Severe prenatal renal anomalies associated with mutations in HNF1B or PAX2 genes

Immunoexpression Pattern of Autophagy-Related Proteins in Human Congenital Anomalies of the Kidney and Urinary Tract

The purpose of this study was to evaluate the spatiotemporal immunoexpression pattern of microtubule-associated protein 1 light chain 3 beta (LC3B), glucose-regulated protein 78 (GRP78), heat shock protein 70 (HSP70), and lysosomal-associated membrane protein 2A (LAMP2A) in normal human fetal kidney development (CTRL) and kidneys affected with congenital anomalies of the kidney and urinary tract (CAKUT). Human fetal kidneys (control, horseshoe, dysplastic, duplex, and hypoplastic) from the 18th to the 38th developmental week underwent epifluorescence microscopy analysis after being stained with antibodies. Immunoreactivity was quantified in various kidney structures, and expression dynamics were examined using linear and nonlinear regression modeling. The punctate expression of LC3B was observed mainly in tubules and glomerular cells, with dysplastic kidneys displaying distinct staining patterns. In the control group's glomeruli, LAMP2A showed a sporadic, punctate signal; in contrast to other phenotypes, duplex kidneys showed significantly stronger expression in convoluted tubules. GRP78 had a weaker expression in CAKUT kidneys, especially hypoplastic ones, while normal kidneys exhibited punctate staining of convoluted tubules and glomeruli. HSP70 staining varied among phenotypes, with dysplastic and hypoplastic kidneys exhibiting stronger staining compared to controls. Expression dynamics varied among observed autophagy markers and phenotypes, indicating their potential roles in normal and dysfunctional kidney development.

1H, 13C and 15N backbone resonance assignments of hepatocyte nuclear factor-1-beta (HNF1β) POUS and POUHD

Hepatocyte nuclear factor 1β (HNF1β) is a transcription factor that plays a key role in the development and function of the liver, pancreas, and kidney. HNF1β plays a key role in early vertebrate development and the morphogenesis of these organs. In humans, heterozygous mutations in the HNF1B gene can result in organ dysplasia, making it the most common cause of developmental renal diseases, including renal cysts, renal malformations, and familial hypoplastic glomerular cystic kidney disease. Pathogenic variants in the HNF1B gene are known to cause various diseases, including maturity-onset diabetes of the young and developmental renal diseases. This study presents the backbone resonance assignments of HNF1β POUS and POUHD domains, which are highly conserved domains required for the recognition of double-stranded DNA. Our data will be useful for NMR studies to verify the altered structures and functions of mutant HNF1B proteins that can induce developmental renal diseases, including renal cysts, renal malformations, and familial hypoplastic glomerular cystic kidney disease. This study will provide the structural basis for future studies to elucidate the molecular mechanisms underlying how mutations in HNF1β cause diseases.

Maternal periconceptional folic acid supplementation and risk for fetal congenital genitourinary system defects

BACKGROUND

Taking folic acid supplementation could reduce the risk of neural tube defects for offspring in the maternal periconceptional period, but the relationship between folic acid use and other birth defects remains unclear, such as genitourinary system birth defects.

METHODS

The data from a Prenatal Health Care System and Birth Defects Surveillance System in Tongzhou, Beijing, China, were collected from 2013 to 2018. We adjusted for differences in characteristics between comparison groups using propensity score inverse probability weighting and assessed associations with Poisson regression modeling.

RESULTS

A total of 65,418 live births and stillbirths were included, and there were 194 cases with congenital genitourinary defects among them. The prevalence of genitourinary system birth defects was 29.2 (34.9) per 10,000 for FA/MMFA users (nonusers). Compared to nonusers, FA/MMFA users had a lower risk for genitourinary system birth defects (adjusted risk ratio [aRR] 0.81, 95% confidence interval [CI] 0.67, 0.98), and for hypospadias (aRR 0.55, 95% CI 0.40, 0.76).

CONCLUSIONS

FA or MMFA supplementation during the maternal periconceptional period could reduce the risk for genitourinary system birth defects in offspring. More mechanisms should be explored for the protective effect.

IMPACT

Folic acid (FA) or multiple micronutrients containing folic acid (MMFA) supplementation during the maternal periconceptional period could reduce the risk for genitourinary system birth defects in offspring. Maternal FA/MMFA supplementation during the periconceptional period may reduce the risk for hypospadias.

The genetic etiologies of bilateral renal agenesis

OBJECTIVE

The goal of this study was to review and analyze the medical literature for cases of prenatal and/or postnatally diagnosed bilateral renal agenesis (BRA) and create a comprehensive summary of the genetic etiologies known to be associated with this condition.

METHODS

A literature search was conducted as a scoping review employing Online Mendeliain Inheritance in Man, PubMed, and Cochrane to identify cases of BRA with known underlying genetic (chromosomal vs. single gene) etiologies and those described in syndromes without any known genetic etiology. The cases were further categorized as isolated versus non-isolated, describing additional findings reported prenatally, postnatally, and postmortem. Inheritance pattern was also documented when appropriate in addition to the reported timing of diagnosis and sex.

RESULTS

We identified six cytogenetic abnormalities and 21 genes responsible for 20 single gene disorders associated with BRA. Five genes have been reported to associate with BRA without other renal anomalies; sixteen others associate with both BRA as well as unilateral renal agenesis. Six clinically recognized syndromes/associations were identified with an unknown underlying genetic etiology. Genetic etiologies of BRA are often phenotypically expressed as other urogenital anomalies as well as complex multi-system syndromes.

CONCLUSION

Multiple genetic etiologies of BRA have been described, including cytogenetic abnormalities and monogenic syndromes. The current era of the utilization of exome and genome-wide sequencing is likely to significantly expand our understanding of the underlying genetic architecture of BRA.

Phenotype-Genotype Correlations in Three Different Cases of Adult-Onset Genetic Focal Segmental Glomerulosclerosis

This study highlights the importance of a combined diagnostic approach in the diagnosis of rare diseases, such as adult-onset genetic FSGS. We present three adult patient cases evaluated with kidney biopsy for proteinuria, chronic kidney disease, and hypertension, which were suggestive of adult-onset genetic FSGS. Renal biopsy samples and formalin-fixed, paraffin-embedded fetal kidneys were evaluated using standard light microscopical stainings, direct immunofluorescence on cryostat sections, and electron microscopy. Clinical exome sequencing was performed for each case, and 45 FSGS-related genes were analyzed. Identifying mutations in the PAX2, ACTN4, and COL4A5 genes have prompted a re-evaluation of the previous histopathological examinations. The PAX2 mutation led to a thinner nephrogenic zone and decreased number of glomeruli, resulting in oligohydramnios during fetal development and oligomeganephronia and adaptive focal-segmental glomerulosclerosis in adulthood. The ACTN4 mutation caused distinct electron-dense aggregates in podocyte cell bodies, while the COL4A5 mutation led to segmental sclerosis of glomeruli with marked interstitial fibrosis and tubular atrophy. The identification of specific mutations and their histopathological consequences can lead to a better understanding of the disease and its progression, as well as potential treatment options.

Overexpression of long noncoding RNA 4933425B07Rik leads to renal hypoplasia by inactivating Wnt/β-catenin signaling pathway

Congenital anomalies of the kidney and urinary tract (CAKUT) is a general term for a class of diseases that are mostly caused by intrauterine genetic development limitation. Without timely intervention, certain children with CAKUT may experience progressive decompensation and a rapid decline in renal function, which will ultimately result in end-stage renal disease. At present, a comprehensive understanding of the pathogenic signaling events of CAKUT is lacking. The role of long noncoding RNAs (lncRNAs) in renal development and disease have recently received much interest. In previous research, we discovered that mice overexpressing the lncRNA 4933425B07Rik (Rik) showed a range of CAKUT phenotypes, primarily renal hypoplasia. The current study investigated the molecular basis of renal hypoplasia caused by Rik overexpression. We first used Rapid Amplification of cDNA ends (RACE) to obtain the full-length sequence of Rik in Rik +/+;Hoxb7 mice. Mouse proximal renal tubule epithelial cells (MPTCs) line with Rik overexpression was constructed using lentiviral methods, and mouse metanephric mesenchyme cell line (MK3) with Rik knockout was then constructed by the CRISPR‒Cas9 method. We performed RNA-seq on the Rik-overexpressing cell line to explore possible differentially expressed molecules and pathways. mRNA expression was confirmed by qRT‒PCR. Reduced levels of Wnt10b, Fzd8, and β-catenin were observed when Rik was expressed robustly. On the other hand, these genes were more highly expressed when Rik was knocked out. These results imply that overabundance of Rik might inhibit the Wnt/β-catenin signaling pathway, which may result in renal hypoplasia. In general, such research might help shed light on CAKUT causes and processes and offer guidance for creating new prophylactic and therapeutic strategies.

The role of genetic testing in the diagnostic workflow of pediatric patients with kidney diseases: the experience of a single institution

PURPOSE

Inherited kidney diseases are among the leading causes of kidney failure in children, resulting in increased mortality, high healthcare costs and need for organ transplantation. Next-generation sequencing technologies can help in the diagnosis of rare monogenic conditions, allowing for optimized medical management and therapeutic choices.

METHODS

Clinical exome sequencing (CES) was performed on a cohort of 191 pediatric patients from a single institution, followed by Sanger sequencing to confirm identified variants and for family segregation studies.

RESULTS

All patients had a clinical diagnosis of kidney disease: the main disease categories were glomerular diseases (32.5%), ciliopathies (20.4%), CAKUT (17.8%), nephrolithiasis (11.5%) and tubular disease (10.5%). 7.3% of patients presented with other conditions. A conclusive genetic test, based on CES and Sanger validation, was obtained in 37.1% of patients. The highest detection rate was obtained for ciliopathies (74.4%), followed by nephrolithiasis (45.5%), tubular diseases (45%), while most glomerular diseases and CAKUT remained undiagnosed.

CONCLUSIONS

Results indicate that genetic testing consistently used in the diagnostic workflow of children with chronic kidney disease can (i) confirm clinical diagnosis, (ii) provide early diagnosis in the case of inherited conditions, (iii) find the genetic cause of previously unrecognized diseases and (iv) tailor transplantation programs.

Prenatal Diagnosis of Intragenic HNF1B Variant-Associated Renal Disease by Exome Sequencing

Introduction

HNF1B-associated diseases are a group of genetic conditions that affect the kidney as well as other organ systems. Kidney anomalies are the most common symptoms. Other defects may include early-onset diabetes, genital abnormalities, and abnormalities of pancreas and liver function. Renal involvement has emerged as the earliest finding in HNF1B disease, even in prenatal life, with the most common feature being hyperechogenic kidneys.

Case Presentation

In this study, we present 3 fetuses with bilateral renal hyperechogenicity identified by ultrasound in the second trimester. No pathogenic copy number variations were revealed by amniocentesis with chromosomal microarray analysis (CMA). Heterozygous variants in HNF1B were detected in all 3 fetuses by further investigation with exome sequencing (ES). Two pregnancies were terminated, and one was continued to term.

Discussion and Conclusion

Because of the known high frequency of HNF1B aberrations in fetal hyperechogenic kidneys, HNF1B screening should be an integral part of prenatal diagnosis for such fetuses. ES should be recommended following or concurrently with CMA for rapid prenatal detection. The ES results would improve the diagnostic yield and are beneficial in guiding counseling and management.

Transcription factor HNF1β controls a transcriptional network regulating kidney cell structure and tight junction integrity

Mutations in the hepatocyte nuclear factor (HNF)1β gene (HNF1B) cause autosomal dominant tubulointerstitial kidney disease, a rare and heterogeneous disease characterized by renal cysts and/or malformation, maturity-onset diabetes of the young, hypomagnesemia, and hypokalemia. The electrolyte disturbances may develop in the distal part of the nephron, which is important for fine-tuning of Mg²⁺ and Ca²⁺ reabsorption. Therefore, we aimed to study the transcriptional network directed by HNF1β in the distal part of the nephron. We combined HNF1β chromatin immunoprecipitation-sequencing and mRNA expression data to identify direct targets of HNF1β in a renal distal convoluted tubule cell line (mpkDCT). Gene Ontology term pathway analysis demonstrated enrichment of cell polarity, cell-cell junction, and cytoskeleton pathways in the dataset. Genes directly and indirectly regulated by HNF1β within these pathways included members of the apical and basolateral polarity complexes including Crumbs protein homolog 3 (Crb3), partitioning defective 6 homolog-β (Pard6b), and LLGL Scribble cell polarity complex component 2 (Llgl2). In monolayers of mouse inner medullary collecting duct 3 cells expressing dominant negative Hnf1b, tight junction integrity was compromised, as observed by reduced transepithelial electrical resistance values and increased permeability for fluorescein (0.4 kDa) compared with wild-type cells. Expression of dominant negative Hnf1b also led to a decrease in height (30%) and an increase in surface (58.5%) of cells grown on membranes. Moreover, three-dimensional spheroids formed by cells expressing dominant negative Hnf1b were reduced in size compared with wild-type spheroids (30%). Together, these findings demonstrate that HNF1β directs a transcriptional network regulating tight junction integrity and cell structure in the distal part of the nephron.NEW & NOTEWORTHY Genetic defects in transcription factor hepatocyte nuclear factor (HNF)1β cause a heterogeneous disease characterized by electrolyte disturbances, kidney cysts, and diabetes. By combining RNA-sequencing and HNF1β chromatin immunoprecipitation-sequencing data, we identified new HNF1β targets that were enriched for cell polarity pathways. Newly discovered targets included members of polarity complexes Crb3, Pard6b, and Llgl2. Functional assays in kidney epithelial cells demonstrated decreased tight junction integrity and a loss of typical cuboidal morphology in mutant Hnf1b cells.

Potter Deformation Sequence Caused by 17q12 Deletion: A Lethal Constellation

17q12 deletion syndrome causes developmental abnormalities of the kidneys, pancreas, genital tract, and neurodevelopment, and it has a wide range of phenotypes ranging from fetal demise to normal adulthood with minimal renal impairment. Here we describe a rare case of 17q12 deletion diagnosed prenatally, complicated by anhydramnios and Potter sequence. The baby was born but necessitated life-saving interventions due to pulmonary and renal insufficiency and ultimately succumbed to multi-organ failure. We present full autopsy results describing findings linked to 17q12 deletion, including severe bilateral multicystic renal dysplasia, pancreatic hypoplasia, and cysts adjacent to the Fallopian tubes. We also describe pulmonary hypoplasia and Potter facies as consequences of anhydramnios. We correlate these findings to our current understanding of molecular signals altered by 17q12 deletion, notably affecting HNF1B and LHX1 genes, which are known to mediate renal and genitourinary tract development.

Aberrations in FGFR1, FGFR2, and RIP5 Expression in Human Congenital Anomalies of the Kidney and Urinary Tract (CAKUT)

This study aimed to explore the spatio-temporal expression patterns of congenital anomalies of kidney and urinary tract (CAKUT) candidate genes, Fibroblast Growth Factor Receptor 1 (FGFR1), Fibroblast Growth Factor Receptor 2 (FGFR2) and Receptor-Interacting Protein Kinase 5 (RIP5), in human fetal kidney development (CTRL) and kidneys affected with CAKUT. Human fetal kidneys from the 22nd to 41st developmental week (duplex, hypoplastic, dysplastic, and controls) were stained with antibodies and analyzed by epifluorescence microscopy and RT-qPCR. The effect of CAKUT candidate genes on kidney nephrogenesis and function is confirmed by statistically significant variations in the spatio-temporal expression patterns of the investigated markers. The nuclear localization of FGFR1, elevated expression score of FGFR1 mRNA, the increased area percentage of FGFR1-positive cells in the kidney cortex, and the overall decrease in the expression after the peak at the 27th developmental week in dysplastic kidneys (DYS), suggest an altered expression pattern and protein function in response to CAKUT pathophysiology. The RT-qPCR analysis revealed a significantly higher FGFR2 mRNA expression score in the CAKUT kidneys compared to the CTRL. This increase could be due to the repair mechanism involving the downstream mediator, Extracellular Signal-Regulated Kinase 1/2 (ERK1/2). The expression of RIP5 during normal human kidney development was reduced temporarily, due to urine production and increased later since it undertakes additional functions in the maturation of the postnatal kidney and homeostasis, while the expression dynamics in CAKUT-affected kidneys exhibited a decrease in the percentage of RIP5-positive cells during the investigated developmental period. Our findings highlight the importance of FGFR1, FGFR2, and RIP5 as markers in normal and pathological kidney development.

The genetic basis of congenital anomalies of the kidney and urinary tract

During the past decades, remarkable progress has been made in our understanding of the molecular basis of kidney diseases, as well as in the ability to pinpoint disease-causing genetic changes. Congenital anomalies of the kidney and urinary tract (CAKUT) are remarkably diverse, and may be either isolated to the kidney or involve other systems, and are notorious in their variable genotype-phenotype correlations. Genetic conditions underlying CAKUT are individually rare, but collectively contribute to disease etiology in ~ 16% of children with CAKUT. In this review, we will discuss basic concepts of kidney development and genetics, common causes of monogenic CAKUT, and the approach to diagnosing and managing a patient with suspected monogenic CAKUT. Altogether, the concepts presented herein represent an introduction to the emergence of nephrogenetics, a fast-growing multi-disciplinary field that is focused on deciphering the causes and manifestations of genetic kidney diseases as well as providing the framework for managing patients with genetic forms of CAKUT.

The causes and consequences of paediatric kidney disease on adult nephrology care

Adult nephrologists often look after patients who have been diagnosed with kidney disease in childhood. This does present unique challenges to the adult nephrologist, who may be unfamiliar with the underlying cause of kidney disease as well as the complications of chronic kidney disease (CKD) that may have accumulated during childhood. This review discusses common causes of childhood CKD, in particular congenital anomalies of the kidney and urinary tract (CAKUT), autosomal dominant tubulointerstitial kidney disease (ADTKD), polycystic kidney disease, hereditary stone disease, nephrotic syndrome and atypical haemolytic uraemic syndrome. The long-term consequences of childhood CKD, such as the cardiovascular consequences, cognition and education as well as bone health, nutrition and growth are also discussed.

Mechanisms of ion transport regulation by HNF1β in the kidney: beyond transcriptional regulation of channels and transporters

Hepatocyte nuclear factor 1β (HNF1β) is a transcription factor essential for the development and function of the kidney. Mutations in and deletions of HNF1β cause autosomal dominant tubule interstitial kidney disease (ADTKD) subtype HNF1β, which is characterized by renal cysts, diabetes, genital tract malformations, and neurodevelopmental disorders. Electrolyte disturbances including hypomagnesemia, hyperuricemia, and hypocalciuria are common in patients with ADTKD-HNF1β. Traditionally, these electrolyte disturbances have been attributed to HNF1β-mediated transcriptional regulation of gene networks involved in ion transport in the distal part of the nephron including FXYD2, CASR, KCNJ16, and FXR. In this review, we propose additional mechanisms that may contribute to the electrolyte disturbances observed in ADTKD-HNF1β patients. Firstly, kidney development is severely affected in Hnf1b-deficient mice. HNF1β is required for nephron segmentation, and the absence of the transcription factor results in rudimentary nephrons lacking mature proximal tubule, loop of Henle, and distal convoluted tubule cluster. In addition, HNF1β is proposed to be important for apical-basolateral polarity and tight junction integrity in the kidney. Interestingly, cilia formation is unaffected by Hnf1b defects in several models, despite the HNF1β-mediated transcriptional regulation of many ciliary genes. To what extent impaired nephron segmentation, apical-basolateral polarity, and cilia function contribute to electrolyte disturbances in HNF1β patients remains elusive. Systematic phenotyping of Hnf1b mouse models and the development of patient-specific kidney organoid models will be essential to advance future HNF1β research.

Multidisciplinary approaches for elucidating genetics and molecular pathogenesis of urinary tract malformations

Advances in clinical diagnostics and molecular tools have improved our understanding of the genetically heterogeneous causes underlying congenital anomalies of kidney and urinary tract (CAKUT). However, despite a sharp incline of CAKUT reports in the literature within the past 2 decades, there remains a plateau in the genetic diagnostic yield that is disproportionate to the accelerated ability to generate robust genome-wide data. Explanations for this observation include (i) diverse inheritance patterns with incomplete penetrance and variable expressivity, (ii) rarity of single-gene drivers such that large sample sizes are required to meet the burden of proof, and (iii) multigene interactions that might produce either intra- (e.g., copy number variants) or inter- (e.g., effects in trans) locus effects. These challenges present an opportunity for the community to implement innovative genetic and molecular avenues to explain the missing heritability and to better elucidate the mechanisms that underscore CAKUT. Here, we review recent multidisciplinary approaches at the intersection of genetics, genomics, in vivo modeling, and in vitro systems toward refining a blueprint for overcoming the diagnostic hurdles that are pervasive in urinary tract malformation cohorts. These approaches will not only benefit clinical management by reducing age at molecular diagnosis and prompting early evaluation for comorbid features but will also serve as a springboard for therapeutic development.

Targeted next-generation sequencing in a large series of fetuses with severe renal diseases

We report the screening of a large panel of genes in a series of 100 fetuses (98 families) affected with severe renal defects. Causative variants were identified in 22% of cases, greatly improving genetic counseling. The percentage of variants explaining the phenotype was different according to the type of phenotype. The highest diagnostic yield was found in cases affected with the ciliopathy-like phenotype (11/15 families and, in addition, a single heterozygous or a homozygous Class 3 variant in PKHD1 in three unrelated cases with autosomal recessive polycystic kidney disease). The lowest diagnostic yield was observed in cases with congenital anomalies of the kidney and urinary tract (9/78 families and, in addition, Class 3 variants in GREB1L in three unrelated cases with bilateral renal agenesis). Inheritance was autosomal recessive in nine genes (PKHD1, NPHP3, CEP290, TMEM67, DNAJB11, FRAS1, ACE, AGT, and AGTR1), and autosomal dominant in six genes (PKD1, PKD2, PAX2, EYA1, BICC1, and MYOCD). Finally, we developed an original approach of next-generation sequencing targeted RNA sequencing using the custom capture panel used for the sequencing of DNA, to validate one MYOCD heterozygous splicing variant identified in two male siblings with megabladder and inherited from their healthy mother.

Deciphering the mutation spectrum in south Indian children with congenital anomalies of the kidney and urinary tract

BACKGROUND

Congenital anomalies of the kidney and urinary tract (CAKUT) cover a spectrum of structural malformations that result from aberrant morphogenesis of kidney and urinary tract. It is the most prevalent cause of kidney failure in children. Hence, it is important from a clinical perspective to unravel the molecular etiology of kidney and urinary tract malformations. Causal variants in genes that direct various stages of development of kidney and urinary tract in fetal life have been identified in 5-20% of CAKUT patients from Western countries. Recent advances in next generation sequencing technology and decreasing cost offer the opportunity to characterize the genetic profile of CAKUT in Indian population and facilitate integration of genetic diagnostics in care of children with CAKUT.

METHODS

Customized targeted panel sequencing was performed to identify pathogenic variants in 31 genes known to cause human CAKUT in 69 south Indian children with CAKUT. The NGS data was filtered using standardized pipeline and the variants were classified using ACMG criteria. Genotype and phenotype correlations were performed.

RESULTS

The cohort consisted of children mostly with posterior urethral valve (PUV) (39.1%), vesico-ureteric reflux (VUR) (33.3%) and multi-cystic dysplastic kidney (MCDK) (7.2%). No pathogenic or likely pathogenic variants were identified in the study. Most of our variants (n = 39, 60%) were variants of unknown significance with 25.6% (10/39) of them were identified as potentially damaging but were novel variants.

CONCLUSIONS

The present study did not identify any disease-causing monogenic variants in the cohort. The absence of genetic cause may be due to limitations of panel-based testing and also due to higher proportion of children with abnormalities in lower urinary tract than hypodysplasia of kidneys. Clinical, larger targeted panel or whole exome sequencing may be a better method to characterize the genetic profile of Indians patients with CAKUT.

The term CAKUT has outlived its usefulness: the case for the defense

Congenital anomalies of the kidney and urinary tract form a spectrum of congenital structural disorders that are generally known under the term CAKUT. The term CAKUT was introduced 20 years ago and has been used extensively in literature since. Prof. Woolf has made a plea for abandoning this term in his "case for the prosecution." Here, I advocate for the continued use of CAKUT as an umbrella term for these related congenital kidney and urinary tract abnormalities. I explain why the term CAKUT accurately and usefully defines this group of related structural disorders with prenatal origin and why it makes sense to continue grouping these disorders given accumulating evidence for shared etiology of CAKUT phenotypes and the importance of grouping CAKUT phenotypes in genetic counseling.

Ocular phenotype in a patient with PAX2 gene mutation-associated papillorenal syndrome

BACKGROUND

Papillorenal syndrome is an autosomal dominant disorder associated with mutations in the gene PAX2 and often presents with characteristic and specific optic disc findings, frequently with renal dysplasia. In at least half of cases, an identifiable mutation in the PAX2 gene can be detected. We report the ocular findings in a second case of papillorenal syndrome with the c.350 G > C (p.Arg117Pro) mutation detected within the PAX2 gene.

METHODS

A case report of papillorenal syndrome due to PAX2 mutation. Complete ophthalmologic examination was performed as well as color fundus photography, fundus autofluorescence, and optical coherence tomography (OCT). Genetic testing was performed using a next-generation sequencing with CNV calling (NGS-CNV) panel test containing 55 genes associated with nephrotic syndrome or focal segmental glomerulosclerosis.

RESULTS

An 11-year-old boy who presented with hypertension and proteinuria was found to have stage IV chronic kidney disease. Presenting visual acuity was 20/25 in the right eye and 20/20 in the left eye. The fundus exam showed bilateral centrally excavated optic discs with absent central retinal vessels and a compensatory multiplicity of cilioretinal vessels, characteristic and specific for papillorenal syndrome. OCT showed outer retinal atrophy and macular schisis. Genetic testing identified the likely pathogenic c.350 G > C (p.Arg117Pro) mutation in PAX2.

CONCLUSIONS

We report the first description, to our knowledge, of the clinical presentation, ocular and systemic findings, and ophthalmic imaging in an individual with papillorenal syndrome associated with the PAX2 c.350 G > C (p.Arg117Pro) mutation. Our case adds to the current understanding of papillorenal syndrome and demonstrates that this condition is associated with a pathognomonic optic disc appearance and significant renal disease.

Improving renal phenotype and evolving extra-renal features of 17q12 deletion encompassing the HNF1B gene

BACKGROUND

HNF1B deletion/intragenic mutations are the most commonly identified genetic cause of congenital anomalies of the kidney and urinary tract (CAKUT) suggested by fetal ultrasound findings such as: parenchymal hyperechogenicity, overt cystic changes or gross morphological urinary system (UT) abnormalities. The postnatal evolution of these 17q12 deletions encompassing the HNF1B gene-associated findings has not been assessed in depth.

METHODS

In this observational study, we present postnatal follow-up findings in 5 of 6 cases (one pregnancy was terminated on parental request) of fetal-onset cystic/hyperechogenic kidneys eventually diagnosed with 17q12 microdeletion encompassing the HNF1B gene between 2009 and 2017.

RESULTS

Complete normalization of kidney parenchymal abnormalities and of depressed neonatal renal function was observed in 4/5 and 5/5 patients within 2-4.9 years and 1.5-8 months, respectively. All 5 patients had preserved normal renal function at 3-11 years of follow-up. The evolving later-onset renal features included: hypomagnesemia, hyperuricemia, urinary tract infection (UTI), and bilateral grade 3-4 vesicoureteral reflux and bladder diverticula in 3, 3, 2, and 1 patient, respectively. HNF1B gene deletion-associated extra-renal manifestations with delayed presentation were global developmental delay/autistic spectrum disorder (ASD), rolandic-type seizures, overweight, and borderline fasting hyperglycemia observed in 1-2 patients each. Family history was positive for small-size or asymptomatic cystic kidneys with normal function, diabetes mellitus, seizures, and mental/psychiatric problems in 3/6 cases.

CONCLUSIONS

Fetal-onset HNF1B deletion-associated kidneys' parenchymal abnormalities confirmed postnatally with initially depressed renal function might undergo complete resolution within several years and few months, respectively. However, later-onset urinary tract, metabolic, and neurodevelopmental features of this mutation might appear over years. Therefore, genetic molecular evaluation/diagnosis and continuous follow-up for evolving features are mandatory in affected children.

Intrauterine Low-Protein Diet Exacerbates Abnormal Development of the Urinary System in Gen1-Mutant Mice

BACKGROUND

Gen1 mutation can cause various phenotypes of congenital anomaly of the kidney and urinary tract (CAKUT). An intrauterine low-protein isocaloric diet can also cause CAKUT phenotypes in offspring. However, single factors such as gene mutation or abnormal environmental factor during pregnancy can only explain part of the pathogenesis of CAKUT.

OBJECTIVES

A low-protein isocaloric diet was fed to Gen1-mutant mice throughout pregnancy to establish a Gen1-mutant mouse model exposed to a low-protein isocaloric intrauterine environment. The mice were divided into 4 groups: normal (22%) protein diet (ND) + wild-type mice (CON group), ND + Gen1^PB/+ mice (Gen1^PB/+ group), low (6%)-protein isocaloric diet (LD) + wild-type mice (LD group), and the LD + Gen1^PB/+ groups.

METHODS

The experimental design included observing proportion and distribution of CAKUT phenotypes of neonatal mice; evaluating the number of ureteric buds (UBs) on embryonic day (E) 11.5, the location of UBs on E11.5, and length of the common nephric duct (CND); isolating embryonic kidneys on E11.5 from the Gen1^PB/+ group and culturing embryonic kidneys in medium containing 10% serum or serum-free medium to observe the branching of UBs; and detecting the p-PLCγ, p-Akt, and p-ERK1/2 in UBs and CND on E11.5, as well as the apoptosis and proliferation of tissues by immunofluorescence staining.

RESULTS

We found that the incidence of CAKUT in offspring of Gen1^PB/+ mice under an intrauterine low-protein isocaloric diet environment was significantly increased, and a duplicated collecting system was the dominant phenotype of CAKUT. During the early stage of metanephric development, ectopic protrusion of UBs may appear and lower locations of UBs in Gen1^PB/+ mice under an intrauterine low-protein isocaloric diet environment and the number of UB branches in the serum-free culture condition significantly decreased. Further examination revealed that p-PLCγ signaling and tissue apoptosis were abnormal in UBs and the CND at the early stage of kidney development.

CONCLUSIONS

The aforementioned findings suggest that an intrauterine low-protein isocaloric diet can aggravate the occurrence of CAKUT in Gen1-mutant mice, which might affect key steps in the metanephric development, such as the protrusion of UBs, which might be related to mediate UBs and CND apoptosis through p-PLCγ signaling.

A case report with functional characterization of a HNF1B mutation (p.Leu168Pro) causing MODY5

We previously performed next-generation sequencing-based genetic screening in patients with autoantibody-negative type 1 diabetes, and identified the p.Leu168Pro mutation in HNF1B. Here,we report the clinical course of the patient and the results of functional characterization of this mutation. The proband had bilateral renal hypodysplasia and developed insulin-dependent diabetes during childhood. The pathogenicity of Leu168Pro-HNF1B was evaluated with three-dimensional structure modeling, Western blotting, immunofluorescence analysis and luciferase reporter assays using human embryonic kidney 293 cells. Three-dimensional structure modeling predicted that the Leu168 residue is buried in the DNA-binding Pit-Oct-Unc-specific (POU_S) domain and forms a hydrophobic core. Western blotting showed that the protein expression level of Leu168Pro-HNF1B was lower than that of wild-type (WT) HNF1B. Immunofluorescence staining showed that both WT- and Leu168Pro-HNF1B were normally localized in the nucleus. The cells transfected with WT-HNF1B exhibited 5-fold higher luciferase reporter activity than cells transfected with an empty vector. The luciferase activities were comparable between WT-HNF1B/Leu168Pro-HNF1B and WT-HNF1B/empty vector co-transfection. In conclusion, Leu168Pro is a protein-destabilizing HNF1B mutation, and the destabilization is likely due to the structural changes involving the hydrophobic core of POU_S. The disease-causing Leu168Pro HNF1B mutation is a loss-of-function mutation without a dominant-negative effect.

Genetic testing in the diagnosis of chronic kidney disease: recommendations for clinical practice

The overall diagnostic yield of massively parallel sequencing–based tests in patients with chronic kidney disease (CKD) is 30% for paediatric cases and 6–30% for adult cases. These figures should encourage nephrologists to frequently use genetic testing as a diagnostic means for their patients. However, in reality, several barriers appear to hinder the implementation of massively parallel sequencing–based diagnostics in routine clinical practice. In this article we aim to support the nephrologist to overcome these barriers. After a detailed discussion of the general items that are important to genetic testing in nephrology, namely genetic testing modalities and their indications, clinical information needed for high-quality interpretation of genetic tests, the clinical benefit of genetic testing and genetic counselling, we describe each of these items more specifically for the different groups of genetic kidney diseases and for CKD of unknown origin.

Clinical Integration of Genome Diagnostics for Congenital Anomalies of the Kidney and Urinary Tract

Revolutions in genetics, epigenetics, and bioinformatics are currently changing the outline of diagnostics and clinical medicine. From a nephrologist's perspective, individuals with congenital anomalies of the kidney and urinary tract (CAKUT) are an important patient category: not only is CAKUT the predominant cause of kidney failure in children and young adults, but the strong phenotypic and genotypic heterogeneity of kidney and urinary tract malformations has hampered standardization of clinical decision making until now. However, patients with CAKUT may benefit from precision medicine, including an integrated diagnostics trajectory, genetic counseling, and personalized management to improve clinical outcomes of developmental kidney and urinary tract defects. In this review, we discuss the present understanding of the molecular etiology of CAKUT and the currently available genome diagnostic modalities in the clinical care of patients with CAKUT. Finally, we discuss how clinical integration of findings from large-scale genetic, epigenetic, and gene-environment interaction studies may improve the prognosis of all individuals with CAKUT.

Screening of renal anomalies in first-degree relatives of children diagnosed with non-syndromic congenital anomalies of kidney and urinary tract

BACKGROUND

Non-syndromic congenital anomalies of kidney and urinary tract (CAKUT) are usually sporadic in nature but familial clustering of cases have been observed suggesting a genetic predisposition to this condition. We aimed to determine the frequency and pattern of renal anomalies in first-degree relatives of children with non-syndromic CAKUT.

METHODS

We screened all the first-degree relatives of children with CAKUT. A total of 149 first-degree relatives, belonging to 62 families were screened with ultrasonography.

RESULTS

A renal anomaly was detected in 9 out of the 62 families. Two of these nine families had identical anomalies (child and a parent) indicating single-gene disorders with possible autosomal dominant inheritance, while the rest of families had a non-identical anomaly. The anomalies detected in the first-degree relatives were renal hypodysplasia (n = 2), multicystic dysplastic kidney (n = 3), pelviureteric junction obstruction (n = 2) and mild hydronephrosis (n = 2). The incidence of a sonographically detected anatomic renal anomaly in first-degree relatives of children with CAKUT was found to be 6.0%. Familial cystic kidney disease was found in two out of the 4 families with cystic kidney disease.

CONCLUSION

Significant renal anomalies were identified in first-degree relatives of children with non-syndromic CAKUT and hence, attempts must be made to screen the family members of children with non-syndromic CAKUT.

Whole genome sequence analysis identifies a PAX2 mutation to establish a correct diagnosis for a syndromic form of hyperuricemia

Hereditary hyperuricemia may occur as part of a syndromic disorder or as an isolated nonsyndromic disease, and over 20 causative genes have been identified. Here, we report the use of whole genome sequencing (WGS) to establish a diagnosis in a family in which individuals were affected with gout, hyperuricemia associated with reduced fractional excretion of uric acid, chronic kidney disease (CKD), and secondary hyperparathyroidism, that are consistent with familial juvenile hyperuricemic nephropathy (FJHN). However, single gene testing had not detected mutations in the uromodulin (UMOD) or renin (REN) genes, which cause approximately 30-90% of FJHN. WGS was therefore undertaken, and this identified a heterozygous c.226G>C (p.Gly76Arg) missense variant in the paired box gene 2 (PAX2) gene, which co-segregated with renal tubulopathy in the family. PAX2 mutations are associated with renal coloboma syndrome (RCS), which is characterized by abnormalities in renal structure and function, and anomalies of the optic nerve. Ophthalmological examination in two adult brothers affected with hyperuricemia, gout, and CKD revealed the presence of optic disc pits, consistent with optic nerve coloboma, thereby revising the diagnosis from FJHN to RCS. Thus, our results demonstrate the utility of WGS analysis in establishing the correct diagnosis in disorders with multiple etiologies.

[Kidney Cysts and Cystic Nephropathies in Children - A Consensus Guideline by 10 German Medical Societies]

This consensus-based guideline was developed by all relevant German pediatric medical societies. Ultrasound is the standard imaging modality for pre- and postnatal kidney cysts and should also exclude extrarenal manifestations in the abdomen and internal genital organs. MRI has selected indications. Suspicion of a cystic kidney disease should prompt consultation of a pediatric nephrologist. Prenatal management must be tailored to very different degrees of disease severity. After renal oligohydramnios, we recommend delivery in a perinatal center. Neonates should not be denied renal replacement therapy solely because of their age. Children with unilateral multicystic dysplastic kidney do not require routine further imaging or nephrectomy, but long-term nephrology follow-up (as do children with uni- or bilateral kidney hypo-/dysplasia with cysts). ARPKD (autosomal recessive polycystic kidney disease), nephronophthisis, Bardet-Biedl syndrome and HNF1B mutations cause relevant extrarenal disease and genetic testing is advisable. Children with tuberous sclerosis complex, tumor predisposition (e. g. von Hippel Lindau syndrome) or high risk of acquired kidney cysts should have regular ultrasounds. Even asymptomatic children of parents with ADPKD (autosomal dominant PKD) should be monitored for hypertension and proteinuria. Presymptomatic diagnostic ultrasound or genetic examination for ADPKD in minors should only be done after thorough counselling. Simple cysts are very rare in children and ADPKD in a parent should be excluded. Complex renal cysts require further investigation.

PAX2 variant associated with bilateral kidney agenesis and broad intrafamilial disease variability

Pathogenic variants in PAX2 have previously been associated with renal coloboma syndrome. Here we present a novel variant c.68T>C associated with bilateral kidney agenesis, minimal change nephropathy, ureteropelvic junction obstruction, duplex kidney with hydronephrosis of upper pole system and bilateral kidney hypoplasia within the same family. Additionally, two family members were found to have optic nerve abnormalities further supporting the impact of the PAX2 variant. This is the first report of a PAX2 variant associated with bilateral kidney agenesis.

A Primer on Congenital Anomalies of the Kidneys and Urinary Tracts (CAKUT)

Congenital anomalies of the kidneys and urinary tracts (CAKUT) are disorders caused by defects in the development of the kidneys and their outflow tracts. The formation of the kidneys begins at week 3 and nephrogenesis continues until week 36, therefore, the kidneys and outflow tracts are susceptible to environmental risk factors that perturb development throughout gestation. Many genes have been implicated in kidney and outflow tract development, and mutations have been identified in patients with CAKUT. In severe cases of CAKUT, when the kidneys do not form, the fetus will not survive. However, in less severe cases, the baby can survive with combined kidney and outflow tract defects or they may only be identified in adulthood. In this review, we will cover the clinical presentation of CAKUT, its epidemiology, and its long-term outcomes. We will then discuss risk factors for CAKUT, including genetic and environmental contributions. Although severe CAKUT is rare, low nephron number is a much more common disorder with its effect on kidney function increasingly apparent as a person ages. Low nephron number appears to arise by the same mechanisms as CAKUT, but it differs in terms of the magnitude of the insult and the timing of when it occurs during gestation. By understanding the causes of CAKUT and low nephron number, we can begin to identify preventive treatments and establish clinical guidelines for how these patients should be followed.

Etiology and management of early pregnancy renal anhydramnios: Is there a place for serial amnioinfusions?

Early pregnancy renal anhydramios (EPRA) comprises congenital renal disease that results in fetal anhydramnios by 22 weeks of gestation. It occurs in over 1 in 2000 pregnancies and affects 1500 families in the US annually. EPRA was historically considered universally fatal due to associated pulmonary hypoplasia and neonatal respiratory failure. There are several etiologies of fetal renal failure that result in EPRA including bilateral renal agenesis, cystic kidney disease, and lower urinary tract obstruction. Appropriate sonographic evaluation is required to arrive at the appropriate urogenital diagnosis and to identify additional anomalies that allude to a specific genetic diagnosis. Genetic evaluation variably includes karyotype, microarray, targeted gene testing, panels, or whole exome sequencing depending on presentation. Patients receiving a fetal diagnosis of EPRA should be offered management options of pregnancy termination or perinatal palliative care, with the option of serial amnioinfusion therapy offered on a research basis. Preliminary data from case reports demonstrate an association between serial amnioinfusion therapy and short-term postnatal survival of EPRA, with excellent respiratory function in the neonatal period. A multicenter trial, the renal anhydramnios fetal therapy (RAFT) trial, is underway. We sought to review the initial diagnosis ultrasound findings, genetic etiologies, and current management options for EPRA.

Maturity-Onset Diabetes of the Young Identified Among Algerian Probands with Early-Onset Diabetes

AIM

To investigate the prevalence of variants within selected maturity-onset diabetes of the young (MODY)-genes among Algerian patients initially diagnosed with type 1 diabetes (T1D) or type 2 diabetes (T2D), yet presenting with a MODY-like phenotype.

METHODS

Eight unrelated patients with early-onset diabetes (before 30 years) and six relatives with diabetes were examined by targeted re-sequencing for variants in genes known to be involved in MODY (HNF1A, GCK, HNF4A, HNF1B, INS, ABCC8, KCNJ1). Clinical data for probands were retrieved from hospital records.

RESULTS

A total of 12 variants were identified, of which three were classified as pathogenic and one as a variant of uncertain clinical significance (VUS). Two of the pathogenic variants were found in GCK (p.Gly261Arg and p.Met210Lys, respectively) in one proband each and the remaining pathogenic variant was found in HNF1B (p.Gly76Cys) in a proband also carrying the VUS in HNF1A (p.Thr156Met).

CONCLUSION

Variants in known MODY-genes can be the cause of early-onset diabetes in Algerians diagnosed with T1D or T2D among patients presenting with a MODY-like phenotype; thus, genetic screening should be considered.

Intrauterine low-protein diet aggravates developmental abnormalities of the urinary system via the Akt/Creb3 pathway in Robo2 mutant mice

The offspring of Robo2 mutant mice usually present with variable phenotypes of congenital anomalies of the kidney and urinary tract (CAKUT). An intrauterine low-protein diet can also cause CAKUT in offspring, dominated by the duplicated collecting system phenotype. A single genetic or environment factor can only partially explain the pathogenesis of CAKUT. The present study aimed to establish an intrauterine low-protein diet roundabout 2 (Robo2) mutant mouse model and found that the intrauterine low-protein diet led to significantly increased CAKUT phenotypes in Robo2^PB/+ mice offspring, dominant by a duplicated collecting system. At the same time, more ectopic and lower located ureteric buds (UBs) were observed in the intrauterine low-protein diet-fed Robo2 mutant mouse model, and the number of UB branches was reduced in the serum-free culture. During UB protrusion, intrauterine low-protein diet reduced the expression of Slit2/Robo2 in Robo2 mutant mice and affected the expression of glial cell-derived neurotrophic factor/Ret, which is a key molecule for metanephric development, with increasing phospho-Akt and phospho-cAMP responsive element-binding protein 3 activity and a reduction of apoptotic cells in embryonic day 11.5 UB tissues. The mechanism by which an intrauterine low-protein diet aggravates CAKUT in Robo2 mutant mice may be related to the disruption of Akt/cAMP responsive element-binding protein 3 signaling and a reduction in apoptosis in UB tissue.

Prenatal diagnosis of HNF1B-associated renal cysts: Is there a need to differentiate intragenic variants from 17q12 microdeletion syndrome?

OBJECTIVE

17q12 microdeletions containing HNF1B and intragenic variants within this gene are associated with variable developmental, endocrine, and renal anomalies, often already noted prenatally as hyperechogenic/cystic kidneys. Here, we describe prenatal and postnatal phenotypes of seven individuals with HNF1B aberrations and compare their clinical and genetic data to those of previous studies.

METHODS

Prenatal sequencing and postnatal chromosomal microarray analysis were performed in seven individuals with renal and/or neurodevelopmental phenotypes. We evaluated HNF1B-related clinical features from 82 studies and reclassified 192 reported intragenic HNF1B variants.

RESULTS

In a prenatal case, we identified a novel in-frame deletion p.(Gly239del) within the HNF1B DNA-binding domain, a mutational hot spot as demonstrated by spatial clustering analysis and high computational prediction scores. The six postnatally diagnosed individuals harbored 17q12 microdeletions. Literature screening revealed variable reporting of HNF1B-associated clinical traits. Overall, both mutation groups showed a high phenotypic heterogeneity. The reclassification of all previously reported intragenic HNF1B variants provided an up-to-date overview of the mutational spectrum.

CONCLUSIONS

We highlight the value of prenatal HNF1B screening in renal developmental diseases. Standardized clinical reporting and systematic classification of HNF1B variants are necessary for a more accurate risk quantification of prenatal and postnatal clinical features, improving genetic counseling and prenatal decision making.

Prenatal genetic considerations of congenital anomalies of the kidney and urinary tract (CAKUT)

Congenital anomalies of the kidney and urinary tract (CAKUT) constitute 20% of all congenital malformations occurring in one in 500 live births. Worldwide, CAKUT are responsible for 40% to 50% of pediatric and 7% of adult end-stage renal disease. Pathogenic variants in genes causing CAKUT include monogenic diseases such as polycystic kidney disease and ciliopathies, as well as syndromes that include isolated kidney disease in conjunction with other abnormalities. Prenatal diagnosis most often occurs using ultrasonography; however, further genetic diagnosis may be made using a variety of testing strategies. Family history and pathologic examination can also provide information to improve the ability to make a prenatal diagnosis of CAKUT. Here, we provide a comprehensive overview of genetic considerations in the prenatal diagnosis of CAKUT disorders. Specifically, we discuss monogenic causes of CAKUT, associated ultrasound characteristics, and considerations for genetic diagnosis, antenatal care, and postnatal care.

New insights into the role of HNF-1β in kidney (patho)physiology

Hepatocyte nuclear factor-1β (HNF-1β) is an essential transcription factor that regulates the development and function of epithelia in the kidney, liver, pancreas, and genitourinary tract. Humans who carry HNF1B mutations develop heterogeneous renal abnormalities, including multicystic dysplastic kidneys, glomerulocystic kidney disease, renal agenesis, renal hypoplasia, and renal interstitial fibrosis. In the embryonic kidney, HNF-1β is required for ureteric bud branching, initiation of nephrogenesis, and nephron segmentation. Ablation of mouse Hnf1b in nephron progenitors causes defective tubulogenesis, whereas later inactivation in elongating tubules leads to cyst formation due to downregulation of cystic disease genes, including Umod, Pkhd1, and Pkd2. In the adult kidney, HNF-1β controls the expression of genes required for intrarenal metabolism and solute transport by tubular epithelial cells. Tubular abnormalities observed in HNF-1β nephropathy include hyperuricemia with or without gout, hypokalemia, hypomagnesemia, and polyuria. Recent studies have identified novel post-transcriptional and post-translational regulatory mechanisms that control HNF-1β expression and activity, including the miRNA cluster miR17 ∼ 92 and the interacting proteins PCBD1 and zyxin. Further understanding of the molecular mechanisms upstream and downstream of HNF-1β may lead to the development of new therapeutic approaches in cystic kidney disease and other HNF1B-related renal diseases.

Association between the clinical presentation of congenital anomalies of the kidney and urinary tract (CAKUT) and gene mutations: an analysis of 66 patients at a single institution

BACKGROUND

The association between the clinical presentation of congenital anomalies of the kidney and urinary tract (CAKUT) and gene mutations has yet to be fully explored.

METHODS

In this retrospective cohort study, we examined patients with CAKUT who underwent gene analysis. The analysis was performed in patients with bilateral renal lesions, extrarenal complications, or a family history of renal disease. The data from the diagnosis, gene mutations, and other complications were analyzed.

RESULTS

In total, 66 patients with CAKUT were included. Of these, gene mutations were detected in 14 patients. Bilateral renal lesions were significantly related to the identification of gene mutations (p = 0.02), and no gene mutations were observed in patients with lower urinary tract obstruction (six patients). There was no significant difference in the rate of gene mutations between those with or without extrarenal complications (p = 0.76). The HNF1β gene mutation was identified in most of the patients with hypodysplastic kidney with multicystic dysplastic kidney (six of seven patients). There was no significant difference in the presence or absence of gene mutations with respect to the renal survival rate (log-rank test p = 0.53). The renal prognosis varied, but the differences were not statistically significant for any of the gene mutations.

CONCLUSIONS

CAKUT with bilateral renal lesions were significantly related to gene mutations. We recommend that CAKUT-related gene analysis be considered in cases of bilateral renal lesions. No gene mutations were observed in patients with lower urinary tract obstruction. The renal prognosis varied for each gene mutation.

Negative autoimmunity in a Spanish pediatric cohort suspected of type 1 diabetes, could it be monogenic diabetes?

Objective

Monogenic diabetes can be misdiagnosed as type 1 or type 2 diabetes in children. The right diagnosis is crucial for both therapeutic choice and prognosis and influences genetic counseling. The main objective of this study was to search for monogenic diabetes in Spanish pediatric patients suspected of type 1 diabetes with lack of autoimmunity at the onset of the disease. We also evaluated the extra value of ZnT8A in addition to the classical IAA, GADA and IA2A autoantibodies to improve the accuracy of type 1 diabetes diagnosis.

Methods

Four hundred Spanish pediatric patients with recent-onset diabetes (mean age 8.9 ± 3.9 years) were analyzed for IAA, GADA, IA2A and ZnT8A pancreatic-autoantibodies and HLA-DRB1 alleles. Patients without autoimmunity and those with only ZnT8A positive were screened for 12 monogenic diabetes genes by next generation sequencing.

Results

ZnT8A testing increased the number of autoantibody-positive patients from 373 (93.3%) to 377 (94.3%). An isolated positivity for ZnT8A allowed diagnosing autoimmune diabetes in 14.8% (4/27) of pediatric patients negative for the rest of the antibodies tested. At least 2 of the 23 patients with no detectable autoimmunity (8%) carried heterozygous pathogenic variants: one previously reported missense variant in the INS gene (p.Gly32Ser) and one novel frameshift variant (p.Val264fs) in the HNF1A gene. One variant of uncertain significance was also found. Carriers of pathogenic variants had HLA-DRB1 risk alleles for autoimmune diabetes and clinical characteristics compatible with type 1 diabetes except for the absence of autoimmunity.

Conclusion

ZnT8A determination improves the diagnosis of autoimmune diabetes in pediatrics. At least 8% of pediatric patients suspected of type 1 diabetes and with undetectable autoimmunity have monogenic diabetes and can benefit from the correct diagnosis of the disease by genetic study.

Clinical characteristics of HNF1B-related disorders in a Japanese population

BACKGROUND

Hepatocyte nuclear factor 1β (HNF1B), located on chromosome 17q12, causes renal cysts and diabetes syndrome (RCAD). Moreover, various phenotypes related to congenital anomalies of the kidney and urinary tract (CAKUT) or Bartter-like electrolyte abnormalities can be caused by HNF1B variants. In addition, 17q12 deletion syndrome presents with multi-system disorders, as well as RCAD. As HNF1B mutations are associated with different phenotypes and genotype-phenotype relationships remain unclear, here, we extensively studied these mutations in Japan.

METHODS

We performed genetic screening of RCAD, CAKUT, and Bartter-like syndrome cases. Heterozygous variants or whole-gene deletions in HNF1B were detected in 33 cases (19 and 14, respectively). All deletion cases were diagnosed as 17q12 deletion syndrome, confirmed by multiplex ligation probe amplification and/or array comparative genomic hybridization. A retrospective review of clinical data was also conducted.

RESULTS

Most cases had morphological abnormalities in the renal-urinary tract system. Diabetes developed in 12 cases (38.7%). Hyperuricemia and hypomagnesemia were associated with six (19.3%) and 13 cases (41.9%), respectively. Pancreatic malformations were detected in seven cases (22.6%). Ten patients (32.3%) had liver abnormalities. Estimated glomerular filtration rates were significantly lower in the patients with heterozygous variants compared to those in patients harboring the deletion (median 37.6 vs 58.8 ml/min/1.73 m²; p = 0.0091).

CONCLUSION

We present the clinical characteristics of HNF1B-related disorders. To predict renal prognosis and complications, accurate genetic diagnosis is important. Genetic testing for HNF1B mutations should be considered for patients with renal malformations, especially when associated with other organ involvement.

The copy number variation landscape of congenital anomalies of the kidney and urinary tract

Congenital anomalies of the kidney and urinary tract (CAKUT) are a major cause of pediatric kidney failure. We performed a genome-wide analysis of copy number variants (CNVs) in 2,824 cases and 21,498 controls. Affected individuals carried a significant burden of rare exonic (i.e. affecting coding regions) CNVs and were enriched for known genomic disorders (GD). Kidney anomaly (KA) cases were most enriched for exonic CNVs, encompassing GD-CNVs and novel deletions; obstructive uropathy (OU) had a lower CNV burden and an intermediate prevalence of GD-CNVs; vesicoureteral reflux (VUR) had the fewest GD-CNVs but was enriched for novel exonic CNVs, particularly duplications. Six loci (1q21, 4p16.1-p16.3, 16p11.2, 16p13.11, 17q12, and 22q11.2) accounted for 65% of patients with GD-CNVs. Deletions at 17q12, 4p16.1-p16.3, and 22q11.2 were specific for KA; the 16p11.2 locus showed extensive pleiotropy. Using a multidisciplinary approach, we identified TBX6 as a driver for the CAKUT subphenotypes in the 16p11.2 microdeletion syndrome.

Developmental pathology of congenital kidney and urinary tract anomalies

Congenital anomalies of the kidneys or lower urinary tract (CAKUT) are the most common causes of renal failure in children and account for 25% of end-stage renal disease in adults. The spectrum of anomalies includes renal agenesis; hypoplasia; dysplasia; supernumerary, ectopic or fused kidneys; duplication; ureteropelvic junction obstruction; primary megaureter or ureterovesical junction obstruction; vesicoureteral reflux; ureterocele; and posterior urethral valves. CAKUT originates from developmental defects and can occur in isolation or as part of other syndromes. In recent decades, along with better understanding of the pathological features of the human congenital urinary tract defects, researchers using animal models have provided valuable insights into the pathogenesis of these diseases. However, the genetic causes and etiology of many CAKUT cases remain unknown, presenting challenges in finding effective treatment. Here we provide an overview of the critical steps of normal development of the urinary system, followed by a description of the pathological features of major types of CAKUT with respect to developmental mechanisms of their etiology.

Variable phenotype in HNF1B mutations: extrarenal manifestations distinguish affected individuals from the population with congenital anomalies of the kidney and urinary tract

Background

Mutations in hepatocyte nuclear factor 1B (HNF1B) have been associated with congenital anomalies of the kidney and urinary tract (CAKUT) in humans. Diabetes and other less frequent anomalies have also been described. Variable penetrance and intrafamilial variability have been demonstrated including severe prenatal phenotypes. Thus, it is important to differentiate this entity from others with similar clinical features and perform confirmatory molecular diagnosis.

Methods

This study reports the results of HNF1B screening in a cohort of 60 patients from 58 unrelated families presenting with renal structural anomalies and/or non-immune glucose metabolism alterations, and other minor features suggesting HNF1B mutations.

Results

This study identified a pathogenic variant in 23 patients from 21 families. The most frequent finding was bilateral cystic dysplasia or hyperechogenic kidneys (87% of patients). Sixty percent of them also fulfilled the criteria for impaired glucose metabolism, and these were significantly older than those patients with an HNF1B mutation but without diabetes or prediabetes (14.4 versus 3.3 years, P < 0.05). Furthermore, patients with HNF1B mutations had higher frequency of pancreatic structural anomalies and hypomagnesaemia than patients without mutations (P < 0.001 and P = 0.003, respectively). Hyperuricaemia and increased liver enzymes were detected in some patients as well.

Conclusions

Renal anomalies found in patients with HNF1B mutations are frequently unspecific and may resemble those found in other renal pathologies (CAKUT, ciliopathies). Active searching for extrarenal minor features, especially pancreatic structural anomalies or hypomagnesaemia, could support the indication for molecular diagnosis to identify HNF1B mutations.

Polycystic kidney features of the renal pathology in glycogen storage disease type I: possible evolution to renal neoplasia

Glycogen storage disease type I (GSDI) is a rare genetic pathology characterized by glucose-6 phosphatase (G6Pase) deficiency, translating in hypoglycemia during short fasts. Besides metabolic perturbations, GSDI patients develop long-term complications, especially chronic kidney disease (CKD). In GSDI patients, CKD is characterized by an accumulation of glycogen and lipids in kidneys, leading to a gradual decline in renal function. At a molecular level, the activation of the renin-angiotensin system is responsible for the development of renal fibrosis, eventually leading to renal failure. The same CKD phenotype was observed in a mouse model with a kidney-specific G6Pase deficiency (K.G6pc-/- mice). Furthermore, GSDI patients and mice develop frequently renal cysts at late stages of the nephropathy, classifying GSDI as a potential polycystic kidney disease (PKD). PKDs are genetic disorders characterized by multiple renal cyst formation, frequently caused by the loss of expression of polycystic kidney genes, such as PKD1/2 and PKHD1. Interestingly, these genes are deregulated in K.G6pc-/- kidneys, suggesting their possible role in GSDI cystogenesis. Finally, renal cysts are known to predispose to renal malignancy development. In addition, HNF1B loss is a malignancy prediction factor. Interestingly, Hnf1b expression was decreased in K.G6pc-/- kidneys. While a single case of renal cancer has been reported in a GSDI patient, a clear cell renal carcinoma was recently observed in one K.G6pc-/- mouse (out of 36 studied mice) at a later stage of the disease. This finding highlights the need to further analyze renal cyst development in GSDI patients in order to evaluate the possible associated risk of carcinogenesis, even if the risk might be limited.

Genome-wide methylomic analysis in individuals with HNF1B intragenic mutation and 17q12 microdeletion

Heterozygous mutation of the transcription factor HNF1B is the most common cause of monogenetic developmental renal disease. Disease-associated mutations fall into two categories: HNF1B intragenic mutations and a 1.3 Mb deletion at chromosome 17q12. An increase in neurodevelopmental disorders has been observed in individuals harbouring the 17q12 deletion but not in patients with HNF1B coding mutations.Previous investigations have concentrated on identifying a genetic cause for the increase in behavioural problems seen in 17q12 deletion carriers. We have taken the alternative approach of investigating the DNA methylation profile of these two HNF1B genotype groups along with controls matched for age, gender and diabetes status using the Illumina 450K DNA methylation array (total sample n = 60).We identified a number of differentially methylated probes (DMPs) that were associated with HNF1B-associated disease and passed our stringent experiment-wide significance threshold. These associations were largely driven by the deletion patients and the majority of the significant probes mapped to the 17q12 deletion locus. The observed changes in DNA methylation at this locus were not randomly dispersed and occurred in clusters, suggesting a regulatory mechanism reacting to haploinsufficiency across the entire deleted region.Along with these deletion-specific changes in DNA methylation, we also identified a shared DNA methylation signature in both mutation and deletion patient groups indicating that haploinsufficiency of HNF1B impacts on the methylome of a number of genes, giving further insight to the role of HNF1B.

Targeted gene sequencing and whole-exome sequencing in autopsied fetuses with prenatally diagnosed kidney anomalies

Identification of fetal kidney anomalies invites questions about underlying causes and recurrence risk in future pregnancies. We therefore investigated the diagnostic yield of next-generation sequencing in fetuses with bilateral kidney anomalies and the correlation between disrupted genes and fetal phenotypes. Fetuses with bilateral kidney anomalies were screened using an in-house-designed kidney-gene panel. In families where candidate variants were not identified, whole-exome sequencing was performed. Genes uncovered by this analysis were added to our kidney panel. We identified likely deleterious variants in 11 of 56 (20%) families. The kidney-gene analysis revealed likely deleterious variants in known kidney developmental genes in 6 fetuses and TMEM67 variants in 2 unrelated fetuses. Kidney histology was similar in the latter 2 fetuses-presenting a distinct prenatal form of nephronophthisis. Exome sequencing identified ROBO1 variants in one family and a GREB1L variant in another family. GREB1L and ROBO1 were added to our kidney-gene panel and additional variants were identified. Next-generation sequencing substantially contributes to identifying causes of fetal kidney anomalies. Genetic causes may be supported by histological examination of the kidneys. This is the first time that SLIT-ROBO signaling is implicated in human bilateral kidney agenesis.

De novo HNF1 homeobox B mutation as a cause for chronic, treatment-resistant hypomagnesaemia

29-year-old female presenting with an 8-year history of unexplained hypomagnesaemia, which was severe enough to warrant intermittent inpatient admission for intravenous magnesium. Urinary magnesium was inappropriately normal in the context of hypomagnesaemia indicating magnesium wasting. Ultrasound imaging demonstrated unilateral renal cysts and computed tomography of kidneys, ureters and bladder showed a bicornuate uterus. Referral to genetic services and subsequent testing revealed a de novo HNF1B deletion.

Exocrine pancreatic dysfunction is common in hepatocyte nuclear factor 1β-associated renal disease and can be symptomatic

Background

Heterozygous mutations in the HNF1B gene are the most common monogenic cause of developmental kidney disease. Extrarenal phenotypes frequently occur, including diabetes mellitus and pancreatic hypoplasia; the latter is associated with subclinical exocrine dysfunction. We measured faecal elastase-1 in patients with HNF1B-associated disease regardless of diabetes status and assessed the degree of symptoms associated with pancreatic exocrine deficiency.

Methods

Faecal elastase-1 was measured in 29 patients with a known HNF1B mutation. We defined a low faecal elastase-1 concentration based on the 2.5 percentile of 99 healthy control individuals (410 μg/g stool). Symptoms related to pancreatic exocrine dysfunction were assessed and a subset of the HNF1B cohort (n  =  6) underwent pancreatic imaging.

Results

Faecal elastase-1 was below the 2.5 percentile of the control cohort in 18/29 (62%) patients with HNF1B-associated renal disease. A total of 8/29 (28%) had a measurement suggestive of exocrine pancreatic insufficiency at  <200 μg/g stool; of these, 3 suffered with abdominal pain, loose stools and/or unintentional weight loss. All three experienced symptomatic improvement and weight gain after commencing pancreatic enzyme replacement therapy. Faecal elastase-1 was low in 7/15 (47%) HNF1B patients without diabetes compared with 11/14 (79%) of those with diabetes (P  =  0.1).

Conclusions

Faecal elastase-1 deficiency is a common feature of HNF1B-associated renal disease even when diabetes is not present and pancreatic exocrine deficiency may be more symptomatic than previously suggested. Faecal elastase-1 should be measured in all patients with known HNF1B-associated disease complaining of chronic abdominal pain, loose stools or unintentional weight loss. The discovery of a low faecal elastase-1 concentration in individuals with developmental kidney disease of uncertain cause should prompt referral for HNF1B genetic testing.

Genetic basis of human congenital anomalies of the kidney and urinary tract

The clinical spectrum of congenital anomalies of the kidney and urinary tract (CAKUT) encompasses a common birth defect in humans that has significant impact on long-term patient survival. Overall, data indicate that approximately 20% of patients may have a genetic disorder that is usually not detected based on standard clinical evaluation, implicating many different mutational mechanisms and pathogenic pathways. In particular, 10% to 15% of CAKUT patients harbor an unsuspected genomic disorder that increases risk of neurocognitive impairment and whose early recognition can impact clinical care. The emergence of high-throughput genomic technologies is expected to provide insight into the common and rare genetic determinants of diseases and offer opportunities for early diagnosis with genetic testing.

Targeted Exome Sequencing Identifies PBX1 as Involved in Monogenic Congenital Anomalies of the Kidney and Urinary Tract

Congenital anomalies of the kidney and urinary tract (CAKUT) occur in three to six of 1000 live births, represent about 20% of the prenatally detected anomalies, and constitute the main cause of CKD in children. These disorders are phenotypically and genetically heterogeneous. Monogenic causes of CAKUT in humans and mice have been identified. However, despite high-throughput sequencing studies, the cause of the disease remains unknown in most patients, and several studies support more complex inheritance and the role of environmental factors and/or epigenetics in the pathophysiology of CAKUT. Here, we report the targeted exome sequencing of 330 genes, including genes known to be involved in CAKUT and candidate genes, in a cohort of 204 unrelated patients with CAKUT; 45% of the patients were severe fetal cases. We identified pathogenic mutations in 36 of 204 (17.6%) patients. These mutations included five de novo heterozygous loss of function mutations/deletions in the PBX homeobox 1 gene (PBX1), a gene known to have a crucial role in kidney development. In contrast, the frequency of SOX17 and DSTYK variants recently reported as pathogenic in CAKUT did not indicate causality. These findings suggest that PBX1 is involved in monogenic CAKUT in humans and call into question the role of some gene variants recently reported as pathogenic in CAKUT. Targeted exome sequencing also proved to be an efficient and cost-effective strategy to identify pathogenic mutations and deletions in known CAKUT genes.

Genetics of vesicoureteral reflux and congenital anomalies of the kidney and urinary tract

The definition of congenital anomalies of the kidney and urinary tract (CAKUT) is the disease of structural malformations in the kidney and/or urinary tract containing vesicoureteral reflux (VUR). These anomalies can cause pediatric chronic kidney disease. However, the pathogenesis of CAKUT is not well understood, because identifying the genetic architecture of CAKUT is difficult due to the phenotypic heterogeneity and multifactorial genetic penetrance. We describe the current genetic basis and mechanisms of CAKUT including VUR via approaching the steps and signaling pathways of kidney developmental processes. We also focus on the newly developed strategies and challenges to fully address the role of the associated genes in the pathogenesis of the disease.

Genetics of Congenital Anomalies of the Kidney and Urinary Tract: The Current State of Play

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most frequent form of malformation at birth and represent the cause of 40–50% of pediatric and 7% of adult end-stage renal disease worldwide. The pathogenesis of CAKUT is based on the disturbance of normal nephrogenesis, secondary to environmental and genetic causes. Often CAKUT is the first clinical manifestation of a complex systemic disease, so an early molecular diagnosis can help the physician identify other subtle clinical manifestations, significantly affecting the management and prognosis of patients. The number of sporadic CAKUT cases explained by highly penetrant mutations in a single gene may have been overestimated over the years and a genetic diagnosis is missed in most cases, hence the importance of identifying new genetic approaches which can help unraveling the vast majority of unexplained CAKUT cases. The aim of our review is to clarify the current state of play and the future perspectives of the genetic bases of CAKUT.