Diagnosis and management of primary hyperoxalurias: best practices.

The primary hyperoxalurias (PH 1, 2, and 3) are rare autosomal recessive disorders of glyoxylate metabolism resulting in hepatic overproduction of oxalate. Clinical presentations that should prompt consideration of PH include kidney stones, nephrocalcinosis, and kidney failure of unknown etiology, especially with echogenic kidneys on ultrasound. PH1 is the most common and severe of the primary hyperoxalurias with a high incidence of kidney failure as early as infancy. Until the recent availability of a novel RNA interference (RNAi) agent, PH care was largely supportive of eventual need for kidney/liver transplantation in PH1 and PH2. Together with the Oxalosis and Hyperoxaluria Foundation, the authors developed a diagnostic algorithm for PH1 and in this report outline best clinical practices related to its early diagnosis, supportive treatment, and long-term management, including the use of the novel RNAi. PH1-focused approaches to dialysis and kidney/liver transplantation for PH patients with progression to chronic kidney disease/kidney failure and systemic oxalosis are suggested. Therapeutic advances for this devastating disease heighten the importance of early diagnosis and informed treatment.

PHYOX2: a pivotal randomized study of nedosiran in primary hyperoxaluria type 1 or 2.

Nedosiran is an investigational RNA interference agent designed to inhibit expression of hepatic lactate dehydrogenase, the enzyme thought responsible for the terminal step of oxalate synthesis. Oxalate overproduction is the hallmark of all genetic subtypes of primary hyperoxaluria (PH). In this double-blind, placebo-controlled study, we randomly assigned (2:1) 35 participants with PH1 (n = 29) or PH2 (n = 6) with eGFR ≥30 mL/min/1.73 m2 to subcutaneous nedosiran or placebo once monthly for 6 months. The area under the curve (AUC) of percent reduction from baseline in 24-hour urinary oxalate (Uox) excretion (primary endpoint), between day 90-180, was significantly greater with nedosiran vs placebo (least squares mean [SE], +3507 [788] vs -1664 [1190], respectively; difference, 5172; 95% CI 2929-7414; P < 0.001). A greater proportion of participants receiving nedosiran vs placebo achieved normal or near-normal (<0.60 mmol/24 hours; <1.3 × ULN) Uox excretion on ≥2 consecutive visits starting at day 90 (50% vs 0; P = 0.002); this effect was mirrored in the nedosiran-treated PH1 subgroup (64.7% vs 0; P < 0.001). The PH1 subgroup maintained a sustained Uox reduction while on nedosiran, whereas no consistent effect was seen in the PH2 subgroup. Nedosiran-treated participants with PH1 also showed a significant reduction in plasma oxalate versus placebo (P = 0.017). Nedosiran was generally safe and well tolerated. In the nedosiran arm, the incidence of injection-site reactions was 9% (all mild and self-limiting). In conclusion, participants with PH1 receiving nedosiran had clinically meaningful reductions in Uox, the mediator of kidney damage in PH.

Mutations of the Transcriptional Corepressor ZMYM2 Cause Syndromic Urinary Tract Malformations.

Congenital anomalies of the kidney and urinary tract (CAKUT) constitute one of the most frequent birth defects and represent the most common cause of chronic kidney disease in the first three decades of life. Despite the discovery of dozens of monogenic causes of CAKUT, most pathogenic pathways remain elusive. We performed whole-exome sequencing (WES) in 551 individuals with CAKUT and identified a heterozygous de novo stop-gain variant in ZMYM2 in two different families with CAKUT. Through collaboration, we identified in total 14 different heterozygous loss-of-function mutations in ZMYM2 in 15 unrelated families. Most mutations occurred de novo, indicating possible interference with reproductive function. Human disease features are replicated in X. tropicalis larvae with morpholino knockdowns, in which expression of truncated ZMYM2 proteins, based on individual mutations, failed to rescue renal and craniofacial defects. Moreover, heterozygous Zmym2-deficient mice recapitulated features of CAKUT with high penetrance. The ZMYM2 protein is a component of a transcriptional corepressor complex recently linked to the silencing of developmentally regulated endogenous retrovirus elements. Using protein-protein interaction assays, we show that ZMYM2 interacts with additional epigenetic silencing complexes, as well as confirming that it binds to FOXP1, a transcription factor that has also been linked to CAKUT. In summary, our findings establish that loss-of-function mutations of ZMYM2, and potentially that of other proteins in its interactome, as causes of human CAKUT, offering new routes for studying the pathogenesis of the disorder.

OXGR1 is a candidate disease gene for human calcium oxalate nephrolithiasis.

PURPOSE: Nephrolithiasis (NL) affects 1 in 11 individuals worldwide, leading to significant patient morbidity. NL is associated with nephrocalcinosis (NC), a risk factor for chronic kidney disease. Causative genetic variants are detected in 11% to 28% of NL and/or NC, suggesting that additional NL/NC-associated genetic loci await discovery. Therefore, we employed genomic approaches to discover novel genetic forms of NL/NC. METHODS: Exome sequencing and directed sequencing of the OXGR1 locus were performed in a worldwide NL/NC cohort. Putatively deleterious, rare OXGR1 variants were functionally characterized. RESULTS: Exome sequencing revealed a heterozygous OXGR1 missense variant (c.371T>G, p.L124R) cosegregating with calcium oxalate NL and/or NC disease in an autosomal dominant inheritance pattern within a multigenerational family with 5 affected individuals. OXGR1 encodes 2-oxoglutarate (α-ketoglutarate [AKG]) receptor 1 in the distal nephron. In response to its ligand AKG, OXGR1 stimulates the chloride-bicarbonate exchanger, pendrin, which also regulates transepithelial calcium transport in cortical connecting tubules. Strong amino acid conservation in orthologs and paralogs, severe in silico prediction scores, and extreme rarity in exome population databases suggested that the variant was deleterious. Interrogation of the OXGR1 locus in 1107 additional NL/NC families identified 5 additional deleterious dominant variants in 5 families with calcium oxalate NL/NC. Rare, potentially deleterious OXGR1 variants were enriched in patients with NL/NC compared with Exome Aggregation Consortium controls (χ2 = 7.117, P = .0076). Wild-type OXGR1-expressing Xenopus oocytes exhibited AKG-responsive Ca2+ uptake. Of 5 NL/NC-associated missense variants, 5 revealed impaired AKG-dependent Ca2+ uptake, demonstrating loss of function. CONCLUSION: Rare, dominant loss-of-function OXGR1 variants are associated with recurrent calcium oxalate NL/NC disease.

Nuestra Recuperación [Our Recovery]: using photovoice to understand the factors that influence recovery in Latinx populations.

BACKGROUND: Photovoice is a form of visual ethnography intended to engage impacted communities in research followed by action to ameliorate the injustices under study. Photovoice has increased in use, especially in collaboration with Latinx communities addressing health inequities. The Latinx population comprises nearly 18% of the overall United States population and according to the census is projected to reach just under 30% by 2060. This diverse panethnic community faces significant structural barriers in accessing services. Racism and the resulting marginalization, specifically, contributes to limited access to recovery services and treatment. Making meaningful advances in substance use disorder training, intervention and policy necessitates learning alongside the Latinx community. METHODS: We partnered with a Latinx serving integrated behavioral health and primary care setting in Boston Massachusetts to explore barriers and facilitators to recovery using photovoice. Spanish-speaking Latinx adults with a substance use disorder participated. The group met for three photovoice sessions over a six-week period. Together group members critically analyzed photographs using the SHOWeD method. RESULTS: Findings indicate a sense of purpose and meaning, security, faith and housing are important elements of recovery. The results illustrated the importance of sources of connection in maintaining sobriety. Through this photovoice project, Latinx Spanish speaking participants highlighted barriers and facilitators to their substance use disorder recovery which spanned individual, community, and structural levels. CONCLUSIONS: The experiences and voices of the Latinx community are crucial to drive discussions that advance policy (e.g., housing stability and access), enhance providers' understanding of Latinx Spanish-speakers' substance use disorder recovery, and inform culturally and linguistically appropriate services. This study demonstrated that photovoice is highly acceptable and feasible among Latinx clients receiving substance use disorder services. Visual images related to housing, faith, etc. communicate challenges, power structures, as well as hopes to policymakers at multiple levels (e.g., institution/ agency, state).

Safety, pharmacodynamics, and exposure-response modeling results from a first-in-human phase 1 study of nedosiran (PHYOX1) in primary hyperoxaluria.

Primary hyperoxaluria (PH) is a family of ultra-rare autosomal recessive inherited disorders of hepatic glyoxylate metabolism characterized by oxalate overproduction. Nedosiran is an RNA interference agent that inhibits hepatic lactate dehydrogenase, the enzyme responsible for the common, final step of oxalate production in all three genetic subtypes of PH. Here, we assessed in a two-part, randomized, single-ascending-dose, phase 1 study (PHYOX1) the safety, pharmacokinetics, pharmacodynamics, and exposure-response of subcutaneous nedosiran in 25 healthy participants (Group A) and 18 patients with PH1 or PH2 (Group B). Group A received nedosiran (0.3, 1.5, 3.0, 6.0, then 12.0 mg/kg) or placebo, and Group B received open-label nedosiran (1.5, 3.0, or 6.0 mg/kg). No significant safety concerns were identified. Injection site reactions (four or more hours post dose) occurred in 13.3% of participants in Group A and 27.8% of participants in Group B. Mean maximum reduction in 24-hour urinary oxalate excretion from baseline to day 57 (end of study) across Group B dose cohorts was 55% (range: 22%-100%) after single-dose nedosiran, with 33% participants reaching normal 24-hour urinary oxalate excretion. Based on the available modeling and simulation data, a fixed monthly dose of nedosiran 160 mg (free acid; equivalent to 170 mg sodium salt) in adults was associated with the highest proportion of simulated individuals achieving normal or near-normal 24-hour urinary oxalate excretion and fewest fluctuations in urinary oxalate response. Thus, single-dose nedosiran demonstrated acceptable safety and evidence of a pharmacodynamic effect in both PH1 and PH2 subpopulations consistent with its mechanism of action.

Reverse phenotyping facilitates disease allele calling in exome sequencing of patients with CAKUT.

PURPOSE: Congenital anomalies of the kidneys and urinary tract (CAKUT) constitute the leading cause of chronic kidney disease in children. In total, 174 monogenic causes of isolated or syndromic CAKUT are known. However, syndromic features may be overlooked when the initial clinical diagnosis of CAKUT is made. We hypothesized that the yield of a molecular genetic diagnosis by exome sequencing (ES) can be increased by applying reverse phenotyping, by re-examining the case for signs/symptoms of the suspected clinical syndrome that results from the genetic variant detected by ES. METHODS: We conducted ES in an international cohort of 731 unrelated families with CAKUT. We evaluated ES data for variants in 174 genes, in which variants are known to cause isolated or syndromic CAKUT. In cases in which ES suggested a previously unreported syndromic phenotype, we conducted reverse phenotyping. RESULTS: In 83 of 731 (11.4%) families, we detected a likely CAKUT-causing genetic variant consistent with an isolated or syndromic CAKUT phenotype. In 19 of these 83 families (22.9%), reverse phenotyping yielded syndromic clinical findings, thereby strengthening the genotype-phenotype correlation. CONCLUSION: We conclude that employing reverse phenotyping in the evaluation of syndromic CAKUT genes by ES provides an important tool to facilitate molecular genetic diagnostics in CAKUT.

Dietary Risk Factors for Pediatric Kidney Stones: A Case-Control Study.

PURPOSE: Data are scarce regarding dietary risk factors for pediatric nephrolithiasis. Our objective was to perform a case-control study (nonmatched) of the association of dietary nutrients with pediatric urolithiasis. MATERIALS AND METHODS: We obtained dietary information from pediatric urolithiasis patients (from stone clinic in 2013-2016) and healthy controls (well-child visit at primary care in 2011-2012). Survey results were converted to standard nutrient intakes. Children younger than 5 years of age and those with extreme calorie intake values (<500 or >5,000 kcal/day) were excluded. The association of individual nutrients with urolithiasis was assessed by bivariate analysis results and machine-learning methods. A multivariable logistic regression model was fitted using urolithiasis as the outcome. RESULTS: We included 285 patients (57 stones/228 controls). Mean±SD age was 8.9±3.6 years (range 5-20). Of the patients 47% were male. After adjusting for age, sex, body mass index (obese/overweight/normal), calorie intake and oxalate, urolithiasis was associated with higher dietary sodium (OR=2.43 [95% CI=1.40-4.84] per quintile increase, p=0.004), calcium (OR=1.73 [95% CI=1.07-3.00] per quintile increase, p=0.034) and beta carotene (OR=2.01 [95% CI=1.06-4.18] per quintile increase, p=0.042), and lower potassium (OR=0.31 [95% CI=0.13-0.63] per quintile increase, p=0.003). Sensitivity analysis was performed by removing oxalate from the model and limiting the sample to patients aged 5-13 years, with similar results. CONCLUSIONS: In our cohort, higher dietary intake of calcium, sodium and beta carotene, and lower potassium intake were associated with pediatric urolithiasis. This is the first study using a detailed dietary survey to identify dietary risk factors for pediatric urolithiasis. Further research is warranted to delineate the mechanisms and to generate a lower risk diet profile for pediatric urolithiasis.

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.

Incidence of Urinary Tract Infections in Newborns with Spina Bifida-Is Antibiotic Prophylaxis Necessary?

PURPOSE: Urinary tract infections commonly occur in patients with spina bifida and pose a risk of renal scarring. Routine antibiotic prophylaxis has been utilized in newborns with spina bifida to prevent urinary tract infections. We hypothesized that prophylaxis can safely be withheld in newborns with spina bifida until clinical assessment allows for risk stratification. MATERIALS AND METHODS: Newborns with myelomeningocele at 9 institutions were prospectively enrolled in the UMPIRE study and managed by a standardized protocol with a strict definition of urinary tract infection. Patient data were collected regarding details of reported urinary tract infection, baseline renal ultrasound findings, vesicoureteral reflux, use of clean intermittent catheterization and circumcision status in boys. Risk ratios and corresponding 95% confidence intervals were calculated using log-binomial models. RESULTS: From February 2015 through August 2019 data were available on 299 newborns (50.5% male). During the first 4 months of life, 48 newborns (16.1%) were treated for urinary tract infection with 23 (7.7%) having positive cultures; however, only 12 (4.0%) met the strict definition of urinary tract infection. Infants with grade 3-4 hydronephrosis had an increased risk of urinary tract infection compared to infants with no hydronephrosis (RR=10.1; 95% CI=2.8, 36.3). Infants on clean intermittent catheterization also had an increased risk of urinary tract infection (RR=3.3; 95% CI=1.0, 10.5). CONCLUSIONS: The incidence of a culture positive, symptomatic urinary tract infection among newborns with spina bifida in the first 4 months of life was low. Patients with high grades of hydronephrosis or those on clean intermittent catheterization had a significantly greater incidence of urinary tract infection. Our findings suggest that routine antibiotic prophylaxis may not be necessary for most newborns with spina bifida.

Chronic kidney disease and upper tract concerns after congenital and acquired urinary tract abnormalities: considerations for transition of care in teens and young adults.

PURPOSE: To emphasize the burden that chronic kidney disease (CKD) and its complications place on overall health and well-being over the lifetime in individuals with congenital and acquired urinary tract abnormalities. METHODS: Topic-based literature review was performed and professional opinion was obtained to describe the scope of medical challenges faced by both teens and adults and their health care providers in the context of congenital and acquired urinary tract abnormalities. RESULTS: Challenges include accurate assessment of glomerular filtration rate; engaging for consistent surveillance of blood pressure, proteinuria, and medical complications of CKD that increase the risk of progression to end-stage renal disease and affect general health; achieving early referral to nephrology for better outcomes; managing renal complications within the unique limitations of lower urinary tract function; treating upper tract urolithiasis in the atypical urinary tract; and preparing for successful renal transplant. CONCLUSION: In individuals with congenital or acquired abnormalities of the urinary tract, there is an inherent risk of CKD with its associated morbidity and increased mortality risk. Interplay between the upper and lower urinary tract impacts CKD progression. Collaborative management between urology and nephrology is highly recommended to address the unique challenges for each individual over the lifetime.

Whole exome sequencing identified ATP6V1C2 as a novel candidate gene for recessive distal renal tubular acidosis.

Distal renal tubular acidosis is a rare renal tubular disorder characterized by hyperchloremic metabolic acidosis and impaired urinary acidification. Mutations in three genes (ATP6V0A4, ATP6V1B1 and SLC4A1) constitute a monogenic causation in 58-70% of familial cases of distal renal tubular acidosis. Recently, mutations in FOXI1 have been identified as an additional cause. Therefore, we hypothesized that further monogenic causes of distal renal tubular acidosis remain to be discovered. Panel sequencing and/or whole exome sequencing was performed in a cohort of 17 families with 19 affected individuals with pediatric onset distal renal tubular acidosis. A causative mutation was detected in one of the three "classical" known distal renal tubular acidosis genes in 10 of 17 families. The seven unsolved families were then subjected to candidate whole exome sequencing analysis. Potential disease causing mutations in three genes were detected: ATP6V1C2, which encodes another kidney specific subunit of the V-type proton ATPase (1 family); WDR72 (2 families), previously implicated in V-ATPase trafficking in cells; and SLC4A2 (1 family), a paralog of the known distal renal tubular acidosis gene SLC4A1. Two of these mutations were assessed for deleteriousness through functional studies. Yeast growth assays for ATP6V1C2 revealed loss-of-function for the patient mutation, strongly supporting ATP6V1C2 as a novel distal renal tubular acidosis gene. Thus, we provided a molecular diagnosis in a known distal renal tubular acidosis gene in 10 of 17 families (59%) with this disease, identified mutations in ATP6V1C2 as a novel human candidate gene, and provided further evidence for phenotypic expansion in WDR72 mutations from amelogenesis imperfecta to distal renal tubular acidosis.

Kidney Function Surveillance in the National Spina Bifida Patient Registry: A Retrospective Cohort Study.

PURPOSE: Chronic kidney disease affects 25% to 50% of patients with spina bifida. Guidelines recommend kidney function surveillance in these patients but practice patterns are unknown. Variations in kidney function surveillance were assessed in patients with spina bifida based on the hypothesis that the treating clinic and spina bifida type would be associated with kidney function surveillance. MATERIALS AND METHODS: A retrospective cohort study was conducted of U.S. patients in the National Spina Bifida Patient Registry from 2013 to 2018. Followup was anchored at the 2013 visit. Participants with either an outcome event within 2 years of followup or more than 2 years of followup without an outcome event were included. Primary outcome was kidney function surveillance, defined as at least 1 renal ultrasound and serum creatinine within 2 years of followup. Primary exposures were clinic and spina bifida type, which were analyzed with covariates including sociodemographic and clinical characteristics in logistic regression models for their association with the outcome. Sensitivity analyses were performed using different kidney function surveillance definitions. RESULTS: Of 8,351 patients 5,445 were included with a median followup of 3.0 years. Across 23 treating clinics kidney function surveillance rates averaged 62% (range 6% to 100%). In multivariable models kidney function surveillance was associated with treating clinic, younger patient age, functional lesion level, nonambulatory status and prior bladder augmentation. Treating clinic remained a significant predictor of kidney function surveillance in all sensitivity analyses. CONCLUSIONS: Within the National Spina Bifida Patient Registry wide variation exists in practice of kidney function surveillance across treating clinics despite adjustment for key patient characteristics.

Whole-Exome Sequencing Enables a Precision Medicine Approach for Kidney Transplant Recipients.

BACKGROUND: Whole-exome sequencing (WES) finds a CKD-related mutation in approximately 20% of patients presenting with CKD before 25 years of age. Although provision of a molecular diagnosis could have important implications for clinical management, evidence is lacking on the diagnostic yield and clinical utility of WES for pediatric renal transplant recipients. METHODS: To determine the diagnostic yield of WES in pediatric kidney transplant recipients, we recruited 104 patients who had received a transplant at Boston Children's Hospital from 2007 through 2017, performed WES, and analyzed results for likely deleterious variants in approximately 400 genes known to cause CKD. RESULTS: By WES, we identified a genetic cause of CKD in 34 out of 104 (32.7%) transplant recipients. The likelihood of detecting a molecular genetic diagnosis was highest for patients with urinary stone disease (three out of three individuals), followed by renal cystic ciliopathies (seven out of nine individuals), steroid-resistant nephrotic syndrome (nine out of 21 individuals), congenital anomalies of the kidney and urinary tract (ten out of 55 individuals), and chronic glomerulonephritis (one out of seven individuals). WES also yielded a molecular diagnosis for four out of nine individuals with ESRD of unknown etiology. The WES-related molecular genetic diagnosis had implications for clinical care for five patients. CONCLUSIONS: Nearly one third of pediatric renal transplant recipients had a genetic cause of their kidney disease identified by WES. Knowledge of this genetic information can help guide management of both transplant patients and potential living related donors.

Mutations in SLC26A1 Cause Nephrolithiasis.

Nephrolithiasis, a condition in which urinary supersaturation leads to stone formation in the urinary system, affects about 5%-10% of individuals worldwide at some point in their lifetime and results in significant medical costs and morbidity. To date, mutations in more than 30 genes have been described as being associated with nephrolithiasis, and these mutations explain about 15% of kidney stone cases, suggesting that additional nephrolithiasis-associated genes remain to be discovered. To identify additional genes whose mutations are linked to nephrolithiasis, we performed targeted next-generation sequencing of 18 hypothesized candidate genes in 348 unrelated individuals with kidney stones. We detected biallelic mutations in SLC26A1 (solute carrier family 26 member 1) in two unrelated individuals with calcium oxalate kidney stones. We show by immunofluorescence, immunoblotting, and glycosylation analysis that the variant protein mimicking p.Thr185Met has defects in protein folding or trafficking. In addition, by measuring anion exchange activity of SLC26A1, we demonstrate that all the identified mutations in SLC26A1 result in decreased transporter activity. Our data identify SLC26A1 mutations as causing a recessive Mendelian form of nephrolithiasis.

Baseline Urinary Tract Imaging in Infants Enrolled in the UMPIRE Protocol for Children with Spina Bifida.

PURPOSE: The lifetime risk of renal damage in children with spina bifida is high but only limited baseline imaging data are available for this population. We evaluated a large prospective cohort of infants with spina bifida to define their baseline imaging characteristics. MATERIALS AND METHODS: The UMPIRE Protocol for Young Children with Spina Bifida is an iterative quality improvement protocol that follows a cohort of newborns at 9 United States centers. Using descriptive statistics, we report the initial baseline imaging characteristics, specifically regarding renal bladder ultrasound, cystogram and dimercaptosuccinic acid nuclear medicine scan. RESULTS: Data on 193 infants from 2015 to 2018 were analyzed. Renal-bladder ultrasound was normal in 55.9% of infants, while 40.4% had Society for Fetal Urology grade 1 to 2 hydronephrosis in at least 1 kidney, 3.7% had grade 3 to 4 hydronephrosis in either kidney and 21.8% had grade 1 or higher bilateral hydronephrosis. There was no vesicoureteral reflux in 84.6% of infants. A third of enrolled infants underwent dimercaptosuccinic acid nuclear medicine renal scan, of whom 92.4% had no renal defects and 93.9% had a difference in differential function of less than 15%. CONCLUSIONS: The majority of infants born with spina bifida have normal baseline imaging characteristics and normal urinary tract anatomy at birth. This proactive protocol offers careful scheduled surveillance of the urinary tract with the goal of lifelong maintenance of normal renal function and healthy genitourinary development.

Whole-Exome Sequencing Identifies Causative Mutations in Families with Congenital Anomalies of the Kidney and Urinary Tract.

BACKGROUND: Congenital anomalies of the kidney and urinary tract (CAKUT) are the most prevalent cause of kidney disease in the first three decades of life. Previous gene panel studies showed monogenic causation in up to 12% of patients with CAKUT. METHODS: We applied whole-exome sequencing to analyze the genotypes of individuals from 232 families with CAKUT, evaluating for mutations in single genes known to cause human CAKUT and genes known to cause CAKUT in mice. In consanguineous or multiplex families, we additionally performed a search for novel monogenic causes of CAKUT. RESULTS: In 29 families (13%), we detected a causative mutation in a known gene for isolated or syndromic CAKUT that sufficiently explained the patient's CAKUT phenotype. In three families (1%), we detected a mutation in a gene reported to cause a phenocopy of CAKUT. In 15 of 155 families with isolated CAKUT, we detected deleterious mutations in syndromic CAKUT genes. Our additional search for novel monogenic causes of CAKUT in consanguineous and multiplex families revealed a potential single, novel monogenic CAKUT gene in 19 of 232 families (8%). CONCLUSIONS: We identified monogenic mutations in a known human CAKUT gene or CAKUT phenocopy gene as the cause of disease in 14% of the CAKUT families in this study. Whole-exome sequencing provides an etiologic diagnosis in a high fraction of patients with CAKUT and will provide a new basis for the mechanistic understanding of CAKUT.

Whole exome sequencing frequently detects a monogenic cause in early onset nephrolithiasis and nephrocalcinosis.

The incidence of nephrolithiasis continues to rise. Previously, we showed that a monogenic cause could be detected in 11.4% of individuals with adult-onset nephrolithiasis or nephrocalcinosis and in 16.7-20.8% of individuals with onset before 18 years of age, using gene panel sequencing of 30 genes known to cause nephrolithiasis/nephrocalcinosis. To overcome the limitations of panel sequencing, we utilized whole exome sequencing in 51 families, who presented before age 25 years with at least one renal stone or with a renal ultrasound finding of nephrocalcinosis to identify the underlying molecular genetic cause of disease. In 15 of 51 families, we detected a monogenic causative mutation by whole exome sequencing. A mutation in seven recessive genes (AGXT, ATP6V1B1, CLDN16, CLDN19, GRHPR, SLC3A1, SLC12A1), in one dominant gene (SLC9A3R1), and in one gene (SLC34A1) with both recessive and dominant inheritance was detected. Seven of the 19 different mutations were not previously described as disease-causing. In one family, a causative mutation in one of 117 genes that may represent phenocopies of nephrolithiasis-causing genes was detected. In nine of 15 families, the genetic diagnosis may have specific implications for stone management and prevention. Several factors that correlated with the higher detection rate in our cohort were younger age at onset of nephrolithiasis/nephrocalcinosis, presence of multiple affected members in a family, and presence of consanguinity. Thus, we established whole exome sequencing as an efficient approach toward a molecular genetic diagnosis in individuals with nephrolithiasis/nephrocalcinosis who manifest before age 25 years.

Analysis of 24 genes reveals a monogenic cause in 11.1% of cases with steroid-resistant nephrotic syndrome at a single center.

BACKGROUND: Steroid-resistant nephrotic syndrome (SRNS) is the second most frequent cause of end-stage renal disease (ESRD) among patients manifesting at under 25 years of age. We performed mutation analysis using a high-throughput PCR-based microfluidic technology in 24 single-gene causes of SRNS in a cohort of 72 families, who presented with SRNS before the age of 25 years. METHODS: Within an 18-month interval, we obtained DNA samples, pedigree information, and clinical information from 77 consecutive children with SRNS from 72 different families seen at Boston Children's Hospital (BCH). Mutation analysis was completed by combining high-throughput multiplex PCR with next-generation sequencing. We analyzed the sequences of 18 recessive and 6 dominant genes of SRNS in all 72 families for disease-causing variants. RESULTS: We identified the disease-causing mutation in 8 out of 72 (11.1%) families. Mutations were detected in the six genes: NPHS1 (2 out of 72), WT1 (2 out of 72), NPHS2, MYO1E, TRPC6, and INF2. Median age at onset was 4.1 years in patients without a mutation (range 0.5-18.8), and 3.2 years in those in whom the causative mutation was detected (range 0.1-14.3). Mutations in dominant genes presented with a median onset of 4.5 years (range 3.2-14.3). Mutations in recessive genes presented with a median onset of 0.5 years (range 0.1-3.2). CONCLUSION: Our molecular genetic diagnostic study identified underlying monogenic causes of steroid-resistant nephrotic syndrome in ~11% of patients with SRNS using a cost-effective technique. We delineated some of the therapeutic, diagnostic, and prognostic implications. Our study confirms that genetic testing is indicated in pediatric patients with SRNS.

Imaging in the diagnosis of pediatric urolithiasis.

Pediatric urolithiasis is an important and increasingly prevalent cause of pediatric morbidity and hospital admission. Ultrasound (US) is the recommended primary imaging modality for suspected urolithiasis in children. There is, however, widespread use of CT as a first-line study for abdominal pain in many institutions involved in pediatric care. The objective of this review is to outline state-of-the-art imaging modalities and methods for diagnosing urolithiasis in children. The pediatric radiologist plays a key role in ensuring that the appropriate imaging modality is performed in the setting of suspected pediatric urolithiasis. Our proposed imaging algorithm starts with US, and describes the optimal technique and indications for the use of CT. We emphasize the importance of improved communication with a greater collaborative approach between pediatric and general radiology departments so children undergo the appropriate imaging evaluation.