Clinical and genetic variability of PAX2-related disorder in the Japanese population

Practical Approach to Congenital Anomalies of the Kidneys: Focus on Anomalies With Insufficient or Abnormal Nephron Development: Renal Dysplasia, Renal Hypoplasia, and Renal Tubular Dysgenesis

Congenital anomalies of the kidney and urinary tract (CAKUT) accounts for up to 30% of antenatal congenital anomalies and is the main cause of kidney failure in children worldwide. This review focuses on practical approaches to CAKUT, particularly those with insufficient or abnormal nephron development, such as renal dysplasia, renal hypoplasia, and renal tubular dysgenesis. The review provides insights into the histological features, pathogenesis, mechanisms, etiologies, antenatal and postnatal presentation, management, and prognosis of these anomalies. Differential diagnoses are discussed as several syndromes may include CAKUT as a phenotypic component and renal dysplasia may occur in some ciliopathies, tumor predisposition syndromes, and inborn errors of metabolism. Diagnosis and genetic counseling for CAKUT are challenging, due to the extensive variability in presentation, genetic and phenotypic heterogeneity, and difficulties to assess postnatal lung and renal function on prenatal imaging. The review highlights the importance of perinatal autopsy and pathological findings in surgical specimens to establish the diagnosis and prognosis of CAKUT. The indications and the type of genetic testing are discussed. The aim is to provide essential insights into the practical approaches, diagnostic processes, and genetic considerations offering valuable guidance for pediatric and perinatal pathologists.

Deciphering the etiology of undiagnosed ocular anomalies along with systemic alterations in pediatric patients through whole exome sequencing

Inherited and developmental eye diseases are quite diverse and numerous, and determining their genetic cause is challenging due to their high allelic and locus heterogeneity. New molecular approaches, such as whole exome sequencing (WES), have proven to be powerful molecular tools for addressing these cases. The present study used WES to identify the genetic etiology in ten unrelated Mexican pediatric patients with complex ocular anomalies and other systemic alterations of unknown etiology. The WES approach allowed us to identify five clinically relevant variants in the GZF1, NFIX, TRRAP, FGFR2 and PAX2 genes associated with Larsen, Malan, developmental delay with or without dysmorphic facies and autism, LADD1 and papillorenal syndromes. Mutations located in GZF1 and NFIX were classified as pathogenic, those in TRRAP and FGFR2 were classified as likely pathogenic variants, and those in PAX2 were classified as variants of unknown significance. Protein modeling of the two missense FGFR2 p.(Arg210Gln) and PAX2 p.(Met3Thr) variants showed that these changes could induce potential structural alterations in important functional regions of the proteins. Notably, four out of the five variants were not previously reported, except for the TRRAP gene. Consequently, WES enabled the identification of the genetic cause in 40% of the cases reported. All the syndromes reported herein are very rare, with phenotypes that may overlap with other genetic entities.

Impaired neural circuitry of hippocampus in Pax2 nervous system-specific knockout mice leads to restricted repetitive behaviors

INTRODUCTION

Restricted repetitive behaviors (RRBs), which are associated with many different neurological and mental disorders, such as obsessive-compulsive disorder (OCD) and autism, are patterns of behavior with little variation and little obvious function. Paired Box 2 (Pax2) is a transcription factor that is expressed in many systems, including the kidney and the central nervous system. The protein that is encoded by Pax2 has been implicated in the development of the nervous system and neurodevelopmental disorders. In our previous study, Pax2 heterozygous gene knockout mice (Pax2+/- mice) showed abnormally increased self-grooming and impaired learning and memory abilities. However, it remains unclear which cell type is involved in this process. In this study, we deleted Pax2 only in the nervous system to determine the regulatory mechanism of Pax2 in RRBs.

METHODS

In this study, Pax2 nervous system-specific knockout mice (Nestin-Pax2 mice) aged 6-8 weeks and Pax2 flox mice of the same age were recruited as the experimental group. Tamoxifen and vehicle were administered via intraperitoneal injection to induce Pax2 knockout after gene identification. Western blotting was used to detect Pax2 expression. After that, we assessed the general health of these two groups of mice. The self-grooming test, marble burying test and T-maze acquisition and reversal learning test were used to observe the lower-order and higher-order RRBs. The three-chamber test, Y-maze, and elevated plus-maze were used to assess social ability, spatial memory ability, and anxiety. Neural circuitry tracing and transcriptome sequencing (RNA-seq) were used to observe the abnormal neural circuitry, differentially expressed genes (DEGs) and signaling pathways affected by Pax2 gene knockout in the nervous system and the putative molecular mechanism.

RESULTS

(1) The Nestin-Pax2 mouse model was successfully constructed, and the Nestin-Pax2 mice showed decreased expression of Pax2. (2) Nestin-Pax2 mice showed increased self-grooming behavior and impaired T-maze reversal behavior compared with Pax2 flox mice. (3) An increased number of projection fibers can be found in the mPFC projecting to the CA1 and BLA, and a reduction in IGFBP2 can be found in the hippocampus of Nestin-Pax2 mice.

CONCLUSION

The results demonstrated that loss of Pax2 in the nervous system leads to restricted repetitive behaviors. The mechanism may be associated with impaired neural circuitry and a reduction in IGFBP2.

Ocular manifestations of the genetic causes of focal and segmental glomerulosclerosis

Genetic forms of focal and segmental glomerulosclerosis (FSGS) often have extra-renal manifestations. This study examined FSGS-associated genes from the Genomics England Renal proteinuria panel for reported and likely ocular features. Thirty-two of the 55 genes (58%) were associated with ocular abnormalities in human disease, and a further 12 (22%) were expressed in the retina or had an eye phenotype in mouse models. The commonest genes affected in congenital nephrotic syndrome (NPHS1, NPHS2, WT1, LAMB2, PAX2 but not PLCE1) may have ocular manifestations . Many genes affected in childhood-adolescent onset FSGS (NPHS1, NPHS2, WT1, LAMB2, SMARCAL1, NUP107 but not TRPC6 or PLCE1) have ocular features. The commonest genes affected in adult-onset FSGS (COL4A3-COL4A5, GLA ) have ocular abnormalities but not the other frequently affected genes (ACTN4, CD2AP, INF2, TRPC6). Common ocular associations of genetic FSGS include cataract, myopia, strabismus, ptosis and retinal atrophy. Mitochondrial forms of FSGS (MELAS, MIDD, Kearn's Sayre disease) are associated with retinal atrophy and inherited retinal degeneration. Some genetic kidney diseases (CAKUT, ciliopathies, tubulopathies) that result in secondary forms of FSGS also have ocular features. Ocular manifestations suggest a genetic basis for FSGS, often help identify the affected gene, and prompt genetic testing. In general, ocular abnormalities require early evaluation by an ophthalmologist, and sometimes, monitoring or treatment to improve vision or prevent visual loss from complications. In addition, the patient should be examined for other syndromic features and first degree family members assessed.

PAX2 Gene Mutation in Pediatric Renal Disorders-A Narrative Review

The PAX2 gene is a transcription factor that is essential for the development of the urinary system among other transcription factors. The role of PAX2 is highlighted from the seventh week of gestation, when it is involved in development processes and the emergence of nephrons and collecting tubes. Being an important factor in renal development, mutations of this gene can produce severe alterations in the development of the urinary tract, namely congenital anomalies of the kidneys and urinary tract. The first reported cases described with the PAX2 mutation included both renal anomalies and the involvement of other organs, such as the eyes, producing renal coloboma syndrome. Over the years, numerous cases have been reported, including those with only renal and urinary tract anomalies. The aim of this review is to present a summary of pediatric patients described to have mutations in the PAX2 gene to contribute to a better understanding of the genetic mechanism causing anomalies of the kidneys and urinary tract. In this review, we have included only pediatric cases with renal and urinary tract disorders, without the involvement of other organs. From what we know so far from the literature, this is the first review gathering pediatric patients presenting the PAX2 mutation who have been diagnosed exclusively with renal and urinary tract disorders.

Renal Coloboma Syndrome – An Autosomal Dominant Genetic Disorder

Renal coloboma syndrome is an autosomal dominant genetic disorder that primarily affects kidney and eye development. It is also known as papillorenal syndrome. People with this condition typically have kidneys that are small and underdeveloped (hypodysplastic), which can lead to end-stage renal disease. It has been estimated that approximately 10% of children with hypoplastic kidneys may have renal coloboma syndrome. The eye anomalies consist of a wide and dysplastic optic disk with the emergence of the retinal vessels from the periphery of the disk, frequently called optic nerve coloboma.

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.

Decreased Microglia in Pax2 Mutant Mice Leads to Impaired Learning and Memory

Impaired learning and memory ability is one of the characteristics of a variety of neurological diseases, and its molecular mechanisms are complex and diverse and are regulated by a variety of factors. It is generally believed that synaptic plasticity plays an important role in the process of learning and memory. The protein encoded by the Pax2 gene is a transcription factor involved in neuron migration and cell fate determination during neural development. Mice knocked out of BDNF in the Pax2 lineage-derived interneuron precursor exhibited learning disabilities and severe cognitive impairment. In this study, Pax2 heterozygous gene (Pax2^+/- mice) deletion mice were used as the research objects and behavioral tests were used to observe the effect of Pax2 gene deletion on learning and memory ability; morphological and molecular biological methods were used to observe the effect of Pax2 gene deletion on the neural structure. Single-cell transcriptome sequencing was used to observe the cell subtypes and differentially expressed genes (DEGs) and signaling pathways affected by Pax2 gene deletion and the possible molecular mechanisms. The results showed that Pax2^+/- mice had impaired learning and memory ability, abnormal synaptic structure, and significantly reduced number of microglia clusters, and DEGs were associated with pro-inflammatory chemokines. Finally, we speculate that Pax2 gene deletion may lead to abnormal chemokines and chemokine receptors by affecting microglia.

Detection of De Novo PAX2 Variants and Phenotypes in Chinese Population: A Single-Center Study

Background:PAX2 is a nuclear transcription factor gene that is highly conserved among species. Variants within PAX2 could result in optic nerve colobomas and kidney hypoplasia. However, little clinical and genetic information is currently available about PAX2 variants in Chinese children.

Objective: This study aims to further understand the clinical manifestations and genetic characteristics of PAX2 variants in Chinese population.

Methods: In this single-center retrospective study, we analyzed the clinical data of 10 children identified as carriers of PAX2 variants by gene sequencing. All the variants found in this study were analyzed using in silico prediction and American College of Medical Genetics and Genomics (ACMG) standards and guidelines.

Results: The mean age for developing the first symptom in 10 unrelated children was 7.2 years old. Proteinuria and bilateral kidney dysplasia were found in every patient. Two children underwent kidney histological examination; one child showed high-intensity C1q deposition in the kidney, and the other child showed focal segmental glomerular sclerosis (FSGS). Three children had PAX2-related ocular abnormalities, including nystagmus, retinal exudation, amblyopia, microphthalmia, microcornea, and total blindness. In addition, one patient had the comorbidity of oculocutaneous albinism (OCA). Eight different PAX2 variants were found in ten patients, three of which were reported for the first time.

Conclusion: We reported some patients with unique manifestations and comorbidities, and we reported three variants that have not been previously identified. The PAX2 gene is prone to spontaneous variants, and the outcome of patients is unfavorable. Because of the lack of specific therapy, genetic testing should be recommended for individuals with obvious evidence of kidney dysplasia and eye abnormalities, and kidney protective treatment should be initiated early.

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.

Phenotypic spectrum and genetics of PAX2-related disorder in the Chinese cohort

Background

Pathogenic variants of PAX2 cause autosomal-dominant PAX2-related disorder, which includes variable phenotypes ranging from renal coloboma syndrome (RCS), congenital anomalies of the kidney and urinary tract (CAKUT) to nephrosis. Phenotypic variability makes it difficult to define the phenotypic spectrum associated with genotype.

Methods

We collected the phenotypes in patients enrolled in the China national multicenter registry who were diagnosed with pathogenic variant in PAX2 and reviewed all published cases with PAX2-related disorders. We conducted a phenotype-based cluster analysis by variant types and molecular modeling of the structural impact of missense variants.

Results

Twenty different PAX2 pathogenic variants were identified in 32 individuals (27 families) with a diagnosis of RCS (9), CAKUT (11) and nephrosis (12) from the Chinese cohort. Individuals with abnormal kidney structure (RCS or CAKUT group) tended to have likely/presumed gene disruptive (LGD) variants (Fisher test, p < 0.05). A system review of 234 reported cases to date indicated a clear association of RCS to heterozygous loss-of-function PAX2 variants (LGD variants). Furthermore, we identified a subset of PAX2 missense variants in DNA-binding domain predicted to affect the protein structure or protein-DNA interaction associated with the phenotype of RCS.

Conclusion

Defining the phenotypic spectrum combined with genotype in PAX2-related disorder allows us to predict the pathogenic variants associated with renal and ophthalmological development. It highlighted the approach of structure-based analysis can be applied to diagnostic strategy aiding precise and timely diagnosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-021-01102-x.

A novel PAX2 heterozygous mutation in a family with Papillorenal syndrome: A case report and review of the literature

Purpose

Papillorenal syndrome (PAPRS) is a rare inherited disorder often involves abnormalities of eye and kidney. Paired box 2 (PAX2) gene, which is widely expressed in the development of the organs including kidney, ureter, eye, ear, and central nervous system has been considered an underlying cause of PAPRS. The present work aims to further our understanding of PAX2 gene and PAPRS by reporting a family with PAPRS associated with a novel PAX2 mutation and describing ocular manifestation of PAX2 mutation in previous literatures.

Observation

We herein present a family with PAPRS presented with typical congenital optic disc defects and mild renal dysplasia. Through screening of candidate genes based on the next-generation sequencing, the heterozygous PAX2 mutation c.175C > T (p. Arg59Trp) was identified which had never been reported.

Conclusions

The study expands the genetic and clinic spectrum of PAPRS. Further review of detailed ocular manifestation and genotypes of PAX2 mutation in previous study improves the recognition of the ocular phenotypes' spectrum, assists in the identification of PAPRS. Moreover, this study reveals that PAPRS is a systemic disorder with heterogeneous diverse phenotypes, and shows the importance of gene panel sequencing in the diagnosis of PAPRS which could achieve high diagnostic rates.

The Role of PAX2 in Neurodevelopment and Disease

In developmental biology, transcription factors are involved in regulating the process of neural development, controlling the differentiation of nerve cells, and affecting the normal functioning of neural circuits. Transcription factors regulate the expression of multiple genes at the same time and have become a key gene category that is recognized to be disrupted in neurodevelopmental disorders such as autism spectrum disorders. This paper briefly introduces the expression and role of PAX2 in neurodevelopment and discusses the neurodevelopmental disorders associated with Pax2 mutations and its possible mechanism. Firstly, mutations in the human Pax2 gene are associated with abnormalities in multiple systems which can result in neurodevelopmental disorders such as intellectual disability, epilepsy and autism spectrum disorders. Secondly, the structure of Pax2 gene and PAX2 protein, as well as the function of Pax2 gene in neural development, was discussed. Finally, a diagram of the PAX2 protein regulatory network was made and a possible molecular mechanism of Pax2 mutations leading to neurodevelopmental disorders from the perspectives of developmental process and protein function was proposed.

PAX2 Mutation-Related Renal Hypodysplasia: Review of the Literature and Three Case Reports

Paired box 2 (PAX2)-related disorder is an autosomal dominant genetic disorder associated with kidney and eye abnormalities and can result in end stage renal disease (ESRD). Despite reported low prevalence of PAX2 mutations, the prevalence of PAX2 related disorders may have been underestimated in past studies. With improved genetic sequencing techniques, more genetic abnormalities are being detected than ever before. Here, we report three patients from two families with PAX2 mutations identified within 1 year. Two patients were adults with chronic kidney disease and were followed for decades without correct diagnoses, including one with ESRD who had even undergone kidney transplant. The third patient was a neonate in whom PAX2-related disorder manifested as oligohydramnios, coloboma, and renal failure that progressed to ESRD within 1 year after birth. The phenotypes of PAX2 gene mutation were shown to be highly variable, even within the same family. Early detection promoted genetic counseling and guided clinical management. The appropriate time point for genetic study is an important issue. Clinicians must be more alert for PAX2 mutation when facing patients with congenital kidney and urinary tract anomalies, chronic kidney disease of unknown etiology, involvement of multiple systems, and/or a family history of renal disease.

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.