Protocolized polyoma BK viral load monitoring and high-dose immunoglobulin treatment in children after kidney transplant

Background

BKPyV virus nephropathy (BKPyVAN) is diagnosed in 5%-16% of pediatric renal transplant recipients (PRTR) and preceded by BKPyV-viruria and DNAemia. Despite the risk of irreversible transplant damage associated with BKPyVAN, evidence-based consensus guidelines for BKPyVAN prevention are still lacking. In this retrospective study, we examined the safety and efficacy of high-dose intravenous immunoglobulin (HD-IVIG) therapy for prevention of BKPyVAN in PRTR with significant BKPyV-viruria/DNAemia.

Methods

Between January 2013 and December 2022, all PRTR under our care underwent routine urine and blood testing for BKPyV viral load, using specific polymerase chain reaction (PCR). BKPyV DNAemia, with <103 copies/mL, with BKPyV viruria <107 copies/mL, with no evidence of BKPyVAN, were managed with 50% dose reduction of mycophenolate mofetil (MMF). Patients showing no decline in BKPyV viral load within two months of MMF dose reduction were managed with HD-IVIG (2 g/kg).

Results

Seventy patients were recruited during a ten-year period and 31/70 patients (44%) demonstrated significant post-transplantation BKPyV-viruria/DNAemia, while 13/31 (42%) patients were unresponsive to MMF dose reduction, and were administered HD-IVIG. Of these, 12/13 (92%) patients achieved BKPyV viral clearance within six months from completion of HD-IVIG therapy and 1/13 patient (8%) was unresponsive to HD-IVIG therapy, showing increased BKPyV viral load. There were no major adverse events associated with HD-IVIG, and none of our patients developed BKPyVAN during the study period.

Conclusions

Prophylactic HD-IVIG therapy in PRTR with significant BKPyV-viruria/DNAemia unresponsive to MMF dose reduction is safe and might be effective in preventing BKPyVAN. Our findings remain to be established by large-scale prospective studies.

Innate Immunity and CKD: Is There a Significant Association?

Chronic kidney disease (CKD) constitutes a worldwide epidemic, affecting approximately 10% of the global population, and imposes significant medical, psychological, and financial burdens on society. Individuals with CKD often face elevated morbidity and mortality rates, mainly due to premature cardiovascular events. Chronic inflammation has been shown to play a significant role in the progression of CKD, as well as in the acceleration of CKD-related complications, including atherosclerosis, cardiovascular disease (CVD), protein-energy wasting, and the aging process. Over the past two decades, a substantial body of evidence has emerged, identifying chronic inflammation as a central element of the uremic phenotype. Chronic inflammation has been shown to play a significant role in the progression of CKD, as well as in the acceleration of CKD-related complications in dialysis patients, including atherosclerosis, CVD, protein-energy wasting, and the aging process. Remarkably, chronic inflammation also impacts patients with CKD who have not yet required renal replacement therapy. While extensive research has been conducted on the involvement of both the adaptive and innate immune systems in the pathogenesis of CKD-related complications, this wealth of data has not yet yielded well-established, effective treatments to counteract this ongoing pathological process. In the following review, we will examine the established components of the innate immune system known to be activated in CKD and provide an overview of the current therapeutic approaches designed to mitigate CKD-related chronic inflammation.

Diagnostic Utility of Exome Sequencing Among Israeli Children With Kidney Failure

Introduction

Genetic etiologies are estimated to account for a large portion of chronic kidney diseases (CKD) in children. However, data are lacking regarding the true prevalence of monogenic etiologies stemming from an unselected population screen of children with advanced CKD.

Methods

We conducted a national multicenter prospective study of all Israeli pediatric dialysis units to provide comprehensive "real-world" evidence for the genetic basis of childhood kidney failure in Israel. We performed exome sequencing and assessed the genetic diagnostic yield.

Results

Between 2019 and 2022, we recruited approximately 88% (n = 79) of the children on dialysis from all 6 Israeli pediatric dialysis units. We identified genetic etiologies in 36 of 79 (45%) participants. The most common subgroup of diagnostic variants was in congenital anomalies of the kidney and urinary tract causing genes (e.g., EYA1, HNF1B, PAX2, COL4A1, and NFIA) which together explain 28% of all monogenic etiologies. This was followed by mutations in genes causing renal cystic ciliopathies (e.g., NPHP1, NPHP4, PKHD1, and BBS9), steroid-resistant nephrotic syndrome (e.g., LAGE3, NPHS1, NPHS2, LMX1B, and SMARCAL1) and tubulopathies (e.g., CTNS and AQP2). The genetic diagnostic yield was higher among Arabs compared to Jewish individuals (55% vs. 29%) and in children from consanguineous compared to nonconsanguineous families (63% vs. 29%). In 5 participants (14%) with genetic diagnoses, the molecular diagnosis did not correspond with the pre-exome diagnosis. Genetic diagnosis has a potential influence on clinical management in 27 of 36 participants (75%).

Conclusion

Exome sequencing in an unbiased Israeli nationwide dialysis-treated kidney failure pediatric cohort resulted in a genetic diagnostic yield of 45% and can often affect clinical decision making.

Reduced Electroretinogram Responses in Morphologically Normal Retina in Patients with Primary Hyperoxaluria Type 1

Purpose

To describe ocular findings in individuals with primary hyperoxaluria type 1 (PH1), focusing on the correlations between retinal anatomy and retinal function. To characterize the retinal alterations that occur at different disease stages by evaluating individuals with diverse degrees of renal impairment associated with PH1.

Design

A cross-sectional study.

Participants

Patients diagnosed with PH1 based on clinical criteria and genetic testing, treated in the Pediatric Nephrology Unit of the Ruth Children's Hospital, Rambam Health Care Campus, Haifa, Israel between 2013 and 2021.

Methods

The ophthalmological assessment included a slit-lamp biomicroscopy of the anterior and posterior segment or indirect ophthalmoscopy. Electroretinography was employed for assessment of the retinal function, and retinal imaging included spectral-domain OCT and fundus autofluorescence. A systematic evaluation of the disease stage was based on clinical criteria including physical examination, purposeful imaging (X-ray, echocardiography, and US abdomen), and laboratory tests as needed.

Main Outcome Measures

Anatomical and functional assessment of the retina in patients with PH1, and the relationship between retinal dysfunction and kidney impairment.

Results

A total of 16 eyes were examined in the study of 8 children ranging in age from 4 to 19 years. Four eyes (25%) showed normal structural and functional retinal findings, 8 eyes (50%) presented functional impairment in the absence of pathological structural findings, and 4 eyes (25%) had advanced retinal damage that manifested as significant morphological and functional impairment. There was no direct relationship between the severity of the renal disease and the severity of the retinal phenotype.

Conclusions

Subjects with PH1 present varying severity levels of the retinal phenotype, with possible discrepancy between the clinical retinal morphology and the retinal function noted on electroretinography. These findings raise questions about the molecular basis of the retinal manifestations in PH1. The presence of functional impairment in the absence of evident crystal deposition in the retina suggests that, in addition to oxalate crystal accumulation, other biomolecular processes may play a role in the development of retinopathy.

Dialysis in Israeli Children between 1990 and 2020: Trends and International Comparisons

BACKGROUND

Childhood kidney failure is a rare condition with worldwide clinical variability. We used a nationwide multicenter analysis to study the pretransplant course of the entire Israeli pediatric kidney failure population over 30 years.

METHODS

In this nationwide, population-based, historical cohort study, we analyzed medical and demographic data of all children treated with KRT and reported to the Israeli kidney failure registry in 1990-2020. Statistical analysis was performed with incidence rate corrected for age, ethnicity, and calendar year, using the appropriate age-related general population as denominator.

RESULTS

During the last 30 years, childhood incidence of kidney failure decreased. Average incidence in 2015-2019 was 9.1 cases per million age-related population (pmarp). Arab and Druze children exhibited higher kidney failure incidence rates than Jewish children (18.4 versus 7.0 cases pmarp for minorities versus Jews). The most common kidney failure etiologies among Arab and Jewish children were congenital anomalies of the kidney and urinary tract (approximately 27%), followed by cystic kidney diseases among Arab children (13%) and glomerulonephritis among Jewish children (16%). The most common etiology among Druze children was primary hyperoxaluria type 1 (33%). Israel's national health insurance provides access to primary health care to all citizens. Accordingly, waiting time for deceased-donor transplantation was equal between all ethnicities. Living-donor kidney transplantation rates among minority populations remained low in comparison with Jews over the entire study period. Although all patient groups demonstrated improvement in survival, overall survival rates were mainly etiology dependent.

CONCLUSIONS

In Israel, Arab and Druze children had a higher incidence of kidney failure, a unique etiological distribution, and a lower rate of living-donor kidney transplantations compared with Jewish children.

Lumasiran for Advanced Primary Hyperoxaluria Type 1: Phase 3 ILLUMINATE-C Trial

RATIONALE & OBJECTIVE

Lumasiran reduces urinary and plasma oxalate (POx) in patients with primary hyperoxaluria type 1 (PH1) and relatively preserved kidney function. ILLUMINATE-C evaluates the efficacy, safety, pharmacokinetics, and pharmacodynamics of lumasiran in patients with PH1 and advanced kidney disease.

STUDY DESIGN

Phase 3, open-label, single-arm trial.

SETTING & PARTICIPANTS

Multinational study; enrolled patients with PH1 of all ages, estimated glomerular filtration rate ≤45 mL/min/1.73 m² (if age ≥12 months) or increased serum creatinine level (if age <12 months), and POx ≥20 μmol/L at screening, including patients with or without systemic oxalosis.

INTERVENTION

Lumasiran administered subcutaneously; 3 monthly doses followed by monthly or quarterly weight-based dosing.

OUTCOME

Primary end point: percent change in POx from baseline to month 6 (cohort A; not receiving hemodialysis at enrollment) and percent change in predialysis POx from baseline to month 6 (cohort B; receiving hemodialysis at enrollment). Pharmacodynamic secondary end points: percent change in POx area under the curve between dialysis sessions (cohort B only); absolute change in POx; percent and absolute change in spot urinary oxalate-creatinine ratio; and 24-hour urinary oxalate adjusted for body surface area.

RESULTS

All patients (N = 21; 43% female; 76% White) completed the 6-month primary analysis period. Median age at consent was 8 (range, 0-59) years. For the primary end point, least-squares mean reductions in POx were 33.3% (95% CI, -15.2% to 81.8%) in cohort A (n = 6) and 42.4% (95% CI, 34.2%-50.7%) in cohort B (n = 15). Improvements were also observed in all pharmacodynamic secondary end points. Most adverse events were mild or moderate. No patient discontinued treatment or withdrew from the study. The most commonly reported lumasiran-related adverse events were injection-site reactions, all of which were mild and transient.

LIMITATIONS

Single-arm study without placebo control.

CONCLUSIONS

Lumasiran resulted in substantial reductions in POx with acceptable safety in patients with PH1 who have advanced kidney disease, supporting its efficacy and safety in this patient population.

FUNDING

Alnylam Pharmaceuticals.

TRIAL REGISTRATION

Registered at ClinicalTrials.gov with study number NCT04152200 and at EudraCT with study number 2019-001346-17.

PLAIN-LANGUAGE SUMMARY

Primary hyperoxaluria type 1 (PH1) is a rare genetic disease characterized by excessive hepatic oxalate production that frequently causes kidney failure. Lumasiran is an RNA interference therapeutic that is administered subcutaneously for the treatment of PH1. Lumasiran has been shown to reduce oxalate levels in the urine and plasma of patients with PH1 who have relatively preserved kidney function. In the ILLUMINATE-C study, the efficacy and safety of lumasiran were evaluated in patients with PH1 and advanced kidney disease, including a cohort of patients undergoing hemodialysis. During the 6-month primary analysis period, lumasiran resulted in substantial reductions in plasma oxalate with acceptable safety in patients with PH1 complicated by advanced kidney disease.

Efficacy and safety of lumasiran for infants and young children with primary hyperoxaluria type 1: 12-month analysis of the phase 3 ILLUMINATE-B trial

BACKGROUND

Primary hyperoxaluria type 1 (PH1) is a rare genetic disease that causes progressive kidney damage and systemic oxalosis due to hepatic overproduction of oxalate. Lumasiran demonstrated efficacy and safety in the 6-month primary analysis period of the phase 3, multinational, open-label, single-arm ILLUMINATE-B study of infants and children < 6 years old with PH1 (ClinicalTrials.gov: NCT03905694 (4/1/2019); EudraCT: 2018-004,014-17 (10/12/2018)). Outcomes in the ILLUMINATE-B extension period (EP) for patients who completed ≥ 12 months on study are reported here.

METHODS

Of the 18 patients enrolled in the 6-month primary analysis period, all entered the EP and completed ≥ 6 additional months of lumasiran treatment (median (range) duration of total exposure, 17.8 (12.7-20.5) months).

RESULTS

Lumasiran treatment was previously reported to reduce spot urinary oxalate:creatinine ratio by 72% at month 6, which was maintained at 72% at month 12; mean month 12 reductions in prespecified weight subgroups were 89%, 68%, and 71% for patients weighing < 10 kg, 10 to < 20 kg, and ≥ 20 kg, respectively. The mean reduction from baseline in plasma oxalate level was reported to be 32% at month 6, and this improved to 47% at month 12. Additional improvements were also seen in nephrocalcinosis grade, and kidney stone event rates remained low. The most common lumasiran-related adverse events were mild, transient injection-site reactions (3 patients (17%)).

CONCLUSIONS

Lumasiran treatment provided sustained reductions in urinary and plasma oxalate through month 12 across all weight subgroups, with an acceptable safety profile, in infants and young children with PH1. A higher resolution version of the Graphical abstract is available as Supplementary information.

FC035: Exome Sequencing of the Israeli Dialysis-Treated Pediatric Population Reveals Monogenic Etiology in ∼44% of Cases

BACKGROUND

Chronic kidney disease in children is estimated to be secondary to a monogenic etiology in ∼20% of patients and can arise from mutations in a multitude of different single-gene causes. Still, data are lacking on the true prevalence of genetic etiologies dates from a large scale unbiased population screen of children with advanced kidney disease.

METHOD

In order to provide comprehensive real-world evidence for monogenic etiologies of childhood end-stage kidney disease—on a national level—we initiated a nation-wide multicenter study of all pediatric Israeli dialysis units. Specifically, between 2020 and 2021, we recruited ∼90% (n = 66) of children on dialysis from all six dialysis units treating children in Israel. We conducted exome sequencing and diagnostic analysis for all patients. We assessed the diagnostic yield of genetic analysis and its relation to baseline clinical phenotypes.

RESULTS

Overall, the cohort comprises 66 individuals from different families with a first-degree consanguinity rate of 47%. Participants' mean age at renal replacement therapy initiation was 8.1 years (range 1-month to 20-years). Using exome sequencing we identified a genetic etiology in 29 out of 66 (44%) participants. The most common subgroup of diagnostic variants was in genes causing renal cystic ciliopathies (e.g. NPHP1, NPHP4, PKHD1 and BBS9), which together explain 31% of all monogenic etiologies. This was followed by mutations in genes causing CAKUT (e.g. EYA1, HNF1B, PAX2, COL4A1 and GREB1L), steroid-resistant nephrotic syndrome (e.g. LAGE3, NPHS1, NPHS2, LMX1B, SMARCAL1 and CRB2) and tubulopathies (e.g. CTNS, AQP2), which explain 21%, 21% and 17% of all genetic etiologies, respectively. The yield of exome sequencing was higher among non-Jewish compared with Jewish individuals (52% versus 29%) and in children from consanguineous families compared with non-consanguineous families (56% versus 31%). The final molecular diagnosis did not correspond with the pre-exome clinical diagnosis in 17% of cases.

CONCLUSION

Exome sequencing in an unbiased pediatric cohort with end-stage kidney disease yields a genetic diagnosis in 44% of cases and reveals many underappreciated monogenic etiologies. Surprisingly, renal cystic ciliopathies causing-genes were more common than CAKUT genes in our cohort. These results emphasize the importance of genetic testing among children with advanced chronic kidney disease and validate the role of exome sequencing as a standard routine diagnostic tool.

A Founder Mutation in EHD1 Presents with Tubular Proteinuria and Deafness

BACKGROUND

The endocytic reabsorption of proteins in the proximal tubule requires a complex machinery and defects can lead to tubular proteinuria. The precise mechanisms of endocytosis and processing of receptors and cargo are incompletely understood. EHD1 belongs to a family of proteins presumably involved in the scission of intracellular vesicles and in ciliogenesis. However, the relevance of EHD1 in human tissues, in particular in the kidney, was unknown.

METHODS

Genetic techniques were used in patients with tubular proteinuria and deafness to identify the disease-causing gene. Diagnostic and functional studies were performed in patients and disease models to investigate the pathophysiology.

RESULTS

We identified six individuals (5-33 years) with proteinuria and a high-frequency hearing deficit associated with the homozygous missense variant c.1192C>T (p.R398W) in EHD1. Proteinuria (0.7-2.1 g/d) consisted predominantly of low molecular weight proteins, reflecting impaired renal proximal tubular endocytosis of filtered proteins. Ehd1 knockout and Ehd1R398W/R398W knockin mice also showed a high-frequency hearing deficit and impaired receptor-mediated endocytosis in proximal tubules, and a zebrafish model showed impaired ability to reabsorb low molecular weight dextran. Interestingly, ciliogenesis appeared unaffected in patients and mouse models. In silico structural analysis predicted a destabilizing effect of the R398W variant and possible inference with nucleotide binding leading to impaired EHD1 oligomerization and membrane remodeling ability.

CONCLUSIONS

A homozygous missense variant of EHD1 causes a previously unrecognized autosomal recessive disorder characterized by sensorineural deafness and tubular proteinuria. Recessive EHD1 variants should be considered in individuals with hearing impairment, especially if tubular proteinuria is noted.

Phase 3 trial of lumasiran for primary hyperoxaluria type 1: A new RNAi therapeutic in infants and young children

PURPOSE

Primary hyperoxaluria type 1 (PH1) is a rare, progressive, genetic disease with limited treatment options. We report the efficacy and safety of lumasiran, an RNA interference therapeutic, in infants and young children with PH1.

METHODS

This single-arm, open-label, phase 3 study evaluated lumasiran in patients aged <6 years with PH1 and an estimated glomerular filtration rate >45 mL/min/1.73 m², if aged ≥12 months, or normal serum creatinine, if aged <12 months. The primary end point was percent change in spot urinary oxalate to creatinine ratio (UOx:Cr) from baseline to month 6. Secondary end points included proportion of patients with urinary oxalate ≤1.5× upper limit of normal and change in plasma oxalate.

RESULTS

All patients (N = 18) completed the 6-month primary analysis period. Median age at consent was 50.1 months. Least-squares mean percent reduction in spot UOx:Cr was 72.0%. At month 6, 50% of patients (9/18) achieved spot UOx:Cr ≤1.5× upper limit of normal. Least-squares mean percent reduction in plasma oxalate was 31.7%. The most common treatment-related adverse events were transient, mild, injection-site reactions.

CONCLUSION

Lumasiran showed rapid, sustained reduction in spot UOx:Cr and plasma oxalate and acceptable safety in patients aged <6 years with PH1, establishing RNA interference therapies as safe, effective treatment options for infants and young children.

[INTRAVENOUS IMMUNOGLOBULIN TREATMENT TO PREVENT BK NEPHROPATHY IN PEDIATRIC RENAL TRANSPLANT RECIPIENTS WITH BK VIRUS]

AIMS

In this retrospective study we examined the safety and efficacy of high-dose intravenous immunoglobulin (HD-IVIG) therapy in preventing BKVN in pediatric renal transplant recipients with BK-viremia/viruria.

BACKGROUND

BK virus nephropathy (BKVN) is diagnosed in 5-16% of pediatric renal transplant recipients and is preceded by BK viremia/viruria. Despite irreversible renal damage associated with BKVN, there is a lack of evidence-based guidelines for preventive measures in patients with BK viremia/viruria.

METHODS

All pediatric renal transplant recipients under our care underwent routine testing for urine and blood BK virus, using the polymerase chain reaction (PCR) technique. Patients exhibiting BK-viruria < 107 copies/milliliter (ml) and/or BK-viremia<103 copies/ml without any evidence of BKVN, were managed with 50% dose reduction of the immunosuppressive drug mycophenolate mofetil (MMF). Absence of BK viral load decline within two months from MMF dose reduction was managed with HD-IVIG (at 2 grams/kg body weight).

RESULTS

The study included 62 patients over a 6-year period; 31 patients (50%) showed BK-viremia/viruria; 13/31 patients (42%) suffered from significant and persistent BK-viremia/viruria, unresponsive to MMF dose reduction, and were managed with HD-IVIG; 12/13 (92%) showed significant BK viral load reduction within 6 months from HD-IVIG therapy. Except for transient headache, no patient exhibited major adverse effects to HD-IVIG therapy, and none developed overt BKVN during the study period.

CONCLUSIONS

Preventive HD-IVIG therapy in pediatric renal transplant recipients with BK viremia/viruria unresponsive to MMF dose reduction is safe and effective in preventing the development of BKVN. Additional large-scale studies are necessary to establish our findings.

Randomized Clinical Trial on the Long-Term Efficacy and Safety of Lumasiran in Patients With Primary Hyperoxaluria Type 1

Introduction

Primary hyperoxaluria type 1 (PH1) is a rare genetic disease caused by hepatic overproduction of oxalate, leading to kidney stones, nephrocalcinosis, kidney failure, and systemic oxalosis. In the 6-month double-blind period (DBP) of ILLUMINATE-A, a phase 3, randomized, placebo-controlled trial in patients with PH1 ≥6 years old, treatment with lumasiran, an RNA interference therapeutic, led to substantial reductions in urinary oxalate (UOx) levels.

Methods

We report data to month 12 in the extension period (EP) of ILLUMINATE-A, including patients who continued lumasiran (lumasiran/lumasiran) or crossed over from placebo to lumasiran (placebo/lumasiran).

Results

In the lumasiran/lumasiran group (n = 24), the reduction in 24-hour UOx level was sustained to month 12 (mean reduction from baseline, 66.9% at month 6; 64.1% at month 12). The placebo/lumasiran group (n = 13) had a similar time course and magnitude of 24-hour UOx reduction (mean reduction, 57.3%) after 6 months of lumasiran. Kidney stone event rates seemed to be lower after 6 months of lumasiran in both groups compared with the 12 months before consent, and this reduction was maintained at month 12 in the lumasiran/lumasiran group. At study start, 71% of patients in the lumasiran/lumasiran group and 92% in the placebo/lumasiran group had nephrocalcinosis. Nephrocalcinosis grade improved after 6 months of lumasiran in the lumasiran/lumasiran and placebo/lumasiran groups (13% and 8% of patients, respectively). After an additional 6 months of lumasiran, 46% of patients had improvement in nephrocalcinosis grade within the lumasiran/lumasiran group. Estimated glomerular filtration rate (eGFR) remained stable during the course of lumasiran treatment. The most common adverse events (AEs) related to lumasiran were mild, transient injection-site reactions (ISRs).

Conclusion

Long-term lumasiran treatment enabled sustained lowering of UOx levels with acceptable safety and encouraging results on clinical outcomes.

Relation of glomerular filtration to insulin resistance and related risk factors in obese children

BACKGROUND AND OBJECTIVE

Childhood obesity is associated with later development of significant renal morbidity. We evaluated the impact of the degree of insulin sensitivity on estimated glomerular filtration rate (eGFR) and determined the factors associated with eGFR in obese children. We further tested the relation of eGFR to clinical outcomes such as blood pressure and microalbuminuria.

MATERIALS AND METHODS

We evaluated the relation of whole body insulin sensitivity and estimated glomerular filtration rate (eGFR) across the spectrum of obesity in children and adolescents. eGFR was calculated using the iCARE formula, which has been validated in obese children with varying glucose tolerance.

RESULTS

1080 children and adolescents with overweight and obesity (701 females and 379 males) participated. Insulin sensitivity was a strongly negatively associated with (B = -2.72, p < 0.001) eGFR), even after adjustment for potential confounders. Male sex emerged to be significantly associated with eGFR with boys having greater values than girls (B = 18.82, p < 0.001). Age was a positively associated (B = 2.86, p < 0.001) with eGFR. Whole body and hepatic insulin sensitivity decreased across eGFR quartiles. Adjusted eGFR was tightly positively associated with systolic blood pressure (B = 0.09, p = 0.003) and negatively associated with the presence of microalbuminuria (B = -2.18, p = 0.04).

CONCLUSIONS

eGFR tends to increase with greater degrees of insulin resistance in children and adolescents representing hyperfiltration and is associated with cardiovascular risk factors. Longitudinal studies are needed to determine the natural history of childhood insulin resistance related hyperfiltration in regards to future kidney disease.

Phase 1/2 Study of Lumasiran for Treatment of Primary Hyperoxaluria Type 1: A Placebo-Controlled Randomized Clinical Trial

BACKGROUND AND OBJECTIVES

In the rare disease primary hyperoxaluria type 1, overproduction of oxalate by the liver causes kidney stones, nephrocalcinosis, kidney failure, and systemic oxalosis. Lumasiran, an RNA interference therapeutic, suppresses glycolate oxidase, reducing hepatic oxalate production. The objective of this first-in-human, randomized, placebo-controlled trial was to evaluate the safety, pharmacokinetic, and pharmacodynamic profiles of lumasiran in healthy participants and patients with primary hyperoxaluria type 1.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This phase 1/2 study was conducted in two parts. In part A, healthy adults randomized 3:1 received a single subcutaneous dose of lumasiran or placebo in ascending dose groups (0.3-6 mg/kg). In part B, patients with primary hyperoxaluria type 1 randomized 3:1 received up to three doses of lumasiran or placebo in cohorts of 1 or 3 mg/kg monthly or 3 mg/kg quarterly. Patients initially assigned to placebo crossed over to lumasiran on day 85. The primary outcome was incidence of adverse events. Secondary outcomes included pharmacokinetic and pharmacodynamic parameters, including measures of oxalate in patients with primary hyperoxaluria type 1. Data were analyzed using descriptive statistics.

RESULTS

Thirty-two healthy participants and 20 adult and pediatric patients with primary hyperoxaluria type 1 were enrolled. Lumasiran had an acceptable safety profile, with no serious adverse events or study discontinuations attributed to treatment. In part A, increases in mean plasma glycolate concentration, a measure of target engagement, were observed in healthy participants. In part B, patients with primary hyperoxaluria type 1 had a mean maximal reduction from baseline of 75% across dosing cohorts in 24-hour urinary oxalate excretion. All patients achieved urinary oxalate levels ≤1.5 times the upper limit of normal.

CONCLUSIONS

Lumasiran had an acceptable safety profile and reduced urinary oxalate excretion in all patients with primary hyperoxaluria type 1 to near-normal levels.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Study of Lumasiran in Healthy Adults and Patients with Primary Hyperoxaluria Type 1, NCT02706886.

A Novel Homozygous In-Frame Deletion in Complement Factor 3 Underlies Early-Onset Autosomal Recessive Atypical Hemolytic Uremic Syndrome - Case Report

Background and Objectives

Atypical hemolytic uremic syndrome (aHUS) is mostly attributed to dysregulation of the alternative complement pathway (ACP) secondary to disease-causing variants in complement components or regulatory proteins. Hereditary aHUS due to C3 disruption is rare, usually caused by heterozygous activating mutations in the C3 gene, and transmitted as autosomal dominant traits. We studied the molecular basis of early-onset aHUS, associated with an unusual finding of a novel homozygous activating deletion in C3.

Design, Setting, Participants, & Measurements

A male neonate with eculizumab-responsive fulminant aHUS and C3 hypocomplementemia, and six of his healthy close relatives were investigated. Genetic analysis on genomic DNA was performed by exome sequencing of the patient, followed by targeted Sanger sequencing for variant detection in his close relatives. Complement components analysis using specific immunoassays was performed on frozen plasma samples from the patient and mother.

Results

Exome sequencing revealed a novel homozygous variant in exon 26 of C3 (c.3322_3333del, p.Ile1108_Lys1111del), within the highly conserved thioester-containing domain (TED), fully segregating with the familial disease phenotype, as compatible with autosomal recessive inheritance. Complement profiling of the patient showed decreased C3 and FB levels, with elevated levels of the terminal membrane attack complex, while his healthy heterozygous mother showed intermediate levels of C3 consumption.

Conclusions

Our findings represent the first description of aHUS secondary to a novel homozygous deletion in C3 with ensuing unbalanced C3 over-activation, highlighting a critical role for the disrupted C3-TED domain in the disease mechanism.

Lumasiran, an RNAi Therapeutic for Primary Hyperoxaluria Type 1

BACKGROUND

Primary hyperoxaluria type 1 (PH1) is a rare genetic disease caused by hepatic overproduction of oxalate that leads to kidney stones, nephrocalcinosis, kidney failure, and systemic oxalosis. Lumasiran, an investigational RNA interference (RNAi) therapeutic agent, reduces hepatic oxalate production by targeting glycolate oxidase.

METHODS

In this double-blind, phase 3 trial, we randomly assigned (in a 2:1 ratio) patients with PH1 who were 6 years of age or older to receive subcutaneous lumasiran or placebo for 6 months (with doses given at baseline and at months 1, 2, 3, and 6). The primary end point was the percent change in 24-hour urinary oxalate excretion from baseline to month 6 (mean percent change across months 3 through 6). Secondary end points included the percent change in the plasma oxalate level from baseline to month 6 (mean percent change across months 3 through 6) and the percentage of patients with 24-hour urinary oxalate excretion no higher than 1.5 times the upper limit of the normal range at month 6.

RESULTS

A total of 39 patients underwent randomization; 26 were assigned to the lumasiran group and 13 to the placebo group. The least-squares mean difference in the change in 24-hour urinary oxalate excretion (lumasiran minus placebo) was -53.5 percentage points (P<0.001), with a reduction in the lumasiran group of 65.4% and an effect seen as early as month 1. The between-group differences for all hierarchically tested secondary end points were significant. The difference in the percent change in the plasma oxalate level (lumasiran minus placebo) was -39.5 percentage points (P<0.001). In the lumasiran group, 84% of patients had 24-hour urinary oxalate excretion no higher than 1.5 times the upper limit of the normal range at month 6, as compared with 0% in the placebo group (P<0.001). Mild, transient injection-site reactions were reported in 38% of lumasiran-treated patients.

CONCLUSIONS

Lumasiran reduced urinary oxalate excretion, the cause of progressive kidney failure in PH1. The majority of patients who received lumasiran had normal or near-normal levels after 6 months of treatment. (Funded by Alnylam Pharmaceuticals; ILLUMINATE-A ClinicalTrials.gov number, NCT03681184.).

A novel loss-of-function mutation in LACC1 underlies hereditary juvenile arthritis with extended intra-familial phenotypic heterogeneity

OBJECTIVE

To investigate phenotypic and molecular characteristics of a consanguineous family with autosomal-recessive, polyarticular, juvenile idiopathic arthritis (JIA) with extra-articular manifestations, including renal amyloidosis and Crohn's disease, associated with a novel homozygous truncating variant in LACC1.

METHODS

Whole exome sequencing (WES) or targeted Sanger verification were performed in 15 participants. LACC1 expression and cytokine array were analyzed in patient-derived and CRISPR/Cas9-generated LACC1-knockout macrophages (Mϕ).

RESULTS

A homozygous truncating variant (p.Glu348Ter) in LACC1 was identified in three affected and one asymptomatic family member, and predicted harmful by causing premature stop of the LACC1 protein sequences, and by absence from ethnically-matched controls and public variation databases. Expression studies in patient-derived macrophages (Mϕ) showed no endogenous p. Glu348Ter-LACC1 RNA transcription or protein expression, compatible with nonsense-mediated mRNA decay. WES analysis in the asymptomatic homozygous subject for p. Glu348Ter-LACC1 detected an exclusive heterozygous variant (p.Arg928Gln) in complement component C5. Further complement activity analysis suggested a protective role for the p. Arg928Gln-C5 variant as a phenotypic modifier of LACC1-associated disease. Finally, cytokine profile analysis indicated increased levels of pro-inflammatory cytokines in LACC1-disrupted as compared with wild-type Mϕ.

CONCLUSIONS

Our findings reinforce the role of LACC1 disruption in autosomal-recessive JIA, extend the clinical spectrum and intra-familial heterogeneity of the disease-associated phenotype, indicate a modulatory effect of complement factor C5 on phenotypic severity, and suggest an inhibitory role for wild-type LACC1 on pro-inflammatory pathways.

LB002ILLUMINATE-A, A PHASE 3 STUDY OF LUMASIRAN, AN INVESTIGATIONAL RNAI THERAPEUTIC, IN CHILDREN AND ADULTS WITH PRIMARY HYPEROXALURIA TYPE 1 (PH1)

Background and Aims

PH1 is a rare genetic disorder characterized by hepatic oxalate overproduction, leading to recurrent kidney stones, nephrocalcinosis, progressive kidney failure, and multiorgan damage from systemic oxalosis. There are no approved pharmacologic therapies for PH1. Lumasiran is a subcutaneously-administered investigational RNAi therapeutic that targets glycolate oxidase to reduce hepatic oxalate production. We report the first results from the six-month, double-blind period of ILLUMINATE-A, a randomized, placebo-controlled Phase 3 study to evaluate lumasiran in patients with PH1.

Method

Key inclusion criteria: age≥6 years, 24hr urinary oxalate (UOx)≥0.70 mmol/24hr/1.73m2, confirmed PH1 diagnosis, eGFR≥30 mL/min/1.73m2. Randomization: 2:1; lumasiran (n=26), placebo (n=13). Dosing: 3 mg/kg monthly×3, then quarterly. Primary endpoint: percent change in 24hr UOx excretion from baseline to month (M) 6. Primary comparison: least square (LS) mean treatment difference in percent change from baseline (average of M3-6).

Results

Lumasiran led to a statistically significant percent reduction in 24hr UOx excretion compared to placebo: the LS mean change from baseline to M6 (average of M3-6) was −65.4% with lumasiran and −11.8% with placebo (LS mean difference: −53.5%; p=1.7 × 10−14). Subgroup analyses of the primary endpoint showed a consistent effect of lumasiran across age, baseline UOx, eGFR, and concomitant pyridoxine use. Lumasiran led to statistically significant improvements in all hierarchically tested secondary endpoints, including: proportion of lumasiran-treated patients that achieved normalization or near-normalization of 24hr UOx at M6 (84% vs 0% of placebo-treated patients, p=8.3 × 10−7), and percent change in plasma oxalate from baseline to M6 (average of months 3-6) (-39.5%, p=2.9 × 10−8). There were no serious or severe adverse events. The most common adverse events related to lumasiran were mild, transient injection site reactions.

Conclusion

Lumasiran resulted in clinically meaningful, rapid, sustained, and statistically significant reductions in urinary and plasma oxalate levels compared to placebo during the six-month double-blind period. Lumasiran has a favorable safety profile.

Clinical Heterogeneity and Phenotypic Expansion of NaPi-IIa-Associated Disease

CONTEXT

NaPi-IIa, encoded by SLC34A1, is a key phosphate transporter in the mammalian proximal tubule and plays a cardinal role in renal phosphate handling. NaPi-IIa impairment has been linked to various overlapping clinical syndromes, including hypophosphatemic nephrolithiasis with osteoporosis, renal Fanconi syndrome with chronic kidney disease, and, most recently, idiopathic infantile hypercalcemia and nephrocalcinosis.

OBJECTIVES

We studied the molecular basis of idiopathic infantile hypercalcemia with partial proximal tubulopathy in two apparently unrelated patients of Israeli and Turkish descent.

DESIGN

Genetic analysis in two affected children and their close relatives was performed using whole-exome sequencing, followed by in vitro localization and trafficking analysis of mutant NaPi-IIa.

RESULTS

Mutation and haplotype analyses in both patients revealed a previously described homozygous loss-of-function inserted duplication (p.I154_V160dup) in NaPi-IIa, which is inherited identical-by-descent from a common ancestor. The shared mutation was originally reported by our team in two adult siblings with renal Fanconi syndrome, hypophosphatemic bone disease, and progressive renal failure who are family members of one of the infants reported herein. In vitro localization assays and biochemical analysis of p.I154_V160dup and of additional NaPi-IIa mutants harboring a trafficking defect indicate aberrant retention at the endoplasmic reticulum in an immature and underglycosylated state, leading to premature proteasomal degradation.

CONCLUSIONS

Our findings expand the phenotypic spectrum of NaPi-IIa disruption, reinforce its link with proximal tubular impairment, enable longitudinal study of the natural history of the disease, and shed light on cellular pathways associated with loss of function and impaired trafficking of NaPi-IIa mutants.

[GENETIC DISORDERS OF RENAL PHOSPHATE HANDLING]

Hereditary disorders of renal phosphate handling comprise a diverse group of genetic diseases, usually characterized by excessive urinary phosphate wasting and a negative phosphate balance. In the minority of cases, perturbations of renal phosphate handling are associated with excessive urinary phosphate reabsorption, leading to pathological hyperphosphatemia. Inorganic phosphate is an essential mineral in the human body, playing a crucial role in cellular metabolism and skeletal mineralization. Whole body phosphate balance is maintained by a highly controlled equilibrium between intestinal uptake, skeletal deposition and renal excretion. The human kidney plays a crucial role in phosphate homeostasis. The bulk filtered phosphate is reabsorbed in the renal proximal tubule by two specialized phosphate transporters, NaPi-IIa and NaPi-IIc. Phosphate balance is regulated by dietary phosphate intake, and by the action of the parathyroid hormone, vitamin D3 and fibroblast growth factor-23 (FGF-23). All these regulators exert their effect by modulating the activity of the proximal-tubular phosphate transporters, NaPi-IIa and NaPi-IIc. Based on the versatile molecular mechanism underlying various renal phosphate wasting disorders, these diseases can be divided into three main subgroups: (1) primary impairment of proximal tubular phosphate transporters; (2) disorders of FGF-23 metabolism; (3) generalized dysfunction of the proximal tubule, also known as renal Fanconi syndrome. The clinical similarity between various renal phosphate wasting disorders, combined with their rarity, pose a diagnostic and therapeutic challenge. Recent advancement in molecular biology has led to the identification of the genetic basis of many disorders in this group, has improved our understanding of underlying disease mechanisms, and enables accurate genetic diagnosis. Nevertheless, the current therapy of most renal phosphate wasting disorders is mainly supportive, with limited capacity to change their natural course.

Mutations in KEOPS-complex genes cause nephrotic syndrome with primary microcephaly

Galloway-Mowat syndrome (GAMOS) is an autosomal-recessive disease characterized by the combination of early-onset nephrotic syndrome (SRNS) and microcephaly with brain anomalies. Here we identified recessive mutations in OSGEP, TP53RK, TPRKB, and LAGE3, genes encoding the four subunits of the KEOPS complex, in 37 individuals from 32 families with GAMOS. CRISPR-Cas9 knockout in zebrafish and mice recapitulated the human phenotype of primary microcephaly and resulted in early lethality. Knockdown of OSGEP, TP53RK, or TPRKB inhibited cell proliferation, which human mutations did not rescue. Furthermore, knockdown of these genes impaired protein translation, caused endoplasmic reticulum stress, activated DNA-damage-response signaling, and ultimately induced apoptosis. Knockdown of OSGEP or TP53RK induced defects in the actin cytoskeleton and decreased the migration rate of human podocytes, an established intermediate phenotype of SRNS. We thus identified four new monogenic causes of GAMOS, describe a link between KEOPS function and human disease, and delineate potential pathogenic mechanisms.

A Dominant Mutation in Nuclear Receptor Interacting Protein 1 Causes Urinary Tract Malformations via Dysregulation of Retinoic Acid Signaling

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most common cause of CKD in the first three decades of life. However, for most patients with CAKUT, the causative mutation remains unknown. We identified a kindred with an autosomal dominant form of CAKUT. By whole-exome sequencing, we identified a heterozygous truncating mutation (c.279delG, p.Trp93fs*) of the nuclear receptor interacting protein 1 gene (NRIP1) in all seven affected members. NRIP1 encodes a nuclear receptor transcriptional cofactor that directly interacts with the retinoic acid receptors (RARs) to modulate retinoic acid transcriptional activity. Unlike wild-type NRIP1, the altered NRIP1 protein did not translocate to the nucleus, did not interact with RARα, and failed to inhibit retinoic acid-dependent transcriptional activity upon expression in HEK293 cells. Notably, we also showed that treatment with retinoic acid enhanced NRIP1 binding to RARα RNA in situ hybridization confirmed Nrip1 expression in the developing urogenital system of the mouse. In explant cultures of embryonic kidney rudiments, retinoic acid stimulated Nrip1 expression, whereas a pan-RAR antagonist strongly reduced it. Furthermore, mice heterozygous for a null allele of Nrip1 showed a CAKUT-spectrum phenotype. Finally, expression and knockdown experiments in Xenopus laevis confirmed an evolutionarily conserved role for NRIP1 in renal development. These data indicate that dominant NRIP1 mutations can cause CAKUT by interference with retinoic acid transcriptional signaling, shedding light on the well documented association between abnormal vitamin A levels and renal malformations in humans, and suggest a possible gene-environment pathomechanism in this disease.

APOL1-Mediated Cell Injury Involves Disruption of Conserved Trafficking Processes

APOL1 harbors C-terminal sequence variants (G1 and G2), which account for much of the increased risk for kidney disease in sub-Saharan African ancestry populations. Expression of the risk variants has also been shown to cause injury to podocytes and other cell types, but the underlying mechanisms are not understood. We used Drosophila melanogaster and Saccharomyces cerevisiae to help clarify these mechanisms. Ubiquitous expression of the human APOL1 G1 and G2 disease risk alleles caused near-complete lethality in D. melanogaster, with no effect of the G0 nonrisk APOL1 allele, corresponding to the pattern of human disease risk. We also observed a congruent pattern of cellular damage with tissue-specific expression of APOL1. In particular, expression of APOL1 risk variants in D. melanogaster nephrocytes caused cell-autonomous accumulation of the endocytic tracer atrial natriuretic factor-red fluorescent protein at early stages and nephrocyte loss at later stages. We also observed differential toxicity of the APOL1 risk variants compared with the APOL1 nonrisk variants in S. cerevisiae, including impairment of vacuole acidification. Yeast strains defective in endosomal trafficking or organelle acidification but not those defective in autophagy displayed augmented APOL1 toxicity with all isoforms. This pattern of differential injury by the APOL1 risk alleles compared with the nonrisk alleles across evolutionarily divergent species is consistent with an impairment of conserved core intracellular endosomal trafficking processes. This finding should facilitate the identification of cell injury pathways and corresponding therapeutic targets of interest in these amenable experimental platforms.

A novel homozygous splice site mutation in NALCN identified in siblings with cachexia, strabismus, severe intellectual disability, epilepsy and abnormal respiratory rhythm

We studied three siblings, born to consanguineous parents who presented with severe intellectual disability, cachexia, strabismus, seizures and episodes of abnormal respiratory rhythm. Whole exome sequencing led to identification of a novel homozygous splice site mutation, IVS29-1G > A in the NALCN gene, that resulted in aberrant transcript in the patients. NALCN encodes a voltage-independent cation channel, involved in regulation of neuronal excitability. Three homozygous mutations in the NALCN gene were previously identified in only eight patients with severe hypotonia, speech impairment, cognitive delay, constipation and Infantile-Neuroaxonal-dystrophy- like symptoms. Our patients broaden the clinical spectrum associated with recessive mutations in NALCN, featuring also disrupted respiratory rhythm mimicking homozygous Nalcn knockout mice.

Long-term hemodialysis therapy in neonates and infants with end-stage renal disease: a 16-year experience and outcome

BACKGROUND

Peritoneal dialysis is the preferred mode of renal replacement therapy in infants with end-stage renal disease (ESRD). Hemodialysis (HD) is seldom used in neonates and infants due to the risk of major complications in the very young.

METHODS

Demographic, clinical, laboratory, and imaging data on all infants younger than 12 months with ESRD who received HD in our Pediatric Dialysis Unit between January 1997 and June 2013 were analyzed.

RESULTS

Eighteen infants (n = 6 male) with ESRD (median age 3 months; median weight 4.06 kg) received HD through a central venous catheter (CVC) for a total of 543 months (median duration per infant 16 months). Seven of the infants (39%) were neonates, and five (28%) had serious comorbidities. There were five episodes of CVC infection, which is a rate of 0.3/1000 CVC days. Median catheter survival time was 320 days. Most infants had good oral intake, and only four (22%) required a gastric tube; 14 (78%) infants displayed normal growth. Fourteen (78%) infants had hypertension, of whom four (22%) had severe cardiac complications; eight (44%) showed delayed psychomotor development. Eleven (61%) of the infants, including six (86%) of the neonates, survived. Five (28%) infants underwent renal transplantation; 10-year graft survival was 80%.

CONCLUSIONS

Based on these results, long-term HD in neonates and infants with ESRD is technically feasible, can be implemented without major complications, carries a very low rate of CVC infection and malfunction, and results in adequate nutrition, good growth, as well as good kidney graft and patient survivals. Future efforts should aim to prevent hypertension and its cardiac sequelae, improve neurodevelopmental outcome, and lower mortality rate in these infants.

Fanconi-Bickel syndrome and autosomal recessive proximal tubulopathy with hypercalciuria (ARPTH) are allelic variants caused by GLUT2 mutations

CONTEXT

Many inherited disorders of calcium and phosphate homeostasis are unexplained at the molecular level.

OBJECTIVE

The objective of the study was to identify the molecular basis of phosphate and calcium abnormalities in two unrelated, consanguineous families.

PATIENTS

The affected members in family 1 presented with rickets due to profound urinary phosphate-wasting and hypophosphatemic rickets. In the previously reported family 2, patients presented with proximal renal tubulopathy and hypercalciuria yet normal or only mildly increased urinary phosphate excretion.

METHODS

Genome-wide linkage scans and direct nucleotide sequence analyses of candidate genes were performed. Transport of glucose and phosphate by glucose transporter 2 (GLUT2) was assessed using Xenopus oocytes. Renal sodium-phosphate cotransporter 2a and 2c (Npt2a and Npt2c) expressions were evaluated in transgenically rescued Glut2-null mice (tgGlut2-/-).

RESULTS

In both families, genetic mapping and sequence analysis of candidate genes led to the identification of two novel homozygous mutations (IVS4-2A>G and R124S, respectively) in GLUT2, the gene mutated in Fanconi-Bickel syndrome, a rare disease usually characterized by renal tubulopathy, impaired glucose homeostasis, and hepatomegaly. Xenopus oocytes expressing the [R124S]GLUT2 mutant showed a significant reduction in glucose transport, but neither wild-type nor mutant GLUT2 facilitated phosphate import or export; tgGlut2-/- mice demonstrated a profound reduction of Npt2c expression in the proximal renal tubules.

CONCLUSIONS

Homozygous mutations in the facilitative glucose transporter GLUT2, which cause Fanconi-Bickel syndrome, can lead to very different clinical and biochemical findings that are not limited to mild proximal renal tubulopathy but can include significant hypercalciuria and highly variable degrees of urinary phosphate-wasting and hypophosphatemia, possibly because of the impaired proximal tubular expression of Npt2c.

Gitelman's syndrome: a pathophysiological and clinical update

Gitelman's syndrome (GS), also known as familial hypokalemic hypomagnesemia, is a rare autosomal recessive hereditary salt-losing tubulopathy, characterized by hypokalemic metabolic alkalosis, hypomagnesemia, and hypocalciuria, which is usually caused by mutations in the SLC12A3 gene encoding the thiazide-sensitive sodium chloride contrasporter. Because 18-40% of suspected GS patients carry only one SLC12A3 mutant allele, large genomic rearrangements must account for unidentified mutations. The clinical manifestations of GS are highly variable in terms of age at presentation, severity of symptoms, and biochemical abnormalities. Molecular analysis in our sibling's patients revealed compound heterozygous mutations in the coding region of SLC12A3 as underlying their disease. Such compound heterozygosity can result in disease phenotype for such loss of function mutations in the absence of homozygosis through consanguineous inheritance of mutant alleles, identical by descent. Missense mutations account for approximately 70% of the mutations in GS, and there is a predisposition to large rearrangements caused by the presence of repeated sequences within the SLC12A3. We report two adult male siblings of Jewish origin with late onset GS, who presented in their fifth decade of life with muscle weakness, hypokalemia, hypomagnesaemia, and metabolic alkalosis. Rapid clinical and biochemical improvement was achieved by replacement therapy with potassium and magnesium.

Low infection rates and prolonged survival times of hemodialysis catheters in infants and children

BACKGROUND AND OBJECTIVES

Hemodialysis (HD) catheter-related complications are regarded as the main cause of HD failure in infants and children with ESRD. In this study, we determined HD catheter infection rates and survival times in children.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We analyzed demographic, clinical, laboratory, and microbiologic data on all infants and children with ESRD who received HD therapy through a tunneled central venous catheter (CVC) in our Pediatric Dialysis Unit between January 2001 and December 2009. Our strict care of HD-CVCs makes no use of any kind of prophylactic antibiotic therapy.

RESULTS

Twenty-nine children with ESRD (median age, 10 years) received HD through a CVC, for a total of 22,892 days during the study period. Eleven (38%) children were infants (<1 year of age) who received HD for a cumulative 3779 days (16% of total). Fifty-nine CVCs were inserted, of which 13 (22%) were in infants. There were 12 episodes of CVC infection-a rate of 0.52/1000 CVC days. Four (33%) episodes occurred in infants-a rate of 1.06/1000 CVC days. Only three (5%) of the CVCs were removed because of infection. Median catheter survival time for all children was 310 days and for infants was 211 days.

CONCLUSIONS

Very low CVC infection rates (one infection per 5 CVC years) and prolonged CVC survival times (around 1 year) are achievable in infants and children with ESRD receiving HD therapy by adhering to a strict catheter management protocol and without using prophylactic antibiotic therapy.

Mutations in DHDPSL are responsible for primary hyperoxaluria type III

Primary hyperoxaluria (PH) is an autosomal-recessive disorder of endogenous oxalate synthesis characterized by accumulation of calcium oxalate primarily in the kidney. Deficiencies of alanine-glyoxylate aminotransferase (AGT) or glyoxylate reductase (GRHPR) are the two known causes of the disease (PH I and II, respectively). To determine the etiology of an as yet uncharacterized type of PH, we selected a cohort of 15 non-PH I/PH II patients from eight unrelated families with calcium oxalate nephrolithiasis for high-density SNP microarray analysis. We determined that mutations in an uncharacterized gene, DHDPSL, on chromosome 10 cause a third type of PH (PH III). To overcome the difficulties in data analysis attributed to a state of compound heterozygosity, we developed a strategy of "heterozygosity mapping"-a search for long heterozygous patterns unique to all patients in a given family and overlapping between families, followed by reconstruction of haplotypes. This approach enabled us to determine an allelic fragment shared by all patients of Ashkenazi Jewish descent and bearing a 3 bp deletion in DHDPSL. Overall, six mutations were detected: four missense mutations, one in-frame deletion, and one splice-site mutation. Our assumption is that DHDPSL is the gene encoding 4-hydroxy-2-oxoglutarate aldolase, catalyzing the final step in the metabolic pathway of hydroxyproline.

A loss-of-function mutation in NaPi-IIa and renal Fanconi's syndrome

We describe two siblings from a consanguineous family with autosomal recessive Fanconi's syndrome and hypophosphatemic rickets. Genetic analysis revealed a homozygous in-frame duplication of 21 bp in SLC34A1, which encodes the renal sodium-inorganic phosphate cotransporter NaPi-IIa, as the causative mutation. Functional studies in Xenopus laevis oocytes and in opossum kidney cells indicated complete loss of function of the mutant NaPi-IIa, resulting from failure of the transporter to reach the plasma membrane. These findings show that disruption of the human NaPi-IIa profoundly impairs overall renal phosphate reabsorption and proximal-tubule function and provide evidence of the critical role of NaPi-IIa in human renal phosphate handling.

A broad spectrum of developmental delay in a large cohort of prolidase deficiency patients demonstrates marked interfamilial and intrafamilial phenotypic variability

Prolidase deficiency (PD) is a rare, pan-ethnic, autosomal recessive disease with a broad phenotypic spectrum. Seventeen causative mutations in the PEPD gene have been reported worldwide. The purpose of this study is to characterize, clinically and molecularly, 20 prolidase deficient patients of Arab Moslem and Druze origin from 10 kindreds residing in northern Israel. All PD patients manifested developmental delay and facial dysmorphism. Typical PD dermatological symptoms, splenomegaly, and recurrent respiratory infections presented in varying degrees. Two patients had systemic lupus erythematosus (SLE), and one a novel cystic fibrosis phenotype. Direct DNA sequencing revealed two novel missense mutations, A212P and L368R. In addition, a previously reported S202F mutation was detected in 17 patients from seven Druze and three Arab Moslem kindreds. Patients homozygous for the S202F mutation manifest considerable interfamilial and intrafamilial phenotypic variability. The high prevalence of this mutation among Arab Moslems and Druze residing in northern Israel, and the presence of an identical haplotype along 500,000 bp in patients and their parents, suggests a founder event tracing back to before the breakaway of the Druze from mainstream Moslem society.

Early performance of voiding cystourethrogram after urinary tract infection in children

BACKGROUND

Voiding cystourethrogram is performed 3-6 weeks after urinary tract infection. This prolongs the interval of prophylactics, reducing the likelihood of having to perform the procedure.

OBJECTIVES

To investigate the yield and potential risks/benefits of early compared to late performance of VCUG after UTI.

METHODS

We conducted a prospective study of 84 previously healthy children < 5 years old admitted from October 2001 to November 2002 with first documented UTI. We then divided the 78 patients who had VCUG into two groups and compared them to a control group: group A--49 children in whom VCUG was performed within 10 days, group B--29 children in whom VCUG was performed > 10 days after UTI, and a historical control group C--82 children in whom VCUG was performed > 4 weeks following UTI.

RESULTS

VCUG was performed in 48/48 (100%), 6/35 patients (17.1%) and 34/116 patients (29.3%), and vesicoureteral reflux was demonstrated in 38.8%, 37.9% and 39% in groups A, B and C respectively. No significant difference was found between these groups in terms of incidence of VUR and severity and grading of reflux within each group. One case of UTI secondary to VCUG occurred in a patient in whom the procedure was performed 4 months after the diagnosis.

CONCLUSIONS

Performing VCUG early does not influence the detection rate, severity of the VUR, or risk of secondary infection; it shortens the period of prophylactic use and increases performance rate of VCUG, thereby minimizing the risk of failure to detect VUR. The traditional recommendation of performing VCUG 3-6 weeks after the diagnosis of UTI should be reevaluated.

A novel missense mutation in SLC5A2 encoding SGLT2 underlies autosomal-recessive renal glucosuria and aminoaciduria

BACKGROUND

Familial renal glucosuria (FRG) is an isolated disorder of proximal tubular glucose transport, characterized by abnormal urinary glucose excretion in the presence of normal blood glucose levels. Generalized aminoaciduria has not generally been considered a feature of this disorder. FRG has recently been shown to result from mutations in SLC5A2, encoding the kidney-specific low-affinity/high-capacity Na+/glucose cotransporter, SGLT2. The purpose of this study was to examine the phenotypic and genetic characteristics of three unrelated consanguineous families with FRG accompanied by aminoaciduria.

METHODS

Six children with autosomal-recessive FRG and 12 unaffected family members were evaluated at the clinical and molecular levels. DNA sequence analysis of the entire coding sequence of SLC5A2 was performed in all affected individuals. Haplotype analysis using four polymorphic markers flanking SLC5A2 was performed in all study participants.

RESULTS

All affected children were asymptomatic, but displayed massive glucosuria (83 to 169 g/1.73 m(2)/day) accompanied by generalized aminoaciduria. Sequence analysis in all patients revealed a novel homozygous missense mutation in exon 8 of SLC5A2, resulting in a lysine to arginine substitution at position 321 of SGLT2 amino acid sequence (K321R). The mutation was confirmed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis and was found to completely cosegregate with the FRG phenotype. Haplotype analysis is consistent with identity by descent for the mutation. The K321 residue, presumed to be located in the eighth transmembrane domain of SGLT2, is highly conserved across SGLT homologues.

CONCLUSION

Our findings confirm that mutations in SLC5A2 result in autosomal-recessive FRG. The severe glucosuria in homozygotes for the K321R mutation highlights the importance of the eighth SGLT2 transmembrane domain for normal glucose transport. We suggest that the generalized aminoaciduria accompanying FRG is a consequence of the severe impairment in glucose reabsorption, and is probably not directly related to the SGLT2 mutation. The exact role of the aberrant glucose transport in the pathogenesis of aminoaciduria remains to be established.

Autosomal recessive renal proximal tubulopathy and hypercalciuria: a new syndrome

BACKGROUND

The best described primary inherited proximal tubulopathies include X-linked hypercalciuric nephrolithiasis (XLHN), caused by a mutation in the chloride channel gene CLCN5, and classic Fanconi's syndrome, the genetic basis of which is unknown. The aim of this study is to examine the clinical, biochemical, and genetic characteristics of a highly consanguineous Druze family with autosomal recessive proximal tubulopathy and hypercalciuria (ARPTH), a syndrome not reported previously.

METHODS

Three children (2 girls, 1 boy) of the family referred for evaluation of renal glycosuria and hypercalciuria and 10 of their close relatives were evaluated clinically and biochemically. All study participants underwent genetic analysis to exclude involvement of the CLCN5 gene.

RESULTS

Evaluation of the 3 affected children showed glycosuria, generalized aminoaciduria, hypouricemia, uricosuria, low molecular weight (LMW) proteinuria, and hypercalciuria in all 3 children and phosphaturia in 2 children. They had no metabolic acidosis or renal insufficiency. One affected girl had nephrocalcinosis. Two children had a history of growth retardation and radiological findings of metabolic bone disease. Parathyroid hormone and 1,25-dihydroxyvitamin D [1,25(OH)2Vit D] blood levels in affected children were normal. Unaffected family members examined had no renal tubular defects or LMW proteinuria. Genetic linkage analysis excluded cosegregation of the ARPTH phenotype with the CLCN5 locus.

CONCLUSION

ARPTH is a new syndrome characterized by nonacidotic proximal tubulopathy, hypercalciuria, metabolic bone disease, and growth retardation. It can be distinguished from XLHN by its autosomal recessive mode of inheritance and normal serum levels of calciotropic hormones, as well as the absence of LMW proteinuria in obligate carriers. The gene mutated in ARPTH remains to be identified.