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.

Egyptian pediatric clinical practice guidelines for urinary tract infections in infants and children (evidence based)

Background National evidence-based recommendations for diagnosis, treatment, imaging, and follow-up in urinary tract infection are crucial being a major health problem in pediatrics. Every region should follow international recommendations with respect to the disease local profile and available facilities for that area. Methods Based on AGREE II (the assessment tool of practice guidelines), Egyptian CGLs used *American Academy Pediatrics, *European Association Urology, European Society Pediatric Urology, and *Asian Association Urinary tract infections as its evidence-based references. Health questions were listed for evidence base answers adopted from selected CGLs after their permission. Key statements were approved by all members and further approved by the Egyptian Pediatric Guidelines Committee after local and international external peer reviewing. Results (1) Diagnosis recommendations: Urine culture with diagnostic colony counts is essential for diagnosis. Catheter samples are important for critical cases and non-toilet-trained cases especially when they show significant bacteriuria and pyuria. (2) Treatment plan included areas of debate as choice of antibiotic, oral versus intravenous, duration, antibiotic prophylaxis considering age, disease severity, recurrence, + risk factors, and imaging reports. (3) Imaging recommendations were tailored to suit our community. Renal bladder ultrasound is important for children with febrile UTI, due to the high prevalence of congenital anomalies of the kidney and urinary tract, paucity of prenatal ultrasound, and lack of medical documentation to reflect previously diagnosed UTI or US reports. We recommend renal isotopic scan and voiding cystography for serious presentation, high-risk factors, recurrence, and abnormal US. (4) Urological consultation is recommended: in urosepsis or obstruction, male infants < 6 months. Acute basal DMSA is recommended in congenital renal hypodysplasia. Six months post-infection, US and DMSA are recommended in severe pyelonephritis and vesico-ureteric reflux, where those with abnormal US or DMSA or both should have voiding cystography. (5) Follow-up recommendations include family orientation with hazards of noncompliance and monitoring at pregnancy. Conclusion Diagnosis and treatment show strong recommendations. Imaging depends on patient assessment. Referral to a pediatric nephrologist and urologist in complicated cases is crucial. Follow-up after the age of 16 years in adult clinics is important.

Spectrum of Mutations in Pediatric Non-glomerular Chronic Kidney Disease Stages 2–5

Renal hypodysplasia and cystic kidney diseases, the common non-glomerular causes of pediatric chronic kidney disease (CKD), are usually diagnosed by their clinical and imaging characteristics. The high degree of phenotypic heterogeneity, in both conditions, makes the correct final diagnosis dependent on genetic testing. It is not clear, however, whether the frequencies of damaged alleles vary among different ethnicities in children with non-glomerular CKD, and this will influence the strategy used for genetic testing. In this study, 69 unrelated children (40 boys, 29 girls) of predominantly Han Chinese ethnicity with stage 2–5 non-glomerular CKD caused by suspected renal hypodysplasia or cystic kidney diseases were enrolled and assessed by molecular analysis using proband-only targeted exome sequencing and array-comparative genomic hybridization. Targeted exome sequencing discovered genetic etiologies in 33 patients (47.8%) covering 10 distinct genetic disorders. The clinical diagnoses in 13/48 patients (27.1%) with suspected renal hypodysplasia were confirmed, and two patients were reclassified carrying mutations in nephronophthisis (NPHP) genes. The clinical diagnoses in 16/20 patients (80%) with suspected cystic kidney diseases were confirmed, and one patient was reclassified as carrying a deletion in the hepatocyte nuclear factor-1-beta gene (HNF1B). The diagnosis of one patient with unknown non-glomerular disease was elucidated. No copy number variations were identified in the 20 patients with negative targeted exome sequencing results. NPHP genes were the most common disease-causing genes in the patients with disease onsets above 6 years of age (14/45, 31.1%). The children with stage 2 and 3 CKD at onset were found to carry causative mutations in paired box gene 2 (PAX2) and HNF1B gene (11/24, 45.8%), whereas those with stage 4 and 5 CKD mostly carried causative mutations in NPHP genes (19/45, 42.2%). The causative genes were not suspected by the kidney imaging patterns at disease onset. Thus, our data show that in Chinese children with non-glomerular renal dysfunction caused by renal hypodysplasia and cystic kidney diseases, the common causative genes vary with age and CKD stage at disease onset. These findings have the potential to improve management and genetic counseling of these diseases in clinical practice.

Rare heterozygous GDF6 variants in patients with renal anomalies

Although over 50 genes are known to cause renal malformation if mutated, the underlying genetic basis, most easily identified in syndromic cases, remains unsolved in most patients. In search of novel causative genes, whole-exome sequencing in a patient with renal, i.e., crossed fused renal ectopia, and extrarenal, i.e., skeletal, eye, and ear, malformations yielded a rare heterozygous variant in the GDF6 gene encoding growth differentiation factor 6, a member of the BMP family of ligands. Previously, GDF6 variants were reported to cause pleiotropic defects including skeletal, e.g., vertebral, carpal, tarsal fusions, and ocular, e.g., microphthalmia and coloboma, phenotypes. To assess the role of GDF6 in the pathogenesis of renal malformation, we performed targeted sequencing in 193 further patients identifying rare GDF6 variants in two cases with kidney hypodysplasia and extrarenal manifestations. During development, gdf6 was expressed in the pronephric tubule of Xenopus laevis, and Gdf6 expression was observed in the ureteric tree of the murine kidney by RNA in situ hybridization. CRISPR/Cas9-derived knockout of Gdf6 attenuated migration of murine IMCD3 cells, an effect rescued by expression of wild-type but not mutant GDF6, indicating affected variant function regarding a fundamental developmental process. Knockdown of gdf6 in Xenopus laevis resulted in impaired pronephros development. Altogether, we identified rare heterozygous GDF6 variants in 1.6% of all renal anomaly patients and 5.4% of renal anomaly patients additionally manifesting skeletal, ocular, or auricular abnormalities, adding renal hypodysplasia and fusion to the phenotype spectrum of GDF6 variant carriers and suggesting an involvement of GDF6 in nephrogenesis.

Loss of miR-17~92 results in dysregulation of Cftr in nephron progenitors

We have previously demonstrated that loss of miR-17~92 in nephron progenitors in a mouse model results in renal hypodysplasia and chronic kidney disease. Clinically, decreased congenital nephron endowment because of renal hypodysplasia is associated with an increased risk of hypertension and chronic kidney disease, and this is at least partly dependent on the self-renewal of nephron progenitors. Here, we present evidence for a novel molecular mechanism regulating the self-renewal of nephron progenitors and congenital nephron endowment by the highly conserved miR-17~92 cluster. Whole transcriptome sequencing revealed that nephron progenitors lacking this cluster demonstrated increased Cftr expression. We showed that one member of the cluster, miR-19b, is sufficient to repress Cftr expression in vitro and that perturbation of Cftr activity in nephron progenitors results in impaired proliferation. Together, these data suggest that miR-19b regulates Cftr expression in nephron progenitors, with this interaction playing a role in appropriate nephron progenitor self-renewal during kidney development to generate normal nephron endowment.

Transcription Factor 21 Is Required for Branching Morphogenesis and Regulates the Gdnf-Axis in Kidney Development

BackgroundThe mammalian kidney develops through reciprocal inductive signals between the metanephric mesenchyme and ureteric bud. Transcription factor 21 (Tcf21) is highly expressed in the metanephric mesenchyme, including Six2-expressing cap mesenchyme and Foxd1-expressing stromal mesenchyme. Tcf21 knockout mice die in the perinatal period from severe renal hypodysplasia. In humans, Tcf21 mRNA levels are reduced in renal tissue from human fetuses with renal dysplasia. The molecular mechanisms underlying these renal defects are not yet known.MethodsUsing a variety of techniques to assess kidney development and gene expression, we compared the phenotypes of wild-type mice, mice with germline deletion of the Tcf21 gene, mice with stromal mesenchyme–specific Tcf21 deletion, and mice with cap mesenchyme–specific Tcf21 deletion.ResultsGermline deletion of Tcf21 leads to impaired ureteric bud branching and is accompanied by downregulated expression of Gdnf-Ret-Wnt11, a key pathway required for branching morphogenesis. Selective removal of Tcf21 from the renal stroma is also associated with attenuation of the Gdnf signaling axis and leads to a defect in ureteric bud branching, a paucity of collecting ducts, and a defect in urine concentration capacity. In contrast, deletion of Tcf21 from the cap mesenchyme leads to abnormal glomerulogenesis and massive proteinuria, but no downregulation of Gdnf-Ret-Wnt11 or obvious defect in branching.ConclusionsOur findings indicate that Tcf21 has distinct roles in the cap mesenchyme and stromal mesenchyme compartments during kidney development and suggest that Tcf21 regulates key molecular pathways required for branching morphogenesis.

Prospective Study on Several Urinary Biomarkers as Indicators of Renal Damage in Children with CAKUT

Purpose The aim of the study was to investigate urinary levels of monocyte chemotactic protein-1 (MCP-1), epidermal growth factor (EGF), β-2-microglobulin (β2M), and FAS-ligand (FAS-L) in children with congenital anomalies of kidney and urinary tract (CAKUT) disease at risk of developing glomerular hyperfiltration syndrome. For this reason, we selected patients with multicystic kidney, renal agenesia and renal hypodysplasia, or underwent single nephrectomy. Materials and Methods This prospective, multicentric study was conducted in collaboration between the Pediatric Surgery Unit in Foggia and the Pediatric Nephrology Unit in Bari, Italy. We enrolled 80 children with CAKUT (40 hypodysplasia, 22 agenetic; 10 multicystic; 8 nephrectomy) who underwent extensive urological and nephrological workup. Exclusion criteria were recent urinary tract infections or pyelonephritis, age > 14 years, presence of systemic disease, or hypertension. A single urine sample was collected in a noninvasive way and processed for measuring by enzyme-linked immunosorbent assay urine levels of MCP-1, EGF, β2M, and FAS-L. As control, urine samples were taken from 30 healthy children.Furthermore, we evaluated the urinary ratios uEGF/uMCP-1 (indicator of regenerative vs inflammatory response) and uEGF/uβ2M (indicator of regenerative response vs. tubular damage). Results These results suggest that urinary levels of MCP-1 are overexpressed in CAKUT patients. Furthermore, our findings clearly demonstrated that both uEGF/uMCP-1 and uEGF/uβ2M ratios were significantly downregulated in all patient groups when compared with the control group. Conclusion These findings further support that CAKUT patients may, eventually, experience progressive renal damage and poor regenerative response. The increased urinary levels of MCP-1 in all groups of CAKUT patients suggested that the main factor responsible for the above effects is chronic renal inflammation mediated by local monocytes.