

Btg2 mutation induces renal injury and impairs blood pressure control in female rats

Hypertension (HTN) is a complex disease influenced by heritable genetic elements and environmental interactions. Dietary salt is among the most influential modifiable factors contributing to increased blood pressure (BP). It is well established that men and women develop BP impairment in different patterns and a recent emphasis has been placed on identifying mechanisms leading to the differences observed between the sexes in HTN development. The current work reported here builds on an extensive genetic mapping experiment which sought to identify genetic determinants of salt sensitive (SS) HTN using the Dahl SS rat. BTG anti-proliferation factor 2 (Btg2) was previously identified by our group as a candidate gene contributing to SS HTN in female rats. In the current study, Btg2 was mutated using TALEN targeted gene disruption on the SSBN congenic rat background. The Btg2 mutated rats exhibited impaired BP and proteinuria responses to a high salt diet compared to wild type rats. Differences in body weight, mutant pup viability, skeletal morphology, and adult nephron density suggest a potential role for Btg2 in developmental signaling pathways. Subsequent cell cycle gene expression assessment provides several additional signaling pathways that Btg2 may function through during salt handling in the kidney. The expression analysis also identified several potential upstream targets that can be explored to further isolate therapeutic approaches for SS HTN.

Phenylbutyrate rescues the transport defect of the Sec61α mutations V67G and T185A for renin

The human Sec61 complex is a widely distributed and abundant molecular machine. It resides in the membrane of the endoplasmic reticulum to channel two types of cargo: protein substrates and calcium ions. The SEC61A1 gene encodes for the pore-forming Sec61α subunit of the Sec61 complex. Despite their ubiquitous expression, the idiopathic SEC61A1 missense mutations p.V67G and p.T185A trigger a localized disease pattern diagnosed as autosomal dominant tubulointerstitial kidney disease (ADTKD-SEC61A1). Using cellular disease models for ADTKD-SEC61A1, we identified an impaired protein transport of the renal secretory protein renin and a reduced abundance of regulatory calcium transporters, including SERCA2. Treatment with the molecular chaperone phenylbutyrate reversed the defective protein transport of renin and the imbalanced calcium homeostasis. Signal peptide substitution experiments pointed at targeting sequences as the cause for the substrate-specific impairment of protein transport in the presence of the V67G or T185A mutations. Similarly, dominant mutations in the signal peptide of renin also cause ADTKD and point to impaired transport of this renal hormone as important pathogenic feature for ADTKD-SEC61A1 patients as well.

The Molecular Biodiversity of Protein Targeting and Protein Transport Related to the Endoplasmic Reticulum

Looking at the variety of the thousands of different polypeptides that have been focused on in the research on the endoplasmic reticulum from the last five decades taught us one humble lesson: no one size fits all. Cells use an impressive array of components to enable the safe transport of protein cargo from the cytosolic ribosomes to the endoplasmic reticulum. Safety during the transit is warranted by the interplay of cytosolic chaperones, membrane receptors, and protein translocases that together form functional networks and serve as protein targeting and translocation routes. While two targeting routes to the endoplasmic reticulum, SRP (signal recognition particle) and GET (guided entry of tail-anchored proteins), prefer targeting determinants at the N- and C-terminus of the cargo polypeptide, respectively, the recently discovered SND (SRP-independent) route seems to preferentially cater for cargos with non-generic targeting signals that are less hydrophobic or more distant from the termini. With an emphasis on targeting routes and protein translocases, we will discuss those functional networks that drive efficient protein topogenesis and shed light on their redundant and dynamic nature in health and disease.

Autosomal dominant tubulointerstitial kidney disease genotype and phenotype correlation in a Chinese cohort

Genes of UMOD, HNF1B, MUC1, REN and SEC61A1 were reported to be associated with autosomal dominant tubulointerstitial kidney disease (ADTKD). 48 probands and their family members (N = 27) were enrolled in this genetic screening study. A combination of methods was employed for comprehensive molecular analysis of both copy number variations (CNVs) and single nucleotide variants (SNVs). 35 probands were followed for years. The phenotype-genotype and genotype-outcome correlation were inferred from these datasets. In this cohort, 18 probands were diagnosed with ADTKD, according to Kidney Disease: Improving Global Outcomes (KDIGO) guideline. Moreover, 11 probands were diagnosed with ADTKD-UMOD, one with ADTKD-REN and one with ADTKD-HNF1B, based on molecularly confirmed pathogenic variants. The 11 UMOD variants were mainly located in codons 28 to 289 and half of the variants were found to change the cysteine amino acid. According to the follow-up data, suspected ADTKD individuals had a better prognosis compared to ADTKD individuals (p = 0.029). Individuals with a cysteine substitution in the UMOD gene appeared to have a better prognosis than individuals with other amino acid substitutions (p = 0.015).

An international cohort study of autosomal dominant tubulointerstitial kidney disease due to REN mutations identifies distinct clinical subtypes

There have been few clinical or scientific reports of autosomal dominant tubulointerstitial kidney disease due to REN mutations (ADTKD-REN), limiting characterization. To further study this, we formed an international cohort characterizing 111 individuals from 30 families with both clinical and laboratory findings. Sixty-nine individuals had a REN mutation in the signal peptide region (signal group), 27 in the prosegment (prosegment group), and 15 in the mature renin peptide (mature group). Signal group patients were most severely affected, presenting at a mean age of 19.7 years, with the prosegment group presenting at 22.4 years, and the mature group at 37 years. Anemia was present in childhood in 91% in the signal group, 69% prosegment, and none of the mature group. REN signal peptide mutations reduced hydrophobicity of the signal peptide, which is necessary for recognition and translocation across the endoplasmic reticulum, leading to aberrant delivery of preprorenin into the cytoplasm. REN mutations in the prosegment led to deposition of prorenin and renin in the endoplasmic reticulum-Golgi intermediate compartment and decreased prorenin secretion. Mutations in mature renin led to deposition of the mutant prorenin in the endoplasmic reticulum, similar to patients with ADTKD-UMOD, with a rate of progression to end stage kidney disease (63.6 years) that was significantly slower vs. the signal (53.1 years) and prosegment groups (50.8 years) (significant hazard ratio 0.367). Thus, clinical and laboratory studies revealed subtypes of ADTKD-REN that are pathophysiologically, diagnostically, and clinically distinct.

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 with Adult Onset due to a Novel Renin Mutation Mapping in the Mature Protein

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is a genetically heterogeneous renal disorder leading to progressive loss of renal function. ADTKD-REN is due to rare mutations in renin, all localized in the protein leader peptide and affecting its co-translational insertion in the endoplasmic reticulum (ER). Through exome sequencing in an adult-onset ADTKD family we identified a new renin variant, p.L381P, mapping in the mature protein. To assess its pathogenicity, we combined genetic data, computational and predictive analysis and functional studies. The L381P substitution affects an evolutionary conserved residue, co-segregates with renal disease, is not found in population databases and is predicted to be deleterious by in silico tools and by structural modelling. Expression of the L381P variant leads to its ER retention and induction of the Unfolded Protein Response in cell models and to defective pronephros development in zebrafish. Our work shows that REN mutations outside of renin leader peptide can cause ADTKD and delineates an adult form of ADTKD-REN, a condition which has usually its onset in childhood. This has implications for the molecular diagnosis and the estimated prevalence of the disease and points at ER homeostasis as a common pathway affected in ADTKD-REN, and possibly more generally in ADTKD.

A review on autosomal dominant tubulointerstitial kidney disease

In recent years there has been a reclassification of hereditary tubulointerstitial renal diseases. The old concepts of nephronoptisis or medullary cystic disease have been reordered based on the discovery of new genes. The 2015 KDIGO guidelines proposed a unification of terminology, diagnostic criteria and monitoring. So far 4genes causing autosomal dominant tubulointerstitial kidney disease have been described: MUC1, UMOD, HNF1B and REN. Although the mutation in each of them causes distinctive features in how they present, all have in common the progressive tubulointerstitial damage and renal fibrosis. In this article, we present a review of the guidelines and the literature, and some practical recommendations for dealing with this disease.

Plasma cell deficiency in human subjects with heterozygous mutations in Sec61 translocon alpha 1 subunit (SEC61A1)

BACKGROUND

Primary antibody deficiencies (PADs) are the most frequent primary immunodeficiencies in human subjects. The genetic causes of PADs are largely unknown. Sec61 translocon alpha 1 subunit (SEC61A1) is the major subunit of the Sec61 complex, which is the main polypeptide-conducting channel in the endoplasmic reticulum membrane. SEC61A1 is a target gene of spliced X-box binding protein 1 and strongly induced during plasma cell (PC) differentiation.

OBJECTIVE

We identified a novel genetic defect and studied its pathologic mechanism in 11 patients from 2 unrelated families with PADs.

METHODS

Whole-exome and targeted sequencing were conducted to identify novel genetic mutations. Functional studies were carried out ex vivo in primary cells of patients and in vitro in different cell lines to assess the effect of SEC61A1 mutations on B-cell differentiation and survival.

RESULTS

We investigated 2 families with patients with hypogammaglobulinemia, severe recurrent respiratory tract infections, and normal peripheral B- and T-cell subpopulations. On in vitro stimulation, B cells showed an intrinsic deficiency to develop into PCs. Genetic analysis and targeted sequencing identified novel heterozygous missense (c.254T>A, p.V85D) and nonsense (c.1325G>T, p.E381*) mutations in SEC61A1, segregating with the disease phenotype. SEC61A1-V85D was deficient in cotranslational protein translocation, and it disturbed the cellular calcium homeostasis in HeLa cells. Moreover, SEC61A1-V85D triggered the terminal unfolded protein response in multiple myeloma cell lines.

CONCLUSION

We describe a monogenic defect leading to a specific PC deficiency in human subjects, expanding our knowledge about the pathogenesis of antibody deficiencies.

Discovery of a novel dominant mutation in the REN gene after forty years of renal disease: a case report

Background

Heterozygous mutations in the gene encoding renin (REN) cause autosomal dominant tubulointerstitial kidney disease (ADTKD), early-onset anaemia and hyperuricaemia; only four different mutations have been described in the published literature to date. We report a novel dominant REN mutation discovered in an individual after forty years of renal disease.

Case presentation

A 57 year old Caucasian woman with chronic kidney disease stage five was reviewed in a regional joint renal genetics clinic. She had initially been diagnosed with chronic pyelonephritis in adolescence, around the same time that she was investigated for anaemia out of keeping with her degree of renal impairment. Hyperuricaemia was identified in her twenties following an episode of gout. A diagnosis of ADTKD was not made until the age of 37 years, when her mother was also found to have kidney disease and commenced haemodialysis. The patient’s renal function continued to slowly deteriorate and, twenty years later, her sister was worked up as a potential donor for kidney transplantation. Revisiting the maternal family history during the transplant work up prompted a referral to clinical genetics and urgent REN genetic testing was requested for the patient, leading to discovery of a heterozygous mutation in the REN gene: c.49 T > C, p.(Trp17Arg). This variant was not identified in her otherwise healthy sister, allowing pre-emptive live renal transplantation to take place shortly afterwards.

Conclusions

In an era where genetic testing is becoming much more readily available, this case highlights the importance of considering a genetic aetiology in all patients with long-standing renal disease and a relevant family history. Establishing a genetic diagnosis of ADTKD-REN in this individual with chronic anaemia, hyperuricaemia and slowly progressive renal impairment helped to identify a suitable live kidney donor and allowed successful pre-emptive transplantation to take place.

Nephron number, hypertension, and CKD: physiological and genetic insight from humans and animal models

The kidneys play a vital role in the excretion of waste products and the regulation of electrolytes, maintenance of acid-base balance, regulation of blood pressure, and production of several hormones. Any alteration in the structure of the nephron (basic functional unit of the kidney) can have a major impact on the kidney's ability to work efficiently. Progressive decline in kidney function can lead to serious illness and ultimately death if not treated by dialysis or transplantation. While there have been numerous studies that implicate lower nephron numbers as being an important factor in influencing susceptibility to developing hypertension and chronic kidney disease, a direct association has been difficult to establish because of three main limitations: 1) the large variation in nephron number observed in the human population; 2) no established reliable noninvasive methods to determine nephron complement; and 3) to date, nephron measurements have been done after death, which doesn't adequately account for potential loss of nephrons with age or disease. In this review, we will provide an overview of kidney structure/function, discuss the current literature for both humans and other species linking nephron deficiency and cardio-renal complications, as well as describe the major molecular signaling factors involved in nephrogenesis that modulate variation in nephron number. As more detailed knowledge about the molecular determinants of nephron development and the role of nephron endowment in the cardio-renal system is obtained, it will hopefully provide clinicians the ability to accurately identify people at risk to develop CKD/hypertension and lead to a shift in patient care from disease treatment to prevention.

Renal tubular dysgenesis: antenatal ultrasound scanning and molecular investigations in a Saudi Arabian family

Autosomal recessive renal tubular dysgenesis (RTD) is a rare lethal disease affecting renal development before birth. RTD is manifested by anuria and severe hypotension resulting in oligohydramnios and birth defects known as Potter's syndrome. Homozygous or compound heterozygous mutations in genes encoding components of the renin-angiotensin system (ACE, AGT, AGTR1 and REN) have been reported to cause RTD. A consanguineous family with a history of multiple stillbirths was investigated using prenatal ultrasound and molecular genetic analysis of an affected foetus. Prenatal ultrasound scan suggested RTD, and a novel homozygous frameshift mutation c.299_300delAA (p.Lys100Serfs*4) in the REN gene was identified by whole-exome sequencing, which segregated with parental DNA samples. RTD remains a rare but important cause of prenatal and perinatal death and may present with antenatally hyperechogenic kidneys.

Autosomal dominant tubulointerstitial kidney disease: diagnosis, classification, and management--A KDIGO consensus report

Rare autosomal dominant tubulointerstitial kidney disease is caused by mutations in the genes encoding uromodulin (UMOD), hepatocyte nuclear factor-1β (HNF1B), renin (REN), and mucin-1 (MUC1). Multiple names have been proposed for these disorders, including 'Medullary Cystic Kidney Disease (MCKD) type 2', 'Familial Juvenile Hyperuricemic Nephropathy (FJHN)', or 'Uromodulin-Associated Kidney Disease (UAKD)' for UMOD-related diseases and 'MCKD type 1' for the disease caused by MUC1 mutations. The multiplicity of these terms, and the fact that cysts are not pathognomonic, creates confusion. Kidney Disease: Improving Global Outcomes (KDIGO) proposes adoption of a new terminology for this group of diseases using the term 'Autosomal Dominant Tubulointerstitial Kidney Disease' (ADTKD) appended by a gene-based subclassification, and suggests diagnostic criteria. Implementation of these recommendations is anticipated to facilitate recognition and characterization of these monogenic diseases. A better understanding of these rare disorders may be relevant for the tubulointerstitial fibrosis component in many forms of chronic kidney disease.

Uromodulin: old friend with new roles in health and disease

The most abundant urinary protein, Tamm-Horsfall protein, later renamed uromodulin, is expressed exclusively by the thick ascending limb cells of the kidney and released into urine from the apical cell membrane. Uromodulin is believed to protect against urinary tract infections and stones, but its other physiologic functions have remained obscure until recently. Renewed interest in uromodulin has been brought about by the identification of uromodulin mutations as causes of a discrete group of diseases that are distinct from nephronophthisis. The three overlapping clinical uromodulin-associated kidney diseases (UAKD) are medullary cystic disease type 2, familial juvenile hyperuricemic nephropathy and glomerulocystic kidney disease. Previously thought of as "adult diseases", it is now recognized that they may also present in childhood and even in infancy. Common characteristics of all three diseases are autosomal dominant inheritance, unremarkable urine sediment and slow progression to end-stage renal disease (ESRD). They are frequently associated with hyperuricemia and gout. These diseases appear to result from failure of the mutant uromodulin to be incorporated into the apical cilium, thereby placing UAKD in the category of "ciliopathies". In addition to causing specific UAKD, certain uromodulin gene polymorphisms have been linked to ESRD in general, suggesting that uromodulin plays a modulatory role in kidney disease progression.

Renal tubular dysgenesis

Renal tubular dysgenesis (RTD) is a severe foetal disorder characterised by the absence or poor development of proximal tubules, early onset and persistent anuria (leading to oligohydramnios and the Potter sequence) and ossification defects of the skull. In most cases, early death occurs from pulmonary hypoplasia, anuria and refractory arterial hypotension. RTD may be acquired during foetal development or inherited as an autosomal recessive disease. Inherited RTD is genetically heterogeneous and linked to mutations in the genes encoding the major components of the renin-angiotensin system (RAS): angiotensinogen, renin, angiotensin-converting enzyme or angiotensin II receptor type 1. Mutations result in either the absence of production or lack of efficacy of angiotensin II. Secondary RTD has been observed in various situations, particularly in the donor twin of severe twin-to-twin transfusion syndrome, in foetuses affected with congenital haemochromatosis or in foetuses exposed to RAS blockers. All cases result in renal hypoperfusion. These examples illustrate the importance of a functional RAS in the maintenance of blood pressure and renal blood flow for humans during foetal life. The diagnosis of RTD in an anuric foetus with normal renal sonography results is important for the management of the foetus or neonate. Depending on the genetic or secondary cause of the disease, such findings can lead to genetic counselling or the prevention of recurrence in subsequent pregnancies.

Analysis of WNT9B mutations in Chinese women with Mayer-Rokitansky-Küster-Hauser syndrome

Mayer–Rokitansky–Küster–Hauser (MRKH) syndrome is a rare congenital female genital anomaly, which is caused by aplasia of the caudalportion of the Müllerian duct. The WNT9B gene encodes a secretory glycoprotein essential for the caudal extension of the Müllerian duct during embryonic development in mice. Coding regions and exon/intron boundaries of the WNT9B gene were amplified and sequenced in 42 Chinese women with MRKH syndrome and 42 controls. Two novel heterozygous mutationswere identified,which were absent in controls. Onewas amissensemutation in exon 1, and the other was located in the 30-untranslated region. Both variants were detected in one out of 42 patients. The two novel mutations may be pathogenic variants in MRKH patients and warrant further functional study.

Novel genetic aspects of congenital anomalies of kidney and urinary tract

PURPOSE OF REVIEW

Congenital anomalies of the kidney and urinary tract (CAKUT) are among the most frequent organ malformations. They are a relevant cause of chronic renal failure in children. Apart from isolated forms of CAKUT, more than 500 syndromes have been described that are characterized by combined defects of the kidney and other organ systems. Familial aggregation of renal malformations in approximately 10% of patients suggests that genetic events might be involved. Modifying effects due to missense mutations in additional developmental genes seem to enhance the phenotypic variability in affected families. In these families, genetic counseling can be difficult. In contrast, in patients with defined autosomal dominant disease, genetic counseling is of high clinical relevance, also with respect to additional extrarenal symptoms.

RECENT FINDINGS

Due to the development of numerous genetic knock-out mouse models, the identification of specific renal developmental genes and the application of novel sequencing techniques of the human genome, our understanding of kidney organogenesis has largely improved during very recent years.

SUMMARY

This review will focus on important genetic factors that influence nephrogenesis and highlight important human disorders that are associated with anomalies of kidneys, proximal and distal urinary tract.