Levamisole Modulation of Podocytes' Actin Cytoskeleton in Nephrotic Syndrome

Podocytes play a central role in glomerular diseases such as (idiopathic) nephrotic syndrome (iNS). Glucocorticoids are the gold standard therapy for iNS. Nevertheless, frequent relapses are common. In children with iNS, steroid-sparing agents are used to avoid prolonged steroid use and reduce steroid toxicity. Levamisole is one of these steroid-sparing drugs and although clinical effectiveness has been demonstrated, the molecular mechanisms of how levamisole exerts its beneficial effects remains poorly studied. Apart from immunomodulatory capacities, nonimmunological effects of levamisole on podocytes have also been suggested. We aimed to elaborate on the effects of levamisole on human podocytes in iNS. RNA sequencing data from a human podocyte cell line treated with levamisole showed that levamisole modulates the expression of various genes involved in actin cytoskeleton stabilization and remodeling. Functional experiments showed that podocytes exposed to puromycin aminonucleoside (PAN), lipopolysaccharides (LPS), and NS patient plasma resulted in significant actin cytoskeleton derangement, reduced cell motility, and impaired cellular adhesion when compared to controls, effects that could be restored by levamisole. Mechanistic studies revealed that levamisole exerts its beneficial effects on podocytes by signaling through the glucocorticoid receptor and by regulating the activity of Rho GTPases. In summary, our data show that levamisole exerts beneficial effects on podocytes by stabilizing the actin cytoskeleton in a glucocorticoid receptor-dependent manner.

Multi-population genome-wide association study implicates immune and non-immune factors in pediatric steroid-sensitive nephrotic syndrome

Pediatric steroid-sensitive nephrotic syndrome (pSSNS) is the most common childhood glomerular disease. Previous genome-wide association studies (GWAS) identified a risk locus in the HLA Class II region and three additional independent risk loci. But the genetic architecture of pSSNS, and its genetically driven pathobiology, is largely unknown. Here, we conduct a multi-population GWAS meta-analysis in 38,463 participants (2440 cases). We then conduct conditional analyses and population specific GWAS. We discover twelve significant associations-eight from the multi-population meta-analysis (four novel), two from the multi-population conditional analysis (one novel), and two additional novel loci from the European meta-analysis. Fine-mapping implicates specific amino acid haplotypes in HLA-DQA1 and HLA-DQB1 driving the HLA Class II risk locus. Non-HLA loci colocalize with eQTLs of monocytes and numerous T-cell subsets in independent datasets. Colocalization with kidney eQTLs is lacking but overlap with kidney cell open chromatin suggests an uncharacterized disease mechanism in kidney cells. A polygenic risk score (PRS) associates with earlier disease onset. Altogether, these discoveries expand our knowledge of pSSNS genetic architecture across populations and provide cell-specific insights into its molecular drivers. Evaluating these associations in additional cohorts will refine our understanding of population specificity, heterogeneity, and clinical and molecular associations.

Uncovering risk factors for kidney injury in children with a solitary functioning kidney

Children with a solitary functioning kidney (SFK) have an increased risk of kidney injury. The exact risk of and risk factors for kidney injury remain unknown, which impedes personalized care. Here, we recruited a nationwide multicenter cohort of 944 patients with SFK to get more insight into this by consenting patients born in 1993-2020 and diagnosed with congenital or acquired SFK before adulthood. The median follow-up was 12.8 years and four indications of kidney injury were studied: urine protein-creatinine ratios, blood pressure, estimated glomerular filtration rate and use of anti-hypertensive/proteinuric medication. For each indicator except medication use, separate cut-off values for any injury and severe injury were used. Survival analyses indicated that at 18 years of age, any or severe kidney injury were present in 75% and 39% of patients with congenital SFK, respectively. Risk factors for kidney injury included kidney agenesis as cause of the SFK, anomalies in the SFK, and high body mass index at last follow-up. Kidney agenesis and being overweight were specifically associated with proteinuria and high blood pressure, whereas anomalies in the SFK were associated with reduced estimated glomerular filtration rates. The high prevalence of kidney injury in patients with SFK emphasizes the need for long-term follow-up, in which lifestyle is an important topic to address. More research into the etiological role of risk factors will help to translate our findings into individualized care strategies. Thus, our study shows that a significant proportion of children with SFK will develop kidney injury over time.

Identification and characterization of circulating immune complexes in IgA nephropathy

The underlying pathology of immunoglobulin A (IgA) nephropathy (IgAN), the most common glomerulonephritis worldwide, is driven by the deposition of immune complexes containing galactose-deficient IgA1 [Tn(+)IgA1] in the glomerular mesangium. Here, we report that novel anti-Tn circulating immune complexes (anti-Tn CICs) contain predominantly IgM, representing large macromolecular complexes of ~1.2 megadaltons to several megadalton sizes together with Tn(+)IgA1 and some IgG. These complexes are significantly elevated in sera of patients with IgAN, which contains higher levels of complement C3, compared to healthy individuals. Anti-Tn CICs are bioactive and induce specific proliferation of human renal mesangial cells. We found that these anti-Tn CICs can be dissociated with small glycomimetic compounds, which mimic the Tn antigen of Tn(+)IgA1, releasing IgA1 from anti-Tn CICs. This glycomimetic compound can also significantly inhibit the proliferative activity of anti-Tn CICs of patients with IgAN. These findings could enhance both the diagnosis of IgAN and its treatment, as specific drug treatments are now unavailable.

Clinical Management of Children with a Congenital Solitary Functioning Kidney: Overview and Recommendations

CONTEXT

A congenital solitary functioning kidney (cSFK) is a common developmental defect that predisposes to hypertension and chronic kidney disease (CKD) as a consequence of hyperfiltration. Every urologist takes care of patients with a cSFK, since some will need lifelong urological care or will come with clinical problems or questions to an adult urologist later in life.

OBJECTIVE

We aim to provide clear recommendations for the initial clinical management and follow-up of children with a cSFK.

EVIDENCE ACQUISITION

PubMed and EMBASE were searched to identify relevant publications, which were combined with guidelines on related topics and expert opinion.

EVIDENCE SYNTHESIS

Initially, cSFK diagnosis should be confirmed and risk factors for kidney injury should be identified using ultrasound. Although more research into early predictors of kidney injury is needed, additional congenital anomalies of the kidney or urinary tract and absence of compensatory kidney hypertrophy have repeatedly been associated with a worse prognosis. The role of voiding cystourethrography and antibiotic prophylaxis remains controversial, and is complicated by the exclusion of children with a cSFK from studies. A yearly follow-up for signs of kidney injury is recommended for children with a cSFK. As masked hypertension is prevalent, annual ambulatory blood pressure measurement should be considered. During puberty, an increasing incidence of kidney injury is seen, indicating that long-term follow-up is necessary. If signs of kidney injury are present, angiotensin converting enzyme inhibitors are the first-line drugs of choice.

CONCLUSIONS

This overview points to the urological and medical clinical aspects and long-term care guidance for children with a cSFK, who are at risk of hypertension and CKD. Monitoring for signs of kidney injury is therefore recommended throughout life. Large, prospective studies with long-term follow-up of clearly defined cohorts are still needed to facilitate more risk-based and individualized clinical management.

PATIENT SUMMARY

Many children are born with only one functioning kidney, which could lead to kidney injury later in life. Therefore, a kidney ultrasound is made soon after birth, and other investigations may be needed as well. Urologists taking care of patients with a solitary functioning kidney should realize the long-term clinical aspects, which might need medical management.

Concordance between creatinine- and cystatin C-based eGFR in clinical practice

The mean of GFR-estimates based on serum creatinine (eGFR_crea) and cystatin C (eGFR_cys) has superior accuracy than each estimate alone. Recent studies have shown that agreement between eGFR_crea and eGFR_cys is an indicator for the accuracy of the mean of the two estimates. As long as the difference between the two (|ΔeGFR|) is below 40%, a high P₃₀ accuracy rate of more than 90% was documented in research settings using gold-standard GFR measurements. This was the case in approximately 80% of the measurements. The study was set out to explore |ΔeGFR| in a broader pediatric nephrological population and identify factors influencing the discrepancy between eGFR_crea and eGFR_cys. We retrospectively analyzed 1596 simultaneous cystatin C and creatinine measurements in 649 unique patients at the pediatric nephrology outpatient clinic of VU university medical center. The FASage equation was used to calculate eGFR_crea, FAScys for eGFR_cys. |ΔeGFR| was calculated as 100x(|eGFR_crea-eGFR_cys|)/(0.5x(eGFR_crea+eGFR_cys). ΔeGFR below 40% was considered high agreement. Patient characteristics like age, diagnosis, glucocorticosteroid use, eGFR, BMI and sex were analyzed for their effect on ΔeGFR below or above 40% using non-parametric tests and a potential explanation for measurements with low agreement was sought. Eighty-seven percent of the population had a |ΔeGFR| lower than 40%. Measurements with |ΔeGFR| above 40% were significantly more frequent from patients with neural tube defects. In 102 out of 208 measurements with low agreement, a potential explanation was found. In a broad pediatric nephrological population, |ΔeGFR| is below 40% in the vast majority of measurements. In this group, the mean of eGFR_crea and eGFR_cys can be used as an accurate estimate of GFR.

Practice variations in the management of childhood nephrotic syndrome in the Netherlands

Nephrotic syndrome in childhood is a common entity in the field of pediatric nephrology. The optimal treatment of children with nephrotic syndrome is often debated. Previously conducted studies have shown significant variability in nephrotic syndrome management, especially in the choice of steroid-sparing drugs. In the Netherlands, a practice guideline on the management of childhood nephrotic syndrome has been available since 2010. The aim of this study was to identify practice variations and opportunities to improve clinical practice of childhood nephrotic syndrome in the Netherlands. A digital structured survey among Dutch pediatricians and pediatric nephrologists was performed, including questions regarding the initial treatment, relapse treatment, kidney biopsy, additional immunosuppressive treatment, and supportive care. Among the 51 responses, uniformity was seen in the management of a first presentation and first relapse. Wide variation was found in the tapering of steroids after alternate day dosing. Most pediatricians and pediatric nephrologists (83%) would perform a kidney biopsy in case of steroid-resistant nephrotic syndrome, whereas for frequent relapsing and steroid-dependent nephrotic syndrome this was 22% and 41%, respectively. Variation was reported in the steroid-sparing treatment. Finally, significant differences were present in the supportive treatment of nephrotic syndrome.Conclusion: Substantial variation was present in the management of nephrotic syndrome in the Netherlands. Differences were identified in steroid tapering, use of steroid coverage during stress, choice of steroid-sparing agents, and biopsy practice. To promote guideline adherence and reduce practice variation, factors driving this variation should be assessed and resolved. What is Known: • National and international guidelines are available to guide the management of childhood nephrotic syndrome. • Several aspects of the management of childhood nephrotic syndrome, including the choice of steroid-sparing drugs and biopsy practice, are controversial and often debated among physicians. What is New: • Significant practice variation is present in the management of childhood nephrotic syndrome in the Netherlands, especially in the treatment of FRNS, SDNS, and SRNS. • The recommendation on the steroid treatment of a first episode of nephrotic syndrome in the KDIGO guideline leaves room for interpretation and is likely the cause of substantial differences in steroid-tapering practices among Dutch pediatricians and pediatric nephrologists.

Prevention of relapses with levamisole as adjuvant therapy in children with a first episode of idiopathic nephrotic syndrome: study protocol for a double blind, randomised placebo-controlled trial (the LEARNS study)

INTRODUCTION

Idiopathic nephrotic syndrome (INS) is characterised by a high relapse rate up to 80% after initial response to standard therapy with corticosteroids. Steroid toxicity is common and causes a great burden of disease that negatively influences the health-related quality of life (HRQoL). Recently, studies have shown that levamisole, an anthelminthic drug, significantly improves relapse-free survival in children with frequent relapses or steroid dependency. Compared with other steroid-sparing drugs, levamisole has relatively few side effects. We hypothesise that adding levamisole to standard therapy with corticosteroids in children with a first episode of INS will prevent relapses, decrease cumulative dosage of steroids used and improve HRQoL. This paper presents the study protocol for the LEARNS study (LEvamisole as Adjuvant therapy to Reduce relapses of Nephrotic Syndrome).

METHODS AND ANALYSIS

An international, double-blind, placebo-controlled randomised trial will be conducted in 20 participating hospitals in the Netherlands and Belgium. Participants (n=92) with a first episode of INS, aged 2-16 years, who achieve remission after 4 weeks of oral prednisolone will be randomly assigned (1:1) to receive either levamisole 2.5 mg/kg alternate day or placebo added to prednisolone (18-week tapering schedule) for a total of 24 weeks. Follow-up will be until 2 years after first presentation. Additionally, parents and/or children will fill out five HRQoL questionnaires. Primary outcome of the LEARNS study is occurrence of relapses within 12 months after first presentation. Secondary outcomes include time to first relapse, cumulative steroid dose after 2 years, safety parameters and quality of life scores.

ETHICS AND DISSEMINATION

The trial was approved by the Medical Ethical Committee. Results of the study will be published in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NL6826, 2017-001025-41.

Author Correction: The copy number variation landscape of congenital anomalies of the kidney and urinary tract

In the version of this article initially published, affiliation 38 incorrectly read "ICNU-Nephrology and Urology Department, Barcelona, Spain"; "Renal Division, Hospital Clinic, IDIBAPS, University of Barcelona, Barcelona, Spain" is the correct affiliation. The error has been corrected in the HTML and PDF versions of the article.

The copy number variation landscape of congenital anomalies of the kidney and urinary tract

Congenital anomalies of the kidney and urinary tract (CAKUT) are a major cause of pediatric kidney failure. We performed a genome-wide analysis of copy number variants (CNVs) in 2,824 cases and 21,498 controls. Affected individuals carried a significant burden of rare exonic (i.e. affecting coding regions) CNVs and were enriched for known genomic disorders (GD). Kidney anomaly (KA) cases were most enriched for exonic CNVs, encompassing GD-CNVs and novel deletions; obstructive uropathy (OU) had a lower CNV burden and an intermediate prevalence of GD-CNVs; vesicoureteral reflux (VUR) had the fewest GD-CNVs but was enriched for novel exonic CNVs, particularly duplications. Six loci (1q21, 4p16.1-p16.3, 16p11.2, 16p13.11, 17q12, and 22q11.2) accounted for 65% of patients with GD-CNVs. Deletions at 17q12, 4p16.1-p16.3, and 22q11.2 were specific for KA; the 16p11.2 locus showed extensive pleiotropy. Using a multidisciplinary approach, we identified TBX6 as a driver for the CAKUT subphenotypes in the 16p11.2 microdeletion syndrome.

Combining GFR estimates from cystatin C and creatinine-what is the optimal mix?

BACKGROUND

Combining estimated glomerular filtration rate (eGFR) equations based on creatinine and cystatin C has been shown to improve the accuracy of GFR estimation. This study aims to optimize this strategy for height-independent GFR estimation in children.

METHODS

Retrospective study of 408 inulin clearance tests with simultaneous International Federation of Clinical Chemistry-calibrated measurements of creatinine, cystatin C, and urea in children (mean age 12.5 years, GFR 91.2 ml/min/1.73m²) comparing the arithmetic (mean_arith) and geometric means (mean_geom) of a height-independent creatinine-based (full age spectrum, based on age (FASage)) and a cystatin C-based equation (FAScys), with the complex height-dependent CKiD3 equation incorporating gender, height, cystatin C, creatinine, and urea.

RESULTS

Mean_geom had a P₃₀ accuracy of 89.2% compared to mean_arith 87.7% (p = 0.030) as well as lower bias and %precision error and performed almost as well as CKiD3 (P₃₀ accuracy 90.9%). Modifying the weight of FASage and FAScys when calculating the means showed that an equal contribution was most accurate in most patients. In spina bifida patients, FAScys alone outperformed any combination. Malignancy or nephritis patients had slightly higher accuracy with weighted means favoring cystatin C or creatinine, respectively. Disagreement between FAScys and FASage was inversely correlated with the accuracy of mean_geom. When disagreement exceeded 40%, application of weighted means based on diagnosis improved the performance of eGFR.

CONCLUSIONS

In the absence of height data, the optimal strategy for estimating GFR in children is by using the geometric mean of FASage and FAScys. When there is large disagreement between the two, weighted means based on diagnosis improve accuracy.

Estimation of GFR in children using rescaled beta-trace protein

INTRODUCTION

Beta-trace protein (BTP) is a low molecular weight protein, produced mainly in the cerebrospinal fluid. It has been proposed as a marker for kidney function. Recently, a new method for GFR estimation using mean normal values to rescale GFR marker concentrations has been described for creatinine and cystatin C, two commonly used endogenous markers for kidney function. The aim of this study is to apply this approach to BTP in children.

METHOD

We retrospectively analyzed serum concentrations of creatinine, cystatin C and BTP measured during inulin clearance tests in children. BTP was measured using a particle-enhanced immunonephelometric assay (Siemens Healthcare). A novel BTP-based eGFR equation was developed using published normal values for children: eGFR_BTP[ml/min/1.73m²] = 107.3/BTP/Q_BTP with Q_BTP = 0.69. Performance of this equation was compared to the established creatinine-based full age spectrum equation FASage and the cystatin C-based FAScys equations as well as the BTP-based Benlamri equation in terms of bias, % prediction error and P₃₀ and P₁₀ accuracy rates.

RESULTS

322 inulin clearance tests were studied. Overall, our novel equation performed comparably to the creatinine-based FASage and the BTP-based Benlamri equations but was less accurate than FAScys (P₃₀: 79.2 vs 86.3%, p = .008). Combining markers significantly enhanced performance compared to the single marker equations, with the exception of FAScys.

CONCLUSION

Rescaled BTP concentrations are a simple method for estimating GFR in children. However, the additional value of BTP for the estimation of GFR compared to rescaled creatinine and cystatin C still remains to be demonstrated.

Exome-wide Association Study Identifies GREB1L Mutations in Congenital Kidney Malformations

Renal agenesis and hypodysplasia (RHD) are major causes of pediatric chronic kidney disease and are highly genetically heterogeneous. We conducted whole-exome sequencing in 202 case subjects with RHD and identified diagnostic mutations in genes known to be associated with RHD in 7/202 case subjects. In an additional affected individual with RHD and a congenital heart defect, we found a homozygous loss-of-function (LOF) variant in SLIT3, recapitulating phenotypes reported with Slit3 inactivation in the mouse. To identify genes associated with RHD, we performed an exome-wide association study with 195 unresolved case subjects and 6,905 control subjects. The top signal resided in GREB1L, a gene implicated previously in Hoxb1 and Shha signaling in zebrafish. The significance of the association, which was p = 2.0 × 10^-5 for novel LOF, increased to p = 4.1 × 10^-6 for LOF and deleterious missense variants combined, and augmented further after accounting for segregation and de novo inheritance of rare variants (joint p = 2.3 × 10^-7). Finally, CRISPR/Cas9 disruption or knockdown of greb1l in zebrafish caused specific pronephric defects, which were rescued by wild-type human GREB1L mRNA, but not mRNA containing alleles identified in case subjects. Together, our study provides insight into the genetic landscape of kidney malformations in humans, presents multiple candidates, and identifies SLIT3 and GREB1L as genes implicated in the pathogenesis of RHD.

Proteinuria in Dent disease: a review of the literature

BACKGROUND

Dent disease is a rare X-linked recessive proximal tubulopathy caused by mutations in CLCN5 (Dent-1) or OCRL (Dent-2). As a rule, total protein excretion (TPE) is low in tubular proteinuria compared with glomerular disease. Several authors have reported nephrotic-range proteinuria (NP) and glomerulosclerosis in Dent disease. Therefore, we aimed to analyze protein excretion in patients with documented CLCN5 or OCRL mutations in a systematic literature review.

DESIGN

PubMed and Embase were searched for cases with documented CLCN5 or OCRL mutations and (semi-)quantitative data on protein excretion. The most reliable data (i.e., TPE > protein-creatinine ratio > Albustix) was used for NP classification.

RESULTS

Data were available on 148 patients from 47 reports: 126 had a CLCN5 and 22 an OCRLmutation. TPE was not significantly different between both forms (p = 0.11). Fifty-five of 126 (43.7 %) Dent-1 vs 13/22 (59.1 %) Dent-2 patients met the definition of NP (p = 0.25). Serum albumin was normal in all reported cases (24/148). Glomerulosclerosis was noted in 20/32 kidney biopsies and was strongly related to tubulointerstitial fibrosis, but not to kidney function or proteinuria.

CONCLUSION

More than half of the patients with both forms of Dent disease have NP, and the presence of low molecular weight proteinuria in a patient with NP in the absence of edema and hypoalbuminemia should prompt genetic testing. Even with normal renal function, glomerulosclerosis and tubulointerstitial fibrosis are present in Dent disease. The role of proteinuria in the course of the disease needs to be examined further in longitudinal studies.

Accurate eGFR reporting for children without anthropometric data

INTRODUCTION

Reporting estimated glomerular filtration rate (eGFR) instead of serum concentrations is advised in current guidelines. Most creatinine-based eGFR equations for children require height, a parameter not readily available to laboratories. Combining height-dependent creatinine- and cystatin C-based eGFR improves performance. Recently, a height-independent creatinine-based eGFR equation has been developed.

AIM

To compare the combination of height-independent creatinine- and cystatin C-based equations with a combination of equations using anthropometric data.

METHODS

Retrospective analysis of 408 pediatric inulin clearance studies with simultaneous height, creatinine, cystatin C and urea measurements. eGFR calculation using the recalibrated Schwartz_crea (height-dependent), FASage (height-independent) and the Schwartz_cys equation. The means (Schwartz_crea+Schwartz_cys)/2 and (FASage+Schwartz_cys)/2 were compared with the CKiD3 equation incorporating cystatin C, creatinine, urea, height and gender in terms of %prediction error and accuracy.

RESULTS

All three single parameter equations performed similarly (P₃₀ accuracy around 80%). (FASage+Schwartz_cys)/2 (P₃₀ 89.2%) and (Schwartz_crea+Schwartz_cys)/2 (P₃₀ 89.0%), performed comparably to CKiD3 (P₃₀ 90.0%). If the difference between the creatinine- and the cystatine C based eGFR was <40%, P₃₀ accuracy of the mean exceeded 90%.

CONCLUSION

Combining the height-independent FASage and Schwartz_Cys equations substantially improves accuracy and performs comparably to height-dependent equations. This allows laboratories to directly report eGFR in children.

Interpretation of the Fractional Excretion of Sodium in the Absence of Acute Kidney Injury: A Cross-Sectional Study

BACKGROUND/AIMS

The fractional excretion of sodium (FeNa) may be helpful in establishing the cause of acute renal failure. This study was performed to determine the influence of the glomerular filtration rate (GFR), sodium intake, and tubular function on FeNa in children without renal failure.

METHODS

In this single institute cross-sectional study, 24-h-urine collections from patients (4-18 years of age, GFR >60 mL/min/1.73 m2) were used when considered reliable, and analyzed to determine sodium excretion, creatinine clearance and FeNa. The influence of tubular function was studied in 5 patients with generalized tubular dysfunction.

RESULTS

Based on data from 761 patients, a multiple regression formula was designed based on GFR and sodium excretion that predicted over 80% of the variation in FeNa (R2 = 0.824, p < 0.001). Using this formula, the predicted FeNa was significantly lower than the measured FeNa in the children with tubular dysfunction.

CONCLUSION

FeNa depends on GFR and sodium intake, and tubular function cannot be assessed without possessing adequate knowledge on all factors. Therefore, no normal range or cut-off value for FeNa to assess tubular function can be given, and doing so is a misapplication of this equation.

Genetic Drivers of Kidney Defects in the DiGeorge Syndrome

BACKGROUND

The DiGeorge syndrome, the most common of the microdeletion syndromes, affects multiple organs, including the heart, the nervous system, and the kidney. It is caused by deletions on chromosome 22q11.2; the genetic driver of the kidney defects is unknown.

METHODS

We conducted a genomewide search for structural variants in two cohorts: 2080 patients with congenital kidney and urinary tract anomalies and 22,094 controls. We performed exome and targeted resequencing in samples obtained from 586 additional patients with congenital kidney anomalies. We also carried out functional studies using zebrafish and mice.

RESULTS

We identified heterozygous deletions of 22q11.2 in 1.1% of the patients with congenital kidney anomalies and in 0.01% of population controls (odds ratio, 81.5; P=4.5×10^-14). We localized the main drivers of renal disease in the DiGeorge syndrome to a 370-kb region containing nine genes. In zebrafish embryos, an induced loss of function in snap29, aifm3, and crkl resulted in renal defects; the loss of crkl alone was sufficient to induce defects. Five of 586 patients with congenital urinary anomalies had newly identified, heterozygous protein-altering variants, including a premature termination codon, in CRKL. The inactivation of Crkl in the mouse model induced developmental defects similar to those observed in patients with congenital urinary anomalies.

CONCLUSIONS

We identified a recurrent 370-kb deletion at the 22q11.2 locus as a driver of kidney defects in the DiGeorge syndrome and in sporadic congenital kidney and urinary tract anomalies. Of the nine genes at this locus, SNAP29, AIFM3, and CRKL appear to be critical to the phenotype, with haploinsufficiency of CRKL emerging as the main genetic driver. (Funded by the National Institutes of Health and others.).

Serological and genetic complement alterations in infection-induced and complement-mediated hemolytic uremic syndrome

BACKGROUND

The role of complement in the atypical form of hemolytic uremic syndrome (aHUS) has been investigated extensively in recent years. As the HUS-associated bacteria Shiga-toxin-producing Escherichia coli (STEC) can evade the complement system, we hypothesized that complement dysregulation is also important in infection-induced HUS.

METHODS

Serological profiles (C3, FH, FI, AP activity, C3d, C3bBbP, C3b/c, TCC, αFH) and genetic profiles (CFH, CFI, CD46, CFB, C3) of the alternative complement pathway were prospectively determined in the acute and convalescent phase of disease in children newly diagnosed with STEC-HUS or aHUS. Serological profiles were compared with those of 90 age-matched controls.

RESULTS

Thirty-seven patients were studied (26 STEC-HUS, 11 aHUS). In 39 % of them, including 28 % of STEC-HUS patients, we identified a genetic and/or acquired complement abnormality. In all patient groups, the levels of investigated alternative pathway (AP) activation markers were elevated in the acute phase and normalized in remission. The levels were significantly higher in aHUS than in STEC-HUS patients.

CONCLUSIONS

In both infection-induced HUS and aHUS patients, complement is activated in the acute phase of the disease but not during remission. The C3d/C3 ratio displayed the best discrepancy between acute and convalescent phase and between STEC-HUS and aHUS and might therefore be used as a biomarker in disease diagnosis and monitoring. The presence of aberrations in the alternative complement pathway in STEC-HUS patients was remarkable, as well.

Long-term follow-up of blood pressure and glomerular filtration rate in patients with a solitary functioning kidney: a comparison between Wilms tumor survivors and nephrectomy for other reasons

BACKGROUND

Children with unilateral Wilms tumor (WT) treated with chemotherapy and/or radiotherapy and nephrectomy have excellent survival rates. A solitary functioning kidney (SFK) is associated with progressive renal injury. This study aims to investigate the additional effect of Wilms tumor treatment on renal function compared with children with an SFK for non-oncological reasons.

METHODS

A single-center retrospective cohort study on the renal injury markers of 79 survivors of unilateral WT was performed and compared with a matched group of children with an SFK for non-oncological reasons. Mean age at follow-up was 12.4 (SD 5.9) years.

RESULTS

During follow-up, mean estimated glomerular filtration rate (eGFR) and blood pressure z-scores remained stable at an acceptable level. However, in the group of 31 WT patients with a follow-up of 15 years, 23% showed signs of renal injury. This proportion was smaller than the 54% in a group of SFK patients based on non-oncological causes (p = 0.004).

CONCLUSIONS

A significant proportion of WT survivors develop renal injury during follow-up. Our data may be an underestimation of the true frequency of progressive renal injury, due to a lack of information on proteinuria. As with patients with a non-oncological SFK, long-term follow-up is essential to monitor WT survivors.

Copy number variation analysis identifies novel CAKUT candidate genes in children with a solitary functioning kidney

Copy number variations associate with different developmental phenotypes and represent a major cause of congenital anomalies of the kidney and urinary tract (CAKUT). Because rare pathogenic copy number variations are often large and contain multiple genes, identification of the underlying genetic drivers has proven to be difficult. Here we studied the role of rare copy number variations in 80 patients from the KIMONO-study cohort for which pathogenic mutations in three genes commonly implicated in CAKUT were excluded. In total, 13 known or novel genomic imbalances in 11 of 80 patients were absent or extremely rare in 23,362 population controls. To identify the most likely genetic drivers for the CAKUT phenotype underlying these rare copy number variations, we used a systematic in silico approach based on frequency in a large dataset of controls, annotation with publicly available databases for developmental diseases, tolerance and haploinsufficiency scores, and gene expression profile in the developing kidney and urinary tract. Five novel candidate genes for CAKUT were identified that showed specific expression in the human and mouse developing urinary tract. Among these genes, DLG1 and KIF12 are likely novel susceptibility genes for CAKUT in humans. Thus, there is a significant role of genomic imbalance in the determination of kidney developmental phenotypes. Additionally, we defined a systematic strategy to identify genetic drivers underlying rare copy number variations.

Clinical implications of the solitary functioning kidney

Congenital anomalies of the kidney and urinary tract are the major cause of ESRD in childhood. Children with a solitary functioning kidney form an important subgroup of congenital anomalies of the kidney and urinary tract patients, and a significant fraction of these children is at risk for progression to CKD. However, challenges remain in distinguishing patients with a high risk for disease progression from those patients without a high risk of disease progression. Although it is hypothesized that glomerular hyperfiltration in the lowered number of nephrons underlies the impaired renal prognosis in the solitary functioning kidney, the high proportion of ipsilateral congenital anomalies of the kidney and urinary tract in these patients may further influence clinical outcome. Pathogenic genetic and environmental factors in renal development have increasingly been identified and may play a crucial role in establishing a correct diagnosis and prognosis for these patients. With fetal ultrasound now enabling prenatal identification of individuals with a solitary functioning kidney, an early evaluation of risk factors for renal injury would allow for differentiation between patients with and without an increased risk for CKD. This review describes the underlying causes and consequences of the solitary functioning kidney from childhood together with its clinical implications. Finally, guidelines for follow-up of solitary functioning kidney patients are recommended.

Height-independent estimation of glomerular filtration rate in children: an alternative to the Schwartz equation

OBJECTIVE

To compare the diagnostic performance of 2 height-independent equations used to calculate estimated glomerular filtration rate (eGFR), those of Pottel (eGFR-Pottel) and the British Columbia Children's Hospital (BCCH) (eGFR-BCCH), with the commonly used Schwartz equation (eGFR-Schwartz).

STUDY DESIGN

We externally validated eGFR-Pottel and eGFR-BCCH in a well-characterized pediatric patient population (n = 152) and compared their diagnostic performance with that of eGFR-Schwartz using Bland-Altman analysis. All patients underwent glomerular filtration rate measurement using the gold standard single-injection inulin clearance method (GFR-inulin).

RESULTS

Median GFR-inulin was 92.0 mL/min/1.73 m² (IQR, 76.1-107.4 mL/min/1.73 m²). Compared with GFR-inulin, the mean bias for eGFR-Schwartz was -10.1 mL/min/1.73 m(2) (95% limits of agreement [LOA], -77.5 to 57.2 mL/min/1.73 m(2)), compared with -12.3 mL/min/1.73 m² (95% LOA, -72.6 to 47.9 mL/min/1.73 m(2)) for eGFR-Pottel and -22.1 mL/min/1.73 m² (95% LOA, -105.0 to 60.8 mL/min/1.73 m(2)) for eGFR-BCCH. eGFR-Pottel showed comparable accuracy to eGFR-Schwartz, with 77% and 76% of estimates within 30% of GFR-inulin, respectively. eGFR-BCCH was less accurate than eGFR-Schwartz (66% of estimates within 30% of GFR-inulin; P < .01).

CONCLUSION

The performance of eGFR-Pottel is superior to that of eGFR-BCCH and comparable with that of eGFR-Schwartz. eGFR-Pottel is a valid alternative to eGFR-Schwartz in children and could be reported by the laboratory if height data are not available.

ANKS6 is a central component of a nephronophthisis module linking NEK8 to INVS and NPHP3

Nephronophthisis (NPH) is an autosomal recessive cystic kidney disease that leads to renal failure in childhood or adolescence. Most NPHP gene products form molecular networks. We have identified ANKS6 as a new NPHP family member that connects NEK8 (NPHP9) to INVERSIN (INVS, NPHP2) and NPHP3 to form a distinct NPHP module. ANKS6 localizes to the proximal cilium and knockdown experiments in zebrafish and Xenopus confirmed a role in renal development. Genetic screening identified six families with ANKS6 mutations and NPH, including severe cardiovascular abnormalities, liver fibrosis and situs inversus. The oxygen sensor HIF1AN (FIH) hydroxylates ANKS6 and INVS, while knockdown of Hif1an in Xenopus resembled the loss of other NPHP proteins. HIF1AN altered the composition of the ANKS6/INVS/NPHP3 module. Network analyses, uncovering additional putative NPHP-associated genes, placed ANKS6 at the center of the NPHP module, explaining the overlapping disease manifestation caused by mutations of either ANKS6, NEK8, INVS or NPHP3.

Unilateral renal agenesis: a systematic review on associated anomalies and renal injury

BACKGROUND

Unilateral renal agenesis (URA) is associated with other congenital anomalies of the kidney and urinary tract (CAKUT) and extra-renal anomalies. However, the reported prevalences of these anomalies are highly variable. We estimated the prevalence of associated CAKUT and extra-renal anomalies in patients with URA. Furthermore, we determined the prevalence of renal injury in URA patients.

METHODS

We conducted a systematic review of English and non-English articles using PubMed and Embase.com. Included studies reported at least one of the following items: incidence of URA, gender, side of URA, prenatal diagnosis, performance of micturating cystourethrogram, associated CAKUT, urinary tract infection or extra-renal anomalies. Studies that described a mean/median glomerular filtration rate (GFR) and proportions of patients with hypertension, micro-albuminuria or a decreased GFR were also included.

RESULTS

Analyses were based on 43 included studies (total number of patients: 2684, 63% male). The general incidence of URA was 1 in ∼2000. Associated CAKUT were identified in 32% of patients, of which vesicoureteral reflux was most frequently identified (24% of patients). Extra-renal anomalies were found in 31% of patients. Hypertension could be identified in 16% of patients, whereas 21% of patients had micro-albuminuria. Ten per cent of patients had a GFR<60 mL/min/1.73 m2;.

CONCLUSIONS

These aggregate results provide insight in the prevalence of associated anomalies and renal injury in patients with URA. Our systematic review implicates that URA is not a harmless malformation by definition. Therefore, we emphasize the need for clinical follow-up in URA patients starting at birth.

Risk factors for renal injury in children with a solitary functioning kidney

OBJECTIVE

The hyperfiltration hypothesis implies that children with a solitary functioning kidney are at risk to develop hypertension, proteinuria, and chronic kidney disease. We sought to determine the presenting age of renal injury and identify risk factors for children with a solitary functioning kidney.

METHODS

We evaluated 407 patients for signs of renal injury, defined as hypertension, proteinuria, an impaired glomerular filtration rate, and/or the use of renoprotective medication. Patients were subdivided on the basis of type of solitary functioning kidney and the presence of ipsilateral congenital anomalies of the kidney and urinary tract (CAKUT). The development of renal injury was analyzed with Kaplan-Meier analysis. Risk factors were identified by using logistic regression models.

RESULTS

Renal injury was found in 37% of all children. Development of renal injury increased by presence of ipsilateral CAKUT (odds ratio [OR] 1.66; P = .04) and age (OR 1.09; P < .001). Renal length was inversely associated with the risk to develop renal injury (OR 0.91; P = .04). In all patients, the median time to renal injury was 14.8 years (95% confidence interval 13.7-16.0 years). This was significantly shortened for patients with ipsilateral CAKUT (12.8 years, 95% confidence interval 10.6-15.1 years).

CONCLUSIONS

Our study determines independent risk factors for renal injury in children with a solitary functioning kidney. Because many children develop renal injury, we emphasize the need for clinical follow-up in these patients starting at birth.

Precision of estimating equations for GFR in children with a solitary functioning kidney: the KIMONO study

BACKGROUND AND OBJECTIVE

Children with a solitary functioning kidney may develop CKD. Although widely used, equations to estimate GFR are not validated in these patients. This study sought to determine the precision of common estimating equations in the KIMONO (KIdney of MONofunctional Origin) cohort.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Two creatinine-based (estimated GFR [eGFR]-Schwartz, urinary creatinine clearance), two cystatin C-based (eGFR-Zappitelli1, eGFR-CKiD [Chronic Kidney Disease in Children] 1), and two cystatin C/creatinine-based (eGFR-Zappitelli2, eGFR-CKiD2) estimates were compared with the gold standard GFR measured by inulin single injection (GFR-inulin) in 77 children with a solitary functioning kidney (time span of assembly, 2005-2012). Included patients were 1.5-19.8 years of age. Kidney Disease Outcomes Quality Initiative (K/DOQI) classification was compared between GFR-inulin and eGFR methods to analyze misclassification by estimating equations.

RESULTS

The eGFR-CKiD2 equation performed best in children with a solitary functioning kidney (mean bias, -0.9 ml/min per 1.73 m(2); 95% and 54% of values within ±30% and ±10% of GFR-inulin, respectively). Mean bias for eGFR-Schwartz was 0.4 ml/min per 1.73 m(2), with 90% and 33% of values within ±30% and ±10% of GFR-inulin, respectively. For all estimates, misclassification in K/DOQI stage ranged from 22% (eGFR-Zappitelli1) to 44% (urinary creatinine clearance) of children.

CONCLUSIONS

Use of a combined serum cystatin C/creatinine-based equation (eGFR-CKiD2) is recommended to monitor renal function in children with a solitary functioning kidney. When cystatin C is not routinely available, eGFR-Schwartz should be used. Misclassification in K/DOQI-stage remains a caveat for all equations.

Atypical hemolytic uremic syndrome in children: complement mutations and clinical characteristics

BACKGROUND

Mutations in complement factor H (CFH), factor I (CFI), factor B (CFB), thrombomodulin (THBD), C3 and membrane cofactor protein (MCP), and autoantibodies against factor H (αFH) with or without a homozygous deletion in CFH-related protein 1 and 3 (∆CFHR1/3) predispose development of atypical hemolytic uremic syndrome (aHUS).

METHODS

Different mutations in genes encoding complement proteins in 45 pediatric aHUS patients were retrospectively linked with clinical features, treatment, and outcome.

RESULTS

In 47% of the study participants, potentially pathogenic genetic anomalies were found (5xCFH, 4xMCP, and 4xC3, 3xCFI, 2xCFB, 6xαFH, of which five had ∆CFHR1/3); four patients carried combined genetic defects or a mutation, together with αFH. In the majority (87%), disease onset was preceeded by a triggering event; in 25% of cases diarrhea was the presenting symptom. More than 50% had normal serum C3 levels at presentation. Relapses were seen in half of the patients, and there was renal graft failure in all except one case following transplant.

CONCLUSIONS

Performing adequate DNA analysis is essential for treatment and positive outcome in children with aHUS. The impact of intensive initial therapy and renal replacement therapy, as well as the high risk of recurrence of aHUS in renal transplant, warrants further understanding of the pathogenesis, which will lead to better treatment options.

A case of tubulointerstitial nephritis in a patient with an influenza H1N1 infection

BACKGROUND

Patients suffering from an H1N1 infection mainly suffer from respiratory symptoms but may also develop symptoms in other organ systems, such as the kidneys.

CASE-DIAGNOSIS/TREATMENT

A 4 ½ year-old boy was admitted with relatively mild respiratory symptoms of H1N1 infection, but developed severe generalized proximal tubular dysfunction with sterile leucocyturia and a reversible rise in serum creatinine. He made a full recovery with supportive therapy.

CONCLUSION

Influenza H1N1 may be associated with acute tubulointerstitial nephritis.

Cystatin C more accurately detects mildly impaired renal function than creatinine in children receiving treatment for malignancy

BACKGROUND

Monitoring of renal function is crucial in pediatric oncology. The use of creatinine to estimate glomerular filtration rate (GFR) is hampered by its dependency on muscle mass. Muscle wasting is common in children with cancer, leading to overestimation of GFR. Data on cystatin C are sparse in pediatric oncology, although this marker could be particularly useful in this population.

PROCEDURE

Inulin clearance, estimated GFR using serum cystatin C according to Filler (eGFRcys) and serum creatinine according to Schwartz (eGFRcrea) were measured in 68 children with malignancy and 121 controls. We analyzed the difference between measured and estimated GFR and performance, bias and accuracy.

RESULTS

Multiple linear regression analysis showed overestimation of GFR by eGFRcrea in females (B = -21.18; P = 0.001), and in patients with malignancy (B = -21.77; P = 0.014). eGFRcys overestimated GFR in females (B = -10.47; P = 0.001), but was independent of treatment for malignancy. Agreement with gold standard in detecting GFR below 90 ml/min/1.73 m(2) is better for eGFRcys (AUC 0.854) than for eGFRcrea (AUC 0.675) in the group with cancer. They performed comparably in the control group. Bland-Altman analysis showed considerable bias for eGFRcrea compared to eGFRcys (-14.3 ml/min/1.73 m(2) vs. -7.3 ml/min/1.73 m(2)). The proportion of estimates within 30% of true GFR for eGFRcrea (72.1%) was lower than for eGFRcys (82.4%) in the group with cancer. In the control group eGFRcrea (84.3%) outperformed eGFRcys (76.0%). When using the 50% limits of agreement, eGFRcys outperformed eGFRcrea in both groups.

CONCLUSION

Cystatin C more accurately detects mildly impaired renal function than creatinine in children receiving treatment for malignancy.

Renal injury in children with a solitary functioning kidney--the KIMONO study

BACKGROUND

Children with a solitary functioning kidney (SFK) have an increased risk of developing hypertension, albuminuria and chronic kidney disease in later life. This renal injury is hypothesized to be caused by glomerular hyperfiltration that follows renal mass reduction in animal studies. Furthermore, children with an SFK show a high incidence of congenital anomalies of the kidney and urinary tract (CAKUT), which could further compromise renal function.

METHODS

A retrospective study of renal injury markers was performed in 206 children, divided into groups based on the origin of SFK [primary (congenital) SFK (n = 116) and secondary SFK (n = 90)]. Data on ipsilateral CAKUT were stratified separately. For blood pressure, albuminuria and glomerular filtration rate, longitudinal models were additionally developed using generalized estimated equation analysis.

RESULTS

Renal injury, defined as the presence of hypertension and/or albuminuria and/or the use of renoprotective medication, was present in 32% of all children with an SFK at a mean age of 9.5 (SD 5.6) years. Children with ipsilateral CAKUT had higher proportions of renal injury (48.3 versus 24.6%, P < 0.05). Furthermore, longitudinal models showed a decrease in glomerular filtration rate in both groups from the beginning of puberty onwards.

CONCLUSIONS

This large cohort study demonstrates that renal injury is present in children with an SFK at a young age, whereas our longitudinal models show an increased risk for chronic kidney disease in adulthood. Renal injury is even more pronounced in the presence of ipsilateral CAKUT. Therefore, we underline that clinical follow-up of all children with an SFK is needed.

Solid-phase synthesis of a pentavalent GalNAc-containing glycopeptide (Tn antigen) representing the nephropathy-associated IgA hinge region

Incomplete or aberrant glycosylation leading to Tn antigen (GalNAcalpha1-Ser/Thr) expression on human glycoproteins is strongly associated with human pathological conditions, including tumors, certain autoimmune diseases, such as the idiopathic IgA nephropathy, and may modulate immune homeostasis. In addition, the Tn antigen is highly expressed by certain pathogens and plays a role in host-pathogen interactions. To enable experimental approaches to study interactions of the Tn antigen with the immune system and analyze anti-Tn antibody responses in infection or disorders, we generated a Tn-expressing resource that can be used for high-throughput screening. In consideration of IgA nephropathy in which the hinge region is incompletely glycosylated, we used this hinge sequence that encodes five potential glycosylation sites as the ideal template for the synthesis of a Tn antigen-expressing glycopeptide. Inclusion of an N-terminal biotin in the peptide enabled binding to streptavidin-coated ELISA plates as monitored using Helix pomatia agglutinin or anti-Tn monoclonal antibody. We also found that the biotinylated IgA-Tn peptide is a functional acceptor for beta1-3-galactosylation using recombinant T-synthase (beta1-3-galactosyltransferase). Besides its immunochemical functionality as a possible diagnostic tool for IgA nephropathy, the peptide is an excellent substrate for glycan elongation and represents a novel template applicable for glycan-antigen-associated diseases.

Impact of gestational age and birth weight on amikacin clearance on day 1 of life

BACKGROUND AND OBJECTIVES

Intrauterine growth restriction (IUGR) and prematurity are associated with a low nephron endowment. It can therefore be expected that neonates who are born premature and/or after IUGR have a lower GFR. Measurement of GFR in neonates is difficult, but the clearance of amikacin has been proven to be a reliable marker. We hypothesized that amikacin clearance is lower after IUGR or premature birth as a marker of low nephron endowment.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Amikacin clearance was retrospectively analyzed in 161 neonates who received amikacin within the first 24 h of life. Using the MW/Pharm computer program, a population one-compartment model was calculated. The mean population pharmacokinetic parameters were individualized for each patient according to the maximum a posteriori Bayesian fitting method and provided the amikacin clearance.

RESULTS

Our results show that birth weight z score and gestational age are correlated with the clearance of amikacin (partial correlation coefficient 0.159, P = 0.046, and 0.396, P < 0.001, respectively), after correction for other factors.

CONCLUSIONS

We conclude that renal clearance on the first day of life is lower in neonates with a lower gestational age and/or birth weight z score. This indicates that both prematurity and IUGR impair GFR on the first day of life.

Unilateral multicystic dysplastic kidney: a meta-analysis of observational studies on the incidence, associated urinary tract malformations and the contralateral kidney

BACKGROUND

Many papers are published on cohorts with unilateral multicystic dysplastic kidney (MCDK) patients, but show variable results as to the incidence of associated urinary tract abnormalities. The objective of this study was to describe the status of the urinary tract, including contralateral hypertrophy and malformations, in patients with unilateral MCDK based on a meta-analysis of the literature, taking into account the timing of diagnosis (pre- versus postnatal) as a possible source of bias.

METHODS

A systematic review of the scientific literature in English was conducted using PubMed and Embase. A meta-analysis was performed with the studies that were identified using our reproducible search.

RESULTS

Based on analysis of the data in 19 populations, the overall incidence of unilateral MCDK is 1 in 4300 with an increasing trend over the years. A total of 67 cohorts with over 3500 patients with unilateral MCDK were included in the meta-analysis. Fifty-nine percent of patients were male and the MCDKs were significantly more often found on the left side (53.1%). Associated anomalies in the solitary functioning kidney were found in 1 in 3 patients, mainly vesicoureteric reflux (VUR, in 19.7%). In patients with VUR, 40% have severe contralateral VUR, defined as grade III-V. Contralateral hypertrophy, present in 77% of patients after a follow-up of at least 10 years, showed a trend to be less pronounced in patients with VUR. Timing of the diagnosis of MCDK did not essentially influence the results.

CONCLUSIONS

These aggregate results provide insight into the incidence, demographic data and associated anomalies in patients with unilateral MCDK. One in three patients with unilateral MCDK show anomalies in the contralateral, solitary functioning kidney. However, studies into the long-term consequences of these anomalies are scarce.

Pediatric acute kidney injury in the ICU: an independent evaluation of pRIFLE criteria

OBJECTIVE

The present study was undertaken to evaluate the practicability of the proposed pediatric RIFLE (pRIFLE) criteria in a patient population at risk for acute kidney injury (AKI) and to analyze the prevalence and association of AKI as defined by pRIFLE with mortality.

DESIGN

Retrospective, descriptive cohort study.

SETTING

Single-center, 9-bed PICU facility.

PATIENTS

Children with respiratory failure requiring mechanical ventilation for more than 4 days admitted between January 2002 and December 2006.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Data of 103 patients were studied. Median age was 4.5 years (range 1 month-17 years). Six patients received renal replacement therapy. Seventeen patients (17%) died. Sixty patients (58%) developed AKI by pRIFLE. Mean time to attainment of the first RIFLE stratum was 1.9 +/- 1.6 days. By pRIFLE, 34 of the 60 patients fulfilled the maximum AKI criteria on the first day after admission based on the estimated creatinine clearance criterion. Patients with AKI according to the pRIFLE scoring system had five times higher mortality than patients without AKI (25 vs. 5%, P < 0.05).

CONCLUSIONS

We observed a high incidence of significant AKI in a PICU population at risk, which was associated with high mortality. Pediatric RIFLE criteria may guide in the early identification of patients at risk for AKI and in the initiation of therapy.

Beta-trace protein is not superior to cystatin C for the estimation of GFR in patients receiving corticosteroids

OBJECTIVES

Comparison of the effect of corticosteroid therapy on the diagnostic performance of cystatin C (Cys) and beta-trace protein (bTP), two endogenous markers of GFR.

DESIGN AND METHODS

Out of a total of 193 pediatric inulin clearance studies, a random sample of 85 steroid-free studies served to establish GFR prediction equations (eGFR), which were used to compare the remaining 76 steroid-free and 32 steroid-positive studies (median prednisone dose 33.0 mg m(-2) day(-1)).

RESULTS

We found a positive relationship between prednisone dose and eGFR(betaTP) (b=0.414, p=0.0002) and a negative relationship with eGFR(cys) (b=-0.208, p=0.0091). Only Cys independently predicted GFR below 90 mL min(-1) 1.73 m(-2), both in steroid-positives (b=6.260, p=0.010) and steroid-negatives (b=6.845, p=0.012). Glucocorticoid therapy did not affect the accuracy in estimating GFR within 30% of measured GFR for Cys, while accuracy was lower with bTP (65.6% vs. 81.6%, p=0.08).

CONCLUSION

Glucocorticoids have less impact on the diagnostic accuracy of Cys than bTP.

Increased urinary cystatin C reflects structural and functional renal tubular impairment independent of glomerular filtration rate

OBJECTIVES

The ratio of the urinary mass concentrations of cystatin C and creatinine (UcysC/Ucrea)>/=11.3 mg/mmol has recently been proposed as an accurate marker for the detection of GFR</=60 mL/min/1.73 m(2).

DESIGN AND METHODS

We prospectively evaluated the diagnostic performance of UcysC/Ucrea>/=11.3 mg/mmol and factors associated with increased UcysC/Ucrea in 72 children and adults with a wide variety of renal disorders. UcysC/Ucrea was calculated, and GFR wad estimated from serum creatinine and cystatin C by equations.

RESULTS

UcysC/Ucrea>/=11.3 mg/mmol had a low diagnostic value to detect GFR values</=60 mL/min/1.73 m(2) estimated by creatinine or cystatin-C-based equations with sensitivities of 72% and 63%, and specificities of 42% and 34%. ROC curves for UcysC/Ucrea to detect GFR</=60 mL/min/1.73 m(2) confirmed this with AUCs of 0.59 for creatinine and 0.57 for cystatin-C-based equations. Multivariate analysis identified tubular proteinuria, tubulointerstitial disease and heavy proteinuria, but not GFR</=60 mL/min/1.73 m(2), as factors independently associated with increased UcysC/Ucrea.

CONCLUSIONS

UcysC/Ucrea>/=11.3 mg/mmol is not an accurate marker to detect GFR</=60 mL/min/1.73 m(2), but reflects tubular dysfunction and proteinuria due to heavy proteinuria and tubulointerstitial disease.

Novel OCRL1 mutations in patients with the phenotype of Dent disease

BACKGROUND

Dent disease is an X-linked tubulopathy frequently caused by mutations affecting the voltage-gated chloride channel and chloride/proton antiporter ClC-5. A recent study showed that defects in OCRL1, encoding a phosphatidylinositol 4,5-bisphosphate 5-phosphatase (Ocrl) and usually found mutated in patients with Lowe syndrome, also can provoke a Dent-like phenotype (Dent 2 disease).

METHODS

We investigated 20 CLCN5-negative males from 17 families with a phenotype resembling Dent disease for defects in OCRL1.

RESULTS

In our complete series of 35 families with a phenotype of Dent disease, a mutation in the OCRL1 gene was detected in 6 kindreds. All were novel frameshift (Q70RfsX88 and T121NfsX122, detected twice) or missense mutations (I257T and R476W). None of our patients had cognitive or behavioral impairment or cataracts, 2 classic hallmarks of Lowe syndrome. All patients had mild increases in lactate dehydrogenase and/or creatine kinase levels, which rarely is observed in CLCN5-positive patients, but frequently found in patients with Lowe syndrome. To explain the phenotypic heterogeneity caused by OCRL1 mutations, we performed extensive data-bank mining and extended reverse-transcriptase polymerase chain reaction analysis, which provided no evidence for yet unknown (tissue-specific) alternative OCRL1 transcripts.

CONCLUSION

Mutations in the OCRL1 gene are found in approximately 23% of kindreds with a Dent phenotype. Defective protein sorting/targeting of Ocrl might be the reason for mildly elevated creatine kinase and lactate dehydrogenase serum concentrations in these patients and a clue to suspect Dent disease unrelated to CLCN5 mutations. It remains to be elucidated why the various OCRL1 mutations found in patients with Dent 2 disease do not cause cataracts.

Postnatal food restriction in the rat as a model for a low nephron endowment

A low nephron endowment may be associated with hypertension. Nephrogenesis is the process that leads to the formation of nephrons until week 36 of gestation in humans and may be inhibited by many factors like intrauterine growth restriction and premature birth. To study the consequences of a low glomerular number, animal models have been developed. We describe a model of postnatal food restriction in the rat in which litter size is increased to 20 pups, which leads to growth restriction. In the rat, active nephrogenesis continues until postnatal day 8, which coincides with the growth restriction in our model. Design-based stereological methods were used to estimate glomerular number and volume. Our results show an ∼25% lower glomerular number in rats after postnatal food restriction (30,800 glomeruli/kidney) compared with control rats (39,600 glomeruli/kidney, P < 0.001). Mean glomerular volume was increased by 35% in the growth-restricted rats ( P = 0.006). There was a significant negative correlation between glomerular volume and glomerular number ( r = −0.76, P < 0.001). We conclude that postnatal food restriction in the rat leads to a low nephron endowment with compensatory enlargement. It is therefore a suitable model to study the effect of intrauterine growth restriction or prematurity on kidney development and the consequences of a reduced glomerular number in later life.

Intrauterine growth restriction increases blood pressure and central pulse pressure measured with telemetry in aging rats

OBJECTIVES

Intrauterine growth restriction (IUGR) is associated with a higher risk of hypertension in adulthood. In Western countries, IUGR is based on uteroplacental dysfunction. We hypothesize that aging augments the increased baseline blood pressure after IUGR and alters the cardiovascular response to acute stress.

METHODS

To evaluate blood pressure during aging in the rat, we used a model of uteroplacental dysfunction (bilateral uterine artery ligation). Blood pressure was measured in male offspring at the ages of 6, 9, and 12 months using telemetry, allowing for unstressed measurements in conscious animals. At 6 and 12 months of age, cardiovascular data were obtained during acute olfactory stress induced by ammonia and subsequent recovery.

RESULTS

Rats born after IUGR had lower birth weights (4.6 versus 6.5 g, P < 0.001) and did not completely catch up in weight by 12 months of age (519 versus 567 g, P < 0.01). Systolic blood pressure was significantly higher in IUGR animals at all ages. Pulse pressure (PP) was identical in both groups at the age of 6 months. However, PP increased in the IUGR group with increasing age, unlike the control group, and was significantly higher at 9 and 12 months of age. At the age of 12 months, there was a highly significant negative correlation between birth weight and PP (r = -0.82, P < 0.001). IUGR rats reached a higher peak in systolic blood pressure during stress, and showed a longer period for the raised heart rate to recover after stress.

CONCLUSIONS

IUGR is associated with raised baseline blood pressure, an increasing PP with age, and an altered stress response.

Association of birth weight with cardiovascular parameters in adult rats during baseline and stressed conditions

Low birth weight (LBW) due to intrauterine growth restriction (IUGR) in humans is associated with increased blood pressure (BP) in adulthood. In Western countries, IUGR is based on uteroplacental dysfunction. We used an animal model of uteroplacental dysfunction to evaluate this correlation. We hypothesize that IUGR increases baseline BP and alters the BP response to acute stress, which may explain BP differences in previous studies using stressful methods to obtain BP. IUGR was induced by bilateral uterine artery ligation in pregnant Wistar rats according to a modified method of Wigglesworth. BP was measured in the offspring using telemetry, allowing for unstressed measurements in conscious animals. Cardiovascular data were obtained at the age of 12 wk during baseline and acute olfactory stress induced by an ammonia gauze. Rats born after IUGR had a lower birth weight versus controls and did not completely catch up in weight. At baseline, systolic BP (SBP), mean arterial pressure (MAP), and pulse pressure (PP) were elevated in IUGR rats versus controls, by 8, 6, and 5 mm Hg, respectively. There was a strong negative correlation between birth weight and SBP and between birth weight and PP. During acute stress, there was a tendency to reach a higher peak in SBP and to need a longer period to recover in IUGR animals. We conclude that IUGR is associated with increased baseline BP.

R561C missense mutation in the SMARCAL1 gene associated with mild Schimke immuno-osseous dysplasia

Autosomal-recessive Schimke immuno-osseous dysplasia (SIOD) characterized by spondyloepiphyseal dysplasia, focal-segmental glomerulosclerosis (FSGS), T-cell immunodeficiency and facial dysmorphism is caused by defects in the SMARCAL1 gene. The gene product is involved in the transcriptional regulation of other genes. A 12-year-old boy of consanginous Turkish descent developed disproportionate short stature from spondyloepiphyseal dysplasia at the age of 6 and nephrotic syndrome at the age of 10 years. Renal biopsy revealed FSGS, the kidney function was normal, T-lymphocytes were diminished without infectious complications, and he has had no cerebral ischemia. Analysis of the patient's SMARCAL1 gene revealed a novel homozygous C1798T transition leading to a R561C substitution. The parents and two healthy sisters were found to be heterozygous. A younger brother, who is also homozygous for the mutation, is clinically asymptomatic and has no proteinuria at the age of 18 months. Still, his CD4 cells are diminished. For SMARCAL1 mutations a clear genotype-phenotype correlation has been reported: severe SIOD with in utero or early-childhood onset leading to end-stage renal disease within a few years is caused by nonsense, frame shift or splice mutations. Many patients die from infections and cerebrovascular insults during childhood. Mild SIOD manifests later and progresses more slowly without infectious or cerebral vascular complications--the underlying defect being missense mutations in all three patients reported so far. The novel R561C missense mutation in our patient with mild SIOD is additional evidence for the genotype-phenotype correlation reported for SMARCAL1 mutations.

Therapeutic total plasma exchange in a child with neuroblastoma-related anti-Hu syndrome

A 5-year-old boy underwent total plasma exchange to remove anti-neuronal anti-Hu autoantibodies as a complication of neuroblastoma, leading to autonomic bowel dysfunction. Total plasma exchange (TPE) resulted eventually in a reduction of autoantibody levels, but, more importantly, led to improvement of bowel function. TPE proved to be a safe and effective treatment option in neuroblastoma-related anti-Hu syndrome in a child.

Altered activity of plasma hemopexin in patients with minimal change disease in relapse

Since an active isoform of plasma hemopexin (Hx) has been proposed to be a potential effector molecule in minimal change disease (MCD), we tested plasma and urine samples from subjects with MCD in relapse (n = 18) or in remission (n = 23) (after treatment with prednisolone) for presence or activity of Hx. For comparison, plasma or urine from proteinuric subjects with focal and segmental glomerulosclerosis (FSGS, n = 11), membranoproliferative glomerulonephritis (MPGN, n = 9), IgA nephropathy (n = 5) or healthy control donors (n = 10), were incorporated into the study. Electrophoresis and Western blotting methods were used for evaluation of the Hx status, whereas protease activity of Hx was tested upon kidney tissue in vitro according to standard methods. The results show (1) a decreased mean titer of plasma Hx exclusively in MCD relapse subjects as compared with MCD in remission (0.21+/-0.14 mg/ml vs 0.44+/-0.06 mg/ml; p < 0.01). Mean Hx titers in other proteinuric subjects ranged from 0.38+/-0.05 mg/ml to 0.40+/- 0.06 mg/ml, whereas, the mean titer of healthy controls was 0.59+/-0.03 mg Hx/ml; (2) an increased Hx activity (expressed in arbitrary units) exclusively in plasma from MCD relapse subjects (3.3+/-0.72 vs 1.16+/-0.56, MCD remission; p < 0.01); (3) different Western blot patterns in MCD relapse vs remission plasma; (4) reduced stainability or virtual absence of the 80-kD Hx band in blots of urine from MCD relapse in contrast to urine samples from other proteinuric subjects with FSGS, MPGN, or IgA nephropathy. It is concluded that Hx in MCD relapse subjects may exist in an altered isoform, showing enhanced protease activity as compared with subjects in remission, subjects with other forms of primary glomerulopathy, or healthy control individuals.

Glomerular Number and Function Are Influenced by Spontaneous and Induced Low Birth Weight in Rats

A link exists between low birth weight and diseases in adulthood, such as hypertension, cardiovascular disease, and insulin resistance. Intrauterine growth restriction (IUGR) has been used to explain this association and has been shown to lead to a nephron endowment in humans. A reduction in glomerular number has been described in animal models with induced low birth weight as well but not in animals with spontaneous low birth weight. It therefore is debatable whether the models are suitable. The effect on glomerular number and size was studied in rats with naturally occurring IUGR and experimental IUGR, induced by bilateral uterine artery ligation. Design-based stereologic methods were used. Urinary protein excretion was determined as a measure of renal damage. Results showed a decrease of approximately 20% in glomerular number in both groups of IUGR (control 35,400, naturally occurring IUGR 30,900, and experimental IUGR 28,000 glomeruli per kidney). Mean glomerular volume was increased in both IUGR groups, which was associated with an increased proteinuria. It is concluded that IUGR leads to a nephron endowment with a compensatory glomerular enlargement. This compensation is associated with more proteinuria in the long run. Uterine artery ligation in the pregnant rat is a suitable model to study the effects of IUGR on the kidney.