Genetic Contributions to Lower Urinary Tract Dysfunction.

Lower urinary tract dysfunction (LUTD) can manifest as a spectrum of voiding symptoms in childhood, including urinary urgency, frequency, hesitancy, and incontinence. In severe cases, it can lead to frequent urinary tract infections, hydronephrosis, kidney scarring, and chronic kidney disease. Non-neurogenic neurogenic bladder (NNNB) is a diagnosis of exclusion in which children develop discoordination between the detrusor smooth muscle and external urethral sphincter in the absence of neurological or obstructive lesions, resulting in severe LUTD. Historically, such disorders of voiding were thought to result from behavioral maladaptation. However, it is now increasingly recognized that some individuals may have an underlying genetic etiology for their symptoms. Here, we performed exome sequencing for five probands with NNNB or other forms of severe LUTD, and we identified two individuals with monogenic etiologies for their symptoms. One individual had a homozygous exon 9 deletion in HPSE2 and another had a homozygous single amino acid deletion (p.Gly167del) in ARL6. We performed PCR experiments to identify the breakpoints of the HPSE2 exon 9 deletion and implicate microhomology-mediated end joining as a potential mechanism by which the deletion arose. These findings suggest that genetic testing should be considered for children with severe LUTD.

Multisystemic Inflammatory Syndrome in Children (MIS-C) With COVID-19 and Kidney Involvement: Poor Outcomes in a Case Series.

Multisystemic inflammatory syndrome (Mis-C) has emerged in May 2020 as a serious complication of coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV2). A total of 6 children presented to tertiary care hospitals with Mis-C, of which 5 (83%) have died during hospitalization. All included patients presented with respiratory symptoms (ranged from mild to severe acute respiratory distress syndrome) and gastrointestinal symptoms. Most of the patients are known to have medical illnesses. Pediatric Risk of Mortality (PRISM) IV score ranged from 3 to 87. All patients developed acidosis and varying stages of acute kidney injury and electrolyte disturbances. All were treated for coagulopathy, thrombocytopenia, bacterial infections as well as antiviral medications (either ritonavir or lopinavir). Most patients had chest X-ray changes either unilateral or bilateral lung changes. Multisystemic inflammatory syndrome is a rare, yet serious complication of SARS-CoV2 infection in children. Multisystem involvement should be anticipated and promptly treated.

Recessive variants in MYO1C as a potential novel cause of proteinuric kidney disease.

BACKGROUND: Steroid-resistant nephrotic syndrome is the second leading cause of chronic kidney disease among patients < 25 years of age. Through exome sequencing, identification of > 65 monogenic causes has revealed insights into disease mechanisms of nephrotic syndrome (NS). METHODS: To elucidate novel monogenic causes of NS, we combined homozygosity mapping with exome sequencing in a worldwide cohort of 1649 pediatric patients with NS. RESULTS: We identified homozygous missense variants in MYO1C in two unrelated children with NS (c.292C > T, p.R98W; c.2273 A > T, p.K758M). We evaluated publicly available kidney single-cell RNA sequencing datasets and found MYO1C to be predominantly expressed in podocytes. We then performed structural modeling for the identified variants in PyMol using aligned shared regions from two available partial structures of MYO1C (4byf and 4r8g). In both structures, calmodulin, a common regulator of myosin activity, is shown to bind to the IQ motif. At both residue sites (K758; R98), there are ion-ion interactions stabilizing intradomain and ligand interactions: R98 binds to nearby D220 within the myosin motor domain and K758 binds to E14 on a calmodulin molecule. Variants of these charged residues to non-charged amino acids could ablate these ionic interactions, weakening protein structure and function establishing the impact of these variants. CONCLUSION: We here identified recessive variants in MYO1C as a potential novel cause of NS in children.

Prospective Study of Modifiable Risk Factors of Arterial Hypertension and Left Ventricular Hypertrophy in Pediatric Patients on Hemodialysis.

Introduction: Fluid and salt overload in patients on dialysis result in high blood pressure (BP), left ventricular hypertrophy (LVH) and hemodynamic instability, resulting in cardiovascular morbidity. Methods: Analysis of 910 pediatric patients on maintenance hemodialysis/hemodiafiltration (HD/HDF), prospectively followed-up with 2758 observations recorded every 6-months in the International Pediatric Hemodialysis Network (IPHN). Results: Uncontrolled hypertension was present in 55% of observations, with 27% of patients exhibiting persistently elevated predialysis BP. Systolic and diastolic age- and height-standardized BP (BP-SDS) were independently associated with the number of antihypertensive medications (odds ratio [OR] = 1.47, 95% confidence interval 1.39-1.56, 1.36 [1.23-1.36]) and interdialytic weight gain (IDWG; 1.19 [1.14-1.22], 1.09 [1.06-1.11]; all P < 0.0001). IDWG was related to urine output (OR = 0.27 [0.23-0.32]) and dialysate sodium (dNa; 1.06 [1.01-1.10]; all P < 0.0001). The prevalence of masked hypertension was 24%, and HD versus HDF use was an independent risk factor of elevated age- and height-standardized mean arterial pressure (MAP-SDS) (OR = 2.28 [1.18-4.41], P = 0.01). Of the 1135 echocardiograms, 51% demonstrated LVH. Modifiable risk factors included predialysis systolic BP-SDS (OR = 1.06 [1.04-1.09], P < 0.0001), blood hemoglobin (0.97 [0.95-0.99], P = 0.004), HD versus HDF modality (1.09 [1.02-1.18], P = 0.01), and IDWG (1.02 [1.02-1.03], P = 0.04). In addition, HD modality increased the risk of LVH progression (OR = 1.23 [1.03-1.48], P = 0.02). Intradialytic hypotension (IDH) was prevalent in patients progressing to LVH and independently associated with predialysis BP-SDS below 25th percentile, lower number of antihypertensives, HD versus HDF modality, ultrafiltration (UF) rate, and urine output, but not with dNa. Conclusion: Uncontrolled hypertension and LVH are common in pediatric HD, despite intense pharmacologic therapy. The outcome may improve with use of HDF, and superior anemia and IDWG control; the latter via lowering dNa, without increasing the risk of IDH.

Copy number variation analysis in 138 families with steroid-resistant nephrotic syndrome identifies causal homozygous deletions in PLCE1 and NPHS2 in two families.

BACKGROUND: Steroid-resistant nephrotic syndrome (SRNS) is the second most common cause of kidney failure in children and adults under the age of 20 years. Previously, we were able to detect by exome sequencing (ES) a known monogenic cause of SRNS in 25-30% of affected families. However, ES falls short of detecting copy number variants (CNV). Therefore, we hypothesized that causal CNVs could be detected in a large SRNS cohort. METHODS: We performed genome-wide single nucleotide polymorphism (SNP)-based CNV analysis on a cohort of 138 SRNS families, in whom we previously did not identify a genetic cause through ES. We evaluated ES and CNV data for variants in 60 known SRNS genes and in 13 genes in which variants are known to cause a phenocopy of SRNS. We applied previously published, predefined criteria for CNV evaluation. RESULTS: We detected a novel CNV in two genes in 2 out of 138 families (1.5%). The 9,673 bp homozygous deletion in PLCE1 and the 6,790 bp homozygous deletion in NPHS2 were confirmed across the breakpoints by PCR and Sanger sequencing. CONCLUSIONS: We confirmed that CNV analysis can identify the genetic cause in SRNS families that remained unsolved after ES. Though the rate of detected CNVs is minor, CNV analysis can be used when there are no other genetic causes identified. Causative CNVs are less common in SRNS than in other monogenic kidney diseases, such as congenital anomalies of the kidneys and urinary tract, where the detection rate was 5.3%. A higher resolution version of the Graphical abstract is available as Supplementary information.

Insight into prevalence, etiology, and modalities of pediatric chronic dialysis: a comprehensive nationwide analysis.

BACKGROUND: This study aimed to determine the prevalence and etiology of kidney failure (KF) among children below 15 years of age receiving chronic dialysis in Saudi Arabia and describe their dialysis modalities. METHODS: This cross-sectional descriptive study was conducted on 8 August 2022, encompassing all 23 pediatric dialysis centers in Saudi Arabia. Data gathered comprised patient demographics, causes of KF, and the dialysis methods employed. Collected data underwent analysis to determine prevalence of children undergoing chronic dialysis, discern underlying causes of KF, and evaluate distribution of patients across different dialysis modalities. RESULTS: The prevalence of children on chronic dialysis is 77.6 per million children living in Saudi Arabia, equating to 419 children. The predominant underlying cause of KF was congenital anomalies of the kidneys and urinary tract (CAKUT), representing a substantial 41% of cases. Following this, others or unknown etiologies accounted for a noteworthy 25% of cases, with focal segmental glomerulosclerosis (FSGS) comprising 13%, glomerulonephritis at 11%, and congenital nephrotic syndrome contributing 10% to etiological distribution. Regarding dialysis modalities employed, 67% of patients were on peritoneal dialysis (PD), while the remaining 33% were on hemodialysis (HD). CONCLUSIONS: This first nationwide study of pediatric chronic dialysis in Saudi Arabia sheds light on the prevalence of children undergoing chronic dialysis and underlying causes of their KF, thereby contributing to our understanding of clinical management considerations. This research serves as a stepping stone for the development of national registries.

Awareness, Attitudes, and Willingness: A Cross-Sectional Study of Organ Donation in Saudi Arabia.

BACKGROUND: Organ transplantation is inherently dependent on the availability of organ donors. There is a noticeable paucity of literature addressing the rates of organ donation registration and the awareness of Islamic regulations (Fatwa) regarding organ donation within Saudi Arabia. Our study aimed to evaluate the level of organ donation registration, awareness of Islamic regulations, and knowledge of the Saudi Center for Organ Transplantation (SCOT) within the Saudi society. METHODS: We conducted a cross-sectional survey from 30 March to 9 April 2023. This survey aimed to assess the awareness of Islamic (Fatwa) guidance on organ donation, the role of SCOT, and the rate of organ donation registration facilitated through the Tawakkalna app, the official health passport application in Saudi Arabia. RESULTS: Out of 2329 respondents, 21% had registered as potential deceased organ donors, despite 87% acknowledging the importance of organ donation. Awareness of the Islamic Fatwa regarding organ donation was reported by 54.7% of respondents, and 37% recognized the Fatwa's acceptance of brain death criteria. The likelihood of registration as organ donors was higher among Saudi citizens under 45 years of age, females, healthcare workers (HCWs), individuals with higher education, relatives of patients awaiting organ donations, those informed about the Islamic Fatwas, and those willing to donate organs to friends. Conversely, being over the age of 25, Saudi nationality, employment as an HCW, awareness of SCOT, and prior organ donation registration were predictive of a heightened awareness of Islamic Fatwas. However, perceiving the importance of organ donation correlated with a lower awareness of the Fatwas. Significant positive correlations were found between awareness of SCOT, awareness of Fatwas, and registration for organ donation. CONCLUSIONS: While the Saudi population exhibits a high regard for the importance of organ donation, this recognition is not adequately translated into registration rates. The discrepancy may be attributable to limited awareness of SCOT and the relevant Islamic Fatwas. It is imperative to initiate organ donation awareness campaigns that focus on religious authorization to boost organ donation rates and rectify prevalent misconceptions.

Common Risk Variants in AHI1 Are Associated With Childhood Steroid Sensitive Nephrotic Syndrome.

Introduction: Steroid-sensitive nephrotic syndrome (SSNS) is the most common form of kidney disease in children worldwide. Genome-wide association studies (GWAS) have demonstrated the association of SSNS with genetic variation at HLA-DQ/DR and have identified several non-HLA loci that aid in further understanding of disease pathophysiology. We sought to identify additional genetic loci associated with SSNS in children of Sri Lankan and European ancestry. Methods: We conducted a GWAS in a cohort of Sri Lankan individuals comprising 420 pediatric patients with SSNS and 2339 genetic ancestry matched controls obtained from the UK Biobank. We then performed a transethnic meta-analysis with a previously reported European cohort of 422 pediatric patients and 5642 controls. Results: Our GWAS confirmed the previously reported association of SSNS with HLA-DR/DQ (rs9271602, P = 1.12 × 10-27, odds ratio [OR] = 2.75). Transethnic meta-analysis replicated these findings and identified a novel association at AHI1 (rs2746432, P = 2.79 × 10-8, OR = 1.37), which was also replicated in an independent South Asian cohort. AHI1 is implicated in ciliary protein transport and immune dysregulation, with rare variation in this gene contributing to Joubert syndrome type 3. Conclusions: Common variation in AHI1 confers risk of the development of SSNS in both Sri Lankan and European populations. The association with common variation in AHI1 further supports the role of immune dysregulation in the pathogenesis of SSNS and demonstrates that variation across the allele frequency spectrum in a gene can contribute to disparate monogenic and polygenic diseases.

Common Prognostic Biomarkers and Outcomes in Patients with COVID-19 Infection in Saudi Arabia.

Background: COVID-19 is a respiratory disease that eventually became a pandemic, with 300 million people infected around the world. Alongside the improvement in COVID-19 management and vaccine development, identifying biomarkers for COVID-19 has recently been reported to help in early prediction and managing severe cases, which might improve outcomes. Our study aimed to find out if there is any correlation between clinical severity and elevated hematological and biochemical markers in COVID-19 patients and its effect on the outcome. Methods: We have collected retrospective data on socio-demographics, medical history, biomarkers, and disease outcomes from five hospitals and health institutions in the Kingdom of Saudi Arabia. Results: Pneumonia was the most common presentation of COVID-19 in our cohort. The presence of abnormal inflammatory biomarkers (D-dimer, CRP, troponin, LDH, ferritin, and t white blood cells) was significantly associated with unstable COVID-19 disease. In addition, patients with evidence of severe respiratory disease, particularly those who required mechanical ventilation, had higher biomarkers when compared to those with stable respiratory conditions (p < 0.001). Conclusion: Identifying biomarkers predicts outcomes for COVID-19 patients and may significantly help in their management.

Recessive CHRM5 variant as a potential cause of neurogenic bladder.

Neurogenic bladder is caused by disruption of neuronal pathways regulating bladder relaxation and contraction. In severe cases, neurogenic bladder can lead to vesicoureteral reflux, hydroureter, and chronic kidney disease. These complications overlap with manifestations of congenital anomalies of the kidney and urinary tract (CAKUT). To identify novel monogenic causes of neurogenic bladder, we applied exome sequencing (ES) to our cohort of families with CAKUT. By ES, we have identified a homozygous missense variant (p.Gln184Arg) in CHRM5 (cholinergic receptor, muscarinic, 5) in a patient with neurogenic bladder and secondary complications of CAKUT. CHRM5 codes for a seven transmembrane-spanning G-protein-coupled muscarinic acetylcholine receptor. CHRM5 is shown to be expressed in murine and human bladder walls and is reported to cause bladder overactivity in Chrm5 knockout mice. We investigated CHRM5 as a potential novel candidate gene for neurogenic bladder with secondary complications of CAKUT. CHRM5 is similar to the cholinergic bladder neuron receptor CHRNA3, which Mann et al. published as the first monogenic cause of neurogenic bladder. However, functional in vitro studies did not reveal evidence to strengthen the status as a candidate gene. Discovering additional families with CHRM5 variants could help to further assess the genes' candidate status.

Lupus Nephritis in an Adolescent Girl With Hyper-Immunoglobulin E.

We report the case of an adolescent girl with frequent hospital admissions for severe eczematous skin rashes with recurrent epistaxis and chest infections. Investigations revealed persistent severely elevated serum total immunoglobulin E (IgE) levels but normal levels of other immunoglobulins, suggesting hyper-IgE syndrome. The first skin biopsy revealed superficial dermatophytic dermatitis (tinea corpora). Another biopsy performed after six months revealed a prominent basement membrane with dermal mucin, suggesting an underlying autoimmune disease. Her condition was complicated by proteinuria, hematuria, hypertension, and edema. A kidney biopsy revealed class IV lupus nephritis, according to the International Society of Nephrology/Renal Pathology Society (ISN/RPS). Based on the American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) criteria, she was diagnosed with systemic lupus erythematosus (SLE). She was first administered with intravenous pulse methylprednisolone (600 mg/m2) for three consecutive days, followed by oral prednisolone (40 mg/m2) daily, mycophenolate mofetil tablets (600 mg/m2/dose) twice daily, hydroxychloroquine (200 mg) once daily, and three classes of antihypertensive medications. She maintained normal renal functions with no lupus morbidity for 24 months, then rapidly progressed to end-stage kidney disease, and was then started on three to four sessions of regular hemodialysis per week. Hyper-IgE is known to be a marker of immune dysregulation as it facilitates the generation of immune complexes (ICs) that mediate lupus nephritis and juvenile SLE. Regardless of the different factors that are impacting the production of IgE, the present case illustrated that juvenile patients with SLE may have increased IgE levels, indicating that higher IgE levels might have a role in lupus pathogenesis and prognosis. The mechanisms regarding the increased levels of IgE in subjects with lupus need further investigation. Further studies are thus required to assess the incidence, prognosis, and possible new specific management for hyper-IgE in juvenile SLE.

Clinical and molecular characterization of a large primary hyperoxaluria cohort from Saudi Arabia: a retrospective study.

BACKGROUND: Primary hyperoxalurias (PHs) constitute rare disorders resulting in abnormal glyoxalate metabolism. PH-associated phenotypes range from progressive nephrocalcinosis and/or recurrent urolithiasis to early kidney failure. METHODS: A retrospective study was conducted for patients with confirmed PH diagnoses from three tertiary centers in Saudi Arabia. Detailed clinical molecular diagnosis was performed for 25 affected individuals. Whole exome sequencing (WES)-based molecular diagnosis was performed for all affected individuals. RESULTS: The male:female ratio was 52% male (n = 13) and 48% female (n = 12), and consanguinity was present in 88%. Nephrolithiasis and/or nephrocalcinosis were present in all patients. Kidney stones were present in 72%, nephrocalcinosis in 60%, hematuria in 32%, proteinuria in 16%, abdominal pain in 36%, developmental delay in 8%, and chronic kidney disease stage 5 (CKD stage 5) was observed in 28% of the patients. The most common PH disorder was type I caused by variants in the AGXT gene, accounting for 56%. The GRHPR gene variants were identified in 4 patients, 16% of the total cases. Seven patients did not reveal any associated variants. Missense variants were the most commonly observed variants (48%), followed by frame-shift duplication variants (28%). CONCLUSIONS: Characterization of the genetic and clinical aspects of PH in this unique population provides direction for improved patient management and further research. A higher resolution version of the Graphical abstract is available as Supplementary information.

Adapting Clinical Practice Guidelines for Chronic Kidney Disease: Blood Pressure Management and Kidney Replacement Therapy in Adults and Children in the Saudi Arabian Context Using the Grading of Recommendations Assessment, Development, and Evaluation-ADOLOPMENT Methodology.

This practice guideline was developed by the chronic kidney disease (CKD) Task Force, which was composed of clinical and methodological experts. The Saudi Arabian Ministry of Health and its health holding company commissioned this guideline project to support the realization of Vision 2030's health-care transformation pillar. The synthesis of these guidelines was guided by the Grading of Recommendations Assessment, Development, and Evaluation (GRADE)- ADOLOPMENT methodology. The final guidelines addressed 12 clinical questions on the management of blood pressure in patients with CKD through a set of recommen-dations and performance measures. The recom-mendations included antihypertensive agents in children; renin- angiotensin system inhibition (RASi) versus non-RASi in adults; intensive versus standard blood pressure targets; early versus late assessment for kidney replacement therapy (KRT); late versus early preparation strategies for KRT; CKD symptoms during assessment for KRT or conservative manage-ment; initiation of KRT in patients with deteriorating CKD; choice of KRT modality or conservative management in certain CKD patient groups; changing or discontinuing KRT modalities; the frequency of reviews for KRT or conservative management; and information, education, and support. These conditional recommendations were based on a low to very low certainty of evidence, which highlights the need for high-quality randomized trials com-paring different antihypertensive agents in patients with CKD.

A Multicenter Study Evaluating the Discontinuation of Eculizumab Therapy in Children with Atypical Hemolytic Uremic Syndrome.

BACKGROUND: Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy (TMA), which has been treated successfully with eculizumab. The optimal duration of eculizumab in treating patients with aHUS remains poorly defined. METHODS: We conducted a multicenter retrospective study in the Arabian Gulf region for children of less than 18 years of age who were diagnosed with aHUS and who discontinued eculizumab between June 2013 and June 2021 to assess the rate and risk factors of aHUS recurrence. RESULTS: We analyzed 28 patients with a clinical diagnosis of aHUS who had discontinued eculizumab. The most common reason for the discontinuation of eculizumab was renal and hematological remission (71.4%), followed by negative genetic testing (28.6%). During a median follow-up period of 24 months after discontinuation, 8 patients (28.5%) experienced HUS relapse. The risk factors of recurrence were positive genetic mutations (p = 0.020). On the other hand, there was no significant relationship between the relapse and age of presentation, the need for acute dialysis, the duration of eculizumab therapy before discontinuation, or the timing of eculizumab after the presentation. Regarding the renal outcomes after discontinuation, 23 patients were in remission with normal renal function, while 4 patients had chronic kidney disease (CKD) (three of them had pre-existing chronic kidney disease (CKD) before discontinuation, and one case developed a new CKD after discontinuation) and one patient underwent transplantation. CONCLUSIONS: The discontinuation of eculizumab in patients with aHUS is not without risk; it can result in HUS recurrence. Eculizumab discontinuation can be performed with close monitoring of the patients. It is essential to assess risk the factors for relapse before eculizumab discontinuation, in particular in children with a positive complement variant and any degree of residual CKD, as HUS relapse may lead to additional loss of kidney function. Resuming eculizumab promptly after relapse is effective in most patients.

Copy Number Variation Analysis Facilitates Identification of Genetic Causation in Patients with Congenital Anomalies of the Kidney and Urinary Tract.

Background: Congenital anomalies of the kidneys and urinary tract (CAKUT) are the most common cause of chronic kidney disease among children and adults younger than 30 yr. In our previous study, whole-exome sequencing (WES) identified a known monogenic cause of isolated or syndromic CAKUT in 13% of families with CAKUT. However, WES has limitations and detection of copy number variations (CNV) is technically challenging, and CNVs causative of CAKUT have previously been detected in up to 16% of cases. Objective: To detect CNVs causing CAKUT in this WES cohort and increase the diagnostic yield. Design setting and participants: We performed a genome-wide single nucleotide polymorphism (SNP)-based CNV analysis on the same CAKUT cohort for whom WES was previously conducted. Outcome measurements and statistical analysis: We evaluated and classified the CNVs using previously published predefined criteria. Results and limitations: In a cohort of 170 CAKUT families, we detected a pathogenic CNV known to cause CAKUT in nine families (5.29%, 9/170). There were no competing variants on genome-wide CNV analysis or WES analysis. In addition, we identified novel likely pathogenic CNVs that may cause a CAKUT phenotype in three of the 170 families (1.76%). Conclusions: CNV analysis in this cohort of 170 CAKUT families previously examined via WES increased the rate of diagnosis of genetic causes of CAKUT from 13% on WES to 18% on WES + CNV analysis combined. We also identified three candidate loci that may potentially cause CAKUT. Patient summary: We conducted a genetics study on families with congenital anomalies of the kidney and urinary tract (CAKUT). We identified gene mutations that can explain CAKUT symptoms in 5.29% of the families, which increased the percentage of genetic causes of CAKUT to 18% from a previous study, so roughly one in five of our patients with CAKUT had a genetic cause. These analyses can help patients with CAKUT and their families in identifying a possible genetic cause.

Parathyroid hormone and phosphate homeostasis in patients with Bartter and Gitelman syndrome: an international cross-sectional study.

BACKGROUND: Small cohort studies have reported high parathyroid hormone (PTH) levels in patients with Bartter syndrome and lower serum phosphate levels have anecdotally been reported in patients with Gitelman syndrome. In this cross-sectional study, we assessed PTH and phosphate homeostasis in a large cohort of patients with salt-losing tubulopathies. METHODS: Clinical and laboratory data of 589 patients with Bartter and Gitelman syndrome were provided by members of the European Rare Kidney Diseases Reference Network (ERKNet) and the European Society for Paediatric Nephrology (ESPN). RESULTS: A total of 285 patients with Bartter syndrome and 304 patients with Gitelman syndrome were included for analysis. Patients with Bartter syndrome type I and II had the highest median PTH level (7.5 pmol/L) and 56% had hyperparathyroidism (PTH >7.0 pmol/L). Serum calcium was slightly lower in Bartter syndrome type I and II patients with hyperparathyroidism (2.42 versus 2.49 mmol/L; P = .038) compared to those with normal PTH levels and correlated inversely with PTH (rs -0.253; P = .009). Serum phosphate and urinary phosphate excretion did not correlate with PTH. Overall, 22% of patients had low serum phosphate levels (phosphate-standard deviation score < -2), with the highest prevalence in patients with Bartter syndrome type III (32%). Serum phosphate correlated with tubular maximum reabsorption of phosphate/glomerular filtration rate (TmP/GFR) (rs 0.699; P < .001), suggesting renal phosphate wasting. CONCLUSIONS: Hyperparathyroidism is frequent in patients with Bartter syndrome type I and II. Low serum phosphate is observed in a significant number of patients with Bartter and Gitelman syndrome and appears associated with renal phosphate wasting.

Whole exome sequencing identifies potential candidate genes for spina bifida derived from mouse models.

Spina bifida (SB) is the second most common nonlethal congenital malformation. The existence of monogenic SB mouse models and human monogenic syndromes with SB features indicate that human SB may be caused by monogenic genes. We hypothesized that whole exome sequencing (WES) allows identification of potential candidate genes by (i) generating a list of 136 candidate genes for SB, and (ii) by unbiased exome-wide analysis. We generated a list of 136 potential candidate genes from three categories and evaluated WES data of 50 unrelated SB cases for likely deleterious variants in 136 potential candidate genes, and for potential SB candidate genes exome-wide. We identified 6 likely deleterious variants in 6 of the 136 potential SB candidate genes in 6 of the 50 SB cases, whereof 4 genes were derived from mouse models, 1 gene was derived from human nonsyndromic SB, and 1 gene was derived from candidate genes known to cause human syndromic SB. In addition, by unbiased exome-wide analysis, we identified 12 genes as potential candidates for SB. Identification of these 18 potential candidate genes in larger SB cohorts will help decide which ones can be considered as novel monogenic causes of human SB.

Childhood nephrolithiasis and nephrocalcinosis caused by metabolic diseases and renal tubulopathy: A retrospective study from 2 tertiary centers.

OBJECTIVES: To study childhood nephrolithiasis and nephrocalcinosis caused by metabolic disorders, distal renal tubular acidosis (dRTA), and familial hypomagnesemia, hypercalciuria, and nephrocalcinosis (FHHNC). METHODS: We retrospectively evaluated 86 children presented over 10 years (2011-2021), with nephrolithiasis (89%) and nephrocalcinosis (11%) caused by metabolic disorders (62%), FHHNC (21%), and dRTA (17%). RESULTS: The mean age at discovery was 72.7 months. The underlying metabolic etiologies included hyperoxaluria (38%), cystinuria (32%), hypercalciuria (24%), and hyperuricosuria (6%). Genetic testing was carried out for 23 patients. Hyperoxaluria was typically treated medically (75%). However, the majority progressed to end-stage kidney disease (ESKD). Most children with cystinuria, hypercalciuria, and hyperuricosuria required medical and surgical intervention. Patients with FHHNC typically presented with nephrocalcinosis. Genetic testing revealed Claudin-16 mutations in 7 children. Patients often progressed to stage II-IV chronic kidney disease (61%) and ESKD (6%). Patients with dRTA typically presented with nephrocalcinosis (80%), as well as poor weight gain and failure to thrive (86%), and medical treatment included sodium bicarbonate and potassium replacement. Despite nephrocalcinosis progression, most patients had normal renal function (53%), although the remaining 47% progressed to chronic kidney disease (none reached ESKD). CONCLUSION: Childhood nephrolithiasis is mainly related to metabolic disorders and is associated with poor renal outcomes. Nephrocalcinosis and nephrolithiasis have poor outcomes when associated with FHHNC, while nephrocalcinosis associated with dRTA has relatively good renal outcomes.

Steroid-sensitive nephrotic syndrome candidate gene CLVS1 regulates podocyte oxidative stress and endocytosis.

We performed next-generation sequencing in patients with familial steroid-sensitive nephrotic syndrome (SSNS) and identified a homozygous segregating variant (p.H310Y) in the gene encoding clavesin-1 (CLVS1) in a consanguineous family with 3 affected individuals. Knockdown of the clavesin gene in zebrafish (clvs2) produced edema phenotypes due to disruption of podocyte structure and loss of glomerular filtration barrier integrity that could be rescued by WT CLVS1 but not the p.H310Y variant. Analysis of cultured human podocytes with CRISPR/Cas9-mediated CLVS1 knockout or homozygous H310Y knockin revealed deficits in clathrin-mediated endocytosis and increased susceptibility to apoptosis that could be rescued with corticosteroid treatment, mimicking the steroid responsiveness observed in patients with SSNS. The p.H310Y variant also disrupted binding of clavesin-1 to α-tocopherol transfer protein, resulting in increased reactive oxygen species (ROS) accumulation in CLVS1-deficient podocytes. Treatment of CLVS1-knockout or homozygous H310Y-knockin podocytes with pharmacological ROS inhibitors restored viability to control levels. Taken together, these data identify CLVS1 as a candidate gene for SSNS, provide insight into therapeutic effects of corticosteroids on podocyte cellular dynamics, and add to the growing evidence of the importance of endocytosis and oxidative stress regulation to podocyte function.