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.

Metabolic alkalosis in infants treated with peritoneal dialysis

BACKGROUND

Acid-base balance is maintained by kidney excretion of titratable acids and bicarbonate reabsorption. Metabolic alkalosis is uncommon in dialysis-treated patients. The aim of this retrospective study was to assess the rate of metabolic alkalosis in pediatric patients treated with peritoneal dialysis.

METHODS

Medical records of children treated with peritoneal dialysis in Shaare Zedek Medical Center from January 2000 to June 2021 were reviewed and compared with young adults currently treated with peritoneal dialysis. Demographic, clinical, and peritoneal dialysis characteristics were extracted from the medical records.

RESULTS

Thirty chronic peritoneal dialysis patients were included in our study, seven under 2 years, 13 between 2 and 18 years, and 10 adults. 90.3% of the measurements in infants showed metabolic alkalosis compared to 32.3% in the 2-18-year group and none in the adult group. Higher size-adjusted daily exchange volume, lack of urine output, and high lactate-containing dialysate were associated with metabolic alkalosis. Alkalosis was not explained by vomiting, diuretic therapy, or carbonate-containing medications. High transport membrane, low dietary protein, and malnutrition, all previously reported explanations for metabolic alkalosis, were not found in our study.

CONCLUSIONS

Metabolic alkalosis is common in infants treated with peritoneal dialysis as opposed to older children and adults. High lactate-containing dialysate is a possible explanation. Higher size-adjusted daily dialysate exchange volume, which may reflect higher bicarbonate absorption, is another independent predictor of alkalosis. Acid-base status should be closely followed in infants, and using a dialysis solution with lower bicarbonate or lactate level should be considered. A higher resolution version of the graphical abstract is available as Supplementary Information.

[PEDIATRIC NEPHROLOGY IN THE TIME OF CORONA]

Symptomatic coronavirus 2019 (COVID-19) infection usually presents with upper airway symptoms, but may lead to complications, such as pneumonia and involvement of other organs, or even death. Children often have a mild clinical course or may be asymptomatic, however, a severe complication of multisystem inflammatory syndrome has been described in rare cases. In severe COVID-19 infection, acute kidney injury may manifest even in children without comorbidities. The aim of this review is to present available data on renal involvement in pediatric COVID-19, and disease manifestations in children with underlying chronic kidney disease (CKD) or children receiving immunosuppressive medications due to kidney transplantation or glomerular disease. Although it could be assumed that children with CKD, including immunosuppressed patients, might be a high risk group for infection and severity of COVID-19 disease, this is not supported by current available data.

COVID-19 in children and young adults with kidney disease: risk factors, clinical features and serological response

BACKGROUND

Chronic kidney disease (CKD) and kidney transplantation in adults are well-recognized risk factors for coronavirus disease 2019 (COVID-19) associated morbidity and mortality. Data on the toll of the pandemic on children and young adults with kidney disease is scarce. The aim of this study was to assess the incidence and severity of COVID-19, as well as the serological response, in this population.

METHODS

Study population included all patients with CKD stage 3-5, glomerular disease treated with immunosuppression and kidney transplant recipients followed-up at a tertiary medical center, between 1.12.2020 and 15.2.2021. Data collected included PCR testing, symptoms, exposure, and socio-demographic data. Anti-SARS-CoV-2 antibodies were tested.

RESULTS

A total of 197 children and 63 young adults were included, 57% were Jewish, 43% were Arab. PCR-confirmed COVID-19 incidence was 20.8%, 37% of cases were asymptomatic, three patients were hospitalized for observation, and the remainder had mild symptoms. Kidney function remained stable without treatment modification. Risk factors for infection included exposure at home (OR 15.4, 95% CI 6.9-34.2) and number of household members (OR 1.45, 95% CI 1.21-1.73). Anti-SARS-CoV-2 antibodies were detected in 61% of cases and were not associated with COVID-19 severity or immunosuppressive therapy. Three patients who did not develop antibodies had a mild recurrent infection.

CONCLUSIONS

Unlike COVID-19 in adult patients with kidney disease, in our cohort of children and young adults, COVID-19 incidence was similar to the general population and all cases were mild. It may be unnecessary to impose severe restrictions on this patient population during the pandemic.

Mutations in KIRREL1, a slit diaphragm component, cause steroid-resistant nephrotic syndrome

Steroid-resistant nephrotic syndrome is a frequent cause of chronic kidney disease almost inevitably progressing to end-stage renal disease. More than 58 monogenic causes of SRNS have been discovered and majority of known steroid-resistant nephrotic syndrome causing genes are predominantly expressed in glomerular podocytes, placing them at the center of disease pathogenesis. Herein, we describe two unrelated families with steroid-resistant nephrotic syndrome with homozygous mutations in the KIRREL1 gene. One mutation showed high frequency in the European population (minor allele frequency 0.0011) and this patient achieved complete remission following treatment, but later progressed to chronic kidney disease. We found that mutant KIRREL1 proteins failed to localize to the podocyte cell membrane, indicating defective trafficking and impaired podocytes function. Thus, the KIRREL1 gene product has an important role in modulating the integrity of the slit diaphragm and maintaining glomerular filtration function.

Early puberty in end stage renal failure and renal transplant recipients

Background Delayed puberty and hypogonadism are common in children with chronic kidney disease and in renal transplant recipients, but precocious puberty has rarely been reported in these populations. We describe six girls with precocious and/or early-onset, rapidly progressive puberty before and following renal transplantation. Methods Of 112 children under the age of 18 years (67 boys, 45 girls) who received renal transplants between 2010 and 2018, six girls presented with precocious or rapidly progressive early puberty at ages 6-7/12, 7-2/12, 7-4/12, 8, 8-8/12 and 8-11/12 years. Clinical evaluation included measurements of height, weight, body mass index (BMI), Tanner staging and bone age assessment. Gonadotropin responses to intravenous gonadotropin releasing hormone (GnRH) or intramuscular triptorelin acetate were determined. Results Tanner breast stage 3 was noted at 2-6 years following renal transplantation in five girls, four with preserved kidney function. One girl began puberty before renal transplantation. Peak luteinizing hormone (LH) and follicular stimulating hormone (FSH) levels were 6.5, 20.2, 7.83, 19.1, 9 and 2.2 mIU/mL and 13, 8.3, 8.01, 7.5, 8.1 and 7.7 mIU/mL, respectively. Treatment with an intramuscular slow-release formulation of triptorelin acetate every 4 weeks slowed progression of breast development. Conclusions Although delayed puberty is more common in children with renal disease, precocious puberty can also be seen. Evaluation of growth and puberty by a pediatric endocrinologist should be part of the routine care for all children following kidney transplantation.

Eosinophilia in a peritoneal dialysis patient: Answers

Icodextrin is a starch-derived glucose polymer used in peritoneal dialysis dialysate to treat volume overload by increasing ultrafiltration in patients with end-stage renal disease. Reported adverse reactions to icodextrin are mild and rare and mainly consist of skin rash that resolves spontaneously after discontinuation of treatment. We describe a young patient with extreme eosinophilia that appeared with the use of icodextrin, disappeared after its discontinuation, and reappeared after a rechallenge with the drug. The eosinophilia was not associated with peritonitis, was asymptomatic, and fully resolved after discontinuation of the drug. Severe eosinophilia can potentially cause tissue damage in several organs, which would indicate that blood eosinophil count is recommended in routine complete blood counts while icodextrin peritoneal dialysis is being administered.

Vitamin A deficiency associated with urinary retinol binding protein wasting in Dent's disease

BACKGROUND

Three patients with Dent's disease presented with complaints of impaired night vision or xerophthalmia and were found to have severely decreased serum retinol concentrations. Retinol, bound to its carrier retinol-binding protein (RBP), is filtered at the glomerulus and reabsorbed at the proximal tubule. We hypothesized that urinary loss of retinol-RBP complex is responsible for decreased serum retinol.

OBJECTIVE AND METHODS

The study aim was to investigate vitamin A status and RBP in serum and urine of patients with genetically confirmed Dent's disease.

RESULTS

Eight patients were studied, three boys had clinical vitamin A deficiency, three had asymptomatic deficiency, and two young men with Dent's disease and impaired renal function had normal retinol values. Serum RBP concentrations were low in patients with vitamin A deficiency and were correlated with vitamin A levels. Urinary RBP concentrations were increased in all patients (2,000-fold), regardless of vitamin A status. This was in contrast to patients with glomerular proteinuria who had only mildly increased urinary RBP with normal serum RBP and vitamin A, and patients with cystinosis with impaired renal function who had massive urinary RBP losses but without a decrease in serum RBP or vitamin A levels. Treatment with vitamin A supplements in patients with retinol deficiency resulted in rapid resolution of ocular symptoms and an increase in serum retinol concentrations.

CONCLUSIONS

Vitamin A deficiency is common in patients with Dent's disease and preserved renal function. We therefore recommend screening these patients for retinol deficiency and treating them before visual symptoms develop.

B-type natriuretic peptides are reliable markers of cardiac strain in CKD pediatric patients

Myocardial damage and strain are common in children with chronic renal failure. The most prevalent pathologies, as defined by echocardiography, are left ventricular hypertrophy (LVH), diastolic and systolic dysfunction, and altered LV geometry. Troponin I and T, as well as B-type natriuretic peptide (BNP) and its cleavage fragment NT-proBNP, are known to be good markers of myocardial damage and stress, respectively, in the general adult population and among those with chronic kidney disease (CKD). In this study we measured the levels of troponins I and T, BNP, and NT-proBNP in a group of children and young adults with CKD stages 3-5 and determined their respective correlations with echocardiographic and laboratory abnormalities. BNP and NT-proBNP levels and their log values correlated well with the following parameters: diastolic blood pressure, estimated glomerular filtration rate, time-averaged hemoglobin levels, and LV mass. Both BNP and NT-proBNP levels, but not those of either troponin, were found to be reliable surrogate markers of strained hearts, defined as having LVH or diastolic or systolic dysfunction, in the pediatric CKD stages 3-4 group. The log NT-proBNP value was also found to be a good marker of cardiac strain in the CKD stage 5 group of patients. Serum BNP and NT-proBNP threshold concentrations of 43 and 529 pg/ml, respectively, were found to have the best sensitivity and specificity in predicting strained hearts. Based on these findings, we conclude that both BNP and NT-proBNP levels, but not those of troponins I and T, can serve as inexpensive, simple, and reliable markers of stressed hearts in the pediatric CKD patient population.

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.

Dose of dialysis based on body surface area is markedly less in younger children than in older adolescents

BACKGROUND AND OBSERVATIONS: The current denominator for dosing dialysis is the urea distribution volume (V). Normalizing Kt/V to body surface area (S) has been proposed, but the implications of doing this in children have not been examined.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Dialysis dose given to children and adolescents was calculated in terms of conventional V-based scaling and surface-area-normalized standard Kt/V (SAN-stdKt/V) calculated as stdKt/V x (Vant/S)/17.5, where Vant was an anthropometric estimate of V calculated using the Morgenstern equation. Formal 2-pool modeling was used to compute all dialysis adequacy outputs.

RESULTS

In 34 children (11 girls, 23 boys) dialyzed 3 times a week, age range 1.4 to 18 years, the mean delivered equilibrated Kt/V (eKt/V) was 1.40, and the mean stdKt/V was 2.49, both of which tended to be higher in younger children. The ratio of Vant to S was 15.6 +/- 2.69 and was strongly associated with age between ages 2 and 16. SAN-stdKt/V averaged 2.21 and was strongly correlated with age between ages 2 and 16. If one considers a desired target for SAN-stdKt/V to be 2.45, all children less than 10 years of age were below target, despite having relatively high values of eKt/V and stdKt/V.

CONCLUSIONS

If a surface-area-based denominator were to be adopted for dialysis dosing, most children under 10 years of age would receive markedly less dialysis than adolescent patients and would require 6- to 8-hour hemodialysis sessions or, for the youngest children, treatments given more frequently than 3 times/wk.

A comprehensive study of cardiovascular risk factors, cardiac function and vascular disease in children with chronic renal failure

BACKGROUND

Cardiovascular disease causes major morbidity and is an important determinant of premature death in the paediatric chronic kidney disease (CKD) population. It is composed of three separate, although interrelated, disease processes: atherosclerosis, arteriosclerosis (i.e. medial vascular calcifications) and myocardial disease. Myocardial consequences of atherosclerosis barely exist in children, thus providing a good opportunity to investigate the role that kidney disease plays in the development of cardiovascular disease.

METHODS

We assessed 70 patients, aged 4 months to 18 years, with chronic kidney disease stages 3-5, for known risk factors of cardiovascular disease and for additional laboratory and clinical variables which may have an impact on this disease process. Carotid artery ultrasound was used to evaluate vascular structure and function, whereas myocardial disease was assessed by echocardiography.

RESULTS

Traditional risk factors, although present in this cohort, did not accumulate with progression of chronic kidney disease. Non-traditional risk factors increased in number and severity in correlation with the stage of CKD. The main myocardial abnormalities were left ventricular hypertrophy and diastolic dysfunction. Vascular function tests correlated with calcium-phosphate metabolism variables, homocysteine and time-averaged serum uric acid.

CONCLUSIONS

This study shows that children with CKD are exposed to risk factors and demonstrate signs of cardiovascular disease already at a young age. The possible role of uric acid and homocysteine in the evolution of cardiovascular disease is discussed. Further studies looking at possible interventions to prevent cardiovascular morbidity and mortality in this high risk population are needed.

Congenital analbuminemia with acute glomerulonephritis: a diagnostic challenge

Congenital analbuminemia is a rare autosomal recessive disease in which albumin is not synthesized. Patients with this disorder generally have minimal symptoms despite complete absence of the most abundant serum protein. We report a family in which the proband presented with acute glomerulonephritis and was found to have underlying congenital analbuminemia. Consequently, the patient's two older sisters were diagnosed with the same condition. Sequencing of the human serum albumin gene was performed, and a homozygous mutation in exon 3 was found in all three patients. Together with these three patients of Arab ethnicity, this mutation, known as Kayseri, is the most frequently described mutation in congenital analbuminemia. This article discusses clinical features and diagnostic challenges of this disorder, particularly in this case, where concomitant renal disease was present.

Misleading findings of homozygosity mapping resulting from three novel mutations in NPHS1 encoding nephrin in a highly inbred community

PURPOSE

Congenital nephrotic syndrome of the Finnish type (CNF, NPHS1) is a rare autosomal recessive disease caused by mutations in the NPHS1 gene encoding nephrin. We diagnosed congenital nephrotic syndrome in 12 children living in a village near Jerusalem. Most of the inhabitants are descendants of one Muslim family and have maintained their isolation by preference of consanguineous marriages. The aim of this study was to confirm that the NPHS1 gene is responsible for congenital nephrotic syndrome in our population, applying homozygosity mapping.

METHODS

DNA samples were genotyped by four microsatellite markers that were in linkage disequilibrium with the NPHS1 gene on chromosome 19q13.1. Immunoperoxidase staining was used to study the expression of nephrin, and mutations were subsequently identified by direct sequencing of the entire coding region of the NPHS1 gene.

RESULTS

Haplotype analysis revealed several different haplotypes, leading us to assume erroneously that there was genetic heterogeneity of congenital nephrotic syndrome. Because nephrin was completely absent in kidney tissue of one patient, direct sequencing of all DNA samples was performed, yielding three novel mutations: c.1138C>T (p.Gln380X), c.2160_ 2161insC (p.Cys721fs), and c.1707C>G (p.Ser569Arg). Patients were either homozygous for one of these mutations or compound heterozygotes, and they differed in their phenotype.

CONCLUSION

We report the potential pitfalls of performing homozygosity mapping in a highly consanguineous population and discuss the phenomenon of multiple mutations in a given gene within an isolate.

Hyperostosis-hyperphosphatemia syndrome: a congenital disorder of O-glycosylation associated with augmented processing of fibroblast growth factor 23

Two hyperphosphatemic patients with mutations in GALNT3 showed low intact FGF23 levels with marked increase of processed C-terminal fragments. FGF23 protein has three O-linked glycans and FGF23 with incomplete glycosylation is susceptible to processing. Silencing GALNT3 resulted in enhanced processing of FGF23. Decreased function of FGF23 by enhanced processing is the cause of hyperphosphatemia in patients with GALNT3 mutation.

INTRODUCTION

Hyperostosis-hyperphosphatemia syndrome (HHS) is an autosomal recessive entity manifesting as severe hyperphosphatemia associated with episodic bone pain and radiological findings of cortical hyperostosis and periosteal reaction. Persistent hyperphosphatemia is not counterbalanced by PTH or 1,25-dihydroxyvitamin D, posing a mirror image of hypophosphatemic states attributed to increased fibroblast growth factor (FGF)23 activity.

MATERIALS AND METHODS

We describe two children with HHS who were found to be homozygous for a mutation in GALNT3 encoding a peptide involved in mucin-type O-glycosylation (ppGaNTase-T3). FGF23 levels were evaluated by two ELISAs and Western blotting. FGF23 protein was analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Effect of silencing GALNT3 was evaluated using siRNA in cells transfected with expression vector for FGF23.

RESULTS

Both patients had low levels of the full-length FGF23 with markedly augmented amounts of the inactive fragments. Biologically active FGF23 has three O-linked glycans. FGF23 with only one or two O-linked glycans is processed into inactive fragments. Decreasing the expression of the GALNT3 gene by RNA interference resulted in enhanced processing of FGF23.

CONCLUSIONS

The primary defect in HHS is impairment of glycosylation of FGF23 resulting from mutations in GALNT3 and leading to augmented processing of FGF23. These changes in FGF23 abolish its phosphaturic effect and lead to severe persistent hyperphosphatemia. This study provides the pathogenetic mechanism of the first mucin-type O-glycosylation defect identified.

Recurrent nephrotic syndrome in homozygous truncating NPHS2 mutation is not due to anti-podocin antibodies

Mutations in NPHS2 are a common cause of focal segmental glomerulosclerosis (FSGS). It was initially assumed that FSGS caused by a genetically defective protein in the native kidney would not recur after transplantation; however, description of three patients with NPHS2 missense mutations challenged the validity of this assumption. A possible mechanism of recurrence in cases with stop-codon mutations is the formation of auto-antibodies against the truncated protein. In this case report, we describe a 9-year-old girl with the R138X NPHS2 mutation who presented with recurrent nephrotic syndrome 4 years after renal transplantation from a deceased donor, and was treated with plasmapheresis with a partial response. Renal histology did not demonstrate glomerular immunoglobulin deposition and an extensive search for anti-podocin antibodies based on indirect Western blot with recombinant podocin, was negative, as was the test for glomerular permeability factor (Palb). Taken together these findings confirm the possibility of post transplantation nephrotic syndrome in patients with NPHS2 mutations. Lack of immunoglobulin deposition, absence of circulating anti-podocin antibodies, and normal Palb suggest that other, unknown pathogenetic mechanisms are implicated.

Hyperphosphatemia is prevalent among children with nephrotic syndrome and normal renal function

The aim of the study was to analyze systematically our observation that children with severe nephrotic syndrome (NS) have hyperphosphatemia despite normal kidney function. Forty-seven children with NS and normal glomerular filtration rate (GFR) were studied [26 with steroid-sensitive nephrotic syndrome (SSNS) and 21 with persistent NS]. The plasma phosphate level was expressed as the number of standard deviations (SDs) from the mean levels in age- and gender-matched controls. In SSNS plasma phosphate concentration was elevated (+3.7+/-2.0 SDs) during relapse and normalized (-0.7+/-1.7 SDs) in remission. In persistent NS the phosphate level was +4.0+/-2.1 SDs. Patients with marked hyperphosphatemia (>4 SDs) were younger (p<0.001), had lower plasma albumin (p<0.001), and had higher urinary protein levels (p<0.05). Hyperphosphatemia did not correlate with GFR, plasma calcium, or urinary sodium levels. Children with persistent NS had decreased serum 25(OH)D(3) and insulin-like growth factor 1 (IGF-1) concentrations. Hyperphosphatemia is prevalent among children with persistent nephrotic syndrome and normal renal function, correlates with its severity, and may result from increased urinary IGF-1 wasting.

Risk factors for cardiovascular disease in children and young adults after renal transplantation

Despite good outcomes in pediatric renal transplantation, life expectancy is reduced, mostly as a result of accelerated atherosclerosis. A comprehensive evaluation of cardiac status and risk factors for cardiovascular disease was performed in 60 patients after renal transplantation (age 3 to 29 yr; mean 15.8). Posttransplantation diabetes was diagnosed in 7%. Half of the patients did not engage in any physical activity, and this was associated with increased body mass index. Uncontrolled hypertension was found in 13% of patient, and 53% were on antihypertensive medications. BP index was associated with left ventricular mass index (LVMI). Dyslipidemia was relatively uncommon, with hypercholesterolemia found in 15% and elevated LDL cholesterol found in 10% of patients. Hyperhomocysteinemia was frequent (58%); in most patients, it was not due to folate or B(12) deficiency. Lipid and homocysteine abnormalities were associated with cyclosporine therapy. Echocardiography demonstrated normal LVMI in 93% of patients, although LVMI was higher than in healthy control subjects. Cardiac troponin I was normal in all patients, but N-terminal pro-brain natriuretic peptide was elevated in 35% and was associated with LVMI and renal function. Although present cardiac status is relatively normal in pediatric renal transplantation patients, cardiac risk factors are common, and strategies to prevent cardiovascular disease need to be developed.

Molecular, biochemical, and genetic characterization of a female patient with Lesch-Nyhan disease

Lesch-Nyhan disease (LND) is a rare X-linked recessive disorder caused by virtually complete deficiency of activity of the purine salvage enzyme hypoxanthine phosphoribosyltransferase (HPRT; EC 2.4.2.8). Human HPRT is encoded by a single structural gene located on the long arm of the X-chromosome (Xq26). The classical LND phenotype occurs almost exclusively in males, manifested in excessive purine production and characteristic neurological manifestations, including compulsive self-mutilation, choreoathetosis, spasticity, and occasionally developmental delay. Heterozygous females are usually phenotypically normal, due to the random inactivation of the X chromosome (Lyonization mechanism). However, six females were reported to be affected with the full biochemical and clinical manifestations of LND. All these cases were heterozygous for an HPRT mutation. Absence of transcription of the normal HPRT allele was attributed in all of them to non-random inactivation of the X chromosome carrying the normal allele. Here we describe an additional LND female, who presented with acute renal failure at the age of two months, in whom absence of transcription of the two HPRT alleles occurred due to as yet undescribed mechanism in LND females: the transcription of one HPRT allele was blocked due to a de novo X chromosome-autosome translocation 46,XX,t(X:2)(q26:p25), with a breaking point encompassing the HPRT gene locus, whereas the transcription of the normal allele was inhibited due to non-random inactivation of the second X-chromosome. Cultured fibroblasts from this patient exhibited the biochemical alterations in purine nucleotide metabolism characteristic of male LND fibroblasts.

The Heart of Children with Steroid-Resistant Nephrotic Syndrome: Is It All Podocin?

Mutations in the gene NPHS2 encoding podocin are responsible for a recessive form of steroid-resistant nephrotic syndrome (SRNS). The common phenotype is of massive proteinuria in early childhood that tends to progress to end-stage renal failure. Extrarenal manifestations have not been described. Twenty-two children with SRNS from six unrelated Arab families were found to be homozygous for the R138X mutation in NPHS2. Eighteen patients underwent cardiac evaluation at diagnosis of SRNS while they had normal BP and preserved renal function. Cardiac anomalies were detected in 16 (89%) children: Left ventricular hypertrophy in eight, pulmonary stenosis in six, discrete subaortic stenosis in two, and Ebstein anomaly and ventricular septal defect in one each. The remaining four affected individuals were assessed only once they had end-stage renal failure. They had severe left ventricular hypertrophy and experienced repeated episodes of heart failure. Two control groups were equally evaluated. The first consisted of 37 siblings without nephrotic syndrome, of whom only one carrier had a cardiac defect (P < 0.001). None of the second group, which included 22 children with persistent nephrotic syndrome as a result of other causes, had a cardiac anomaly (P < 0.001). Cardiac disorders in homozygotes for mutations in NPHS2 cannot be attributed to an association by chance or to a state of persistent nephrotic syndrome. Because human podocin mRNA is expressed in fetal heart, it is speculated that it may have a role in normal cardiac development. Cardiac evaluation is recommended at the time of diagnosis of SRNS due to mutations in podocin.

A Comprehensive Assessment of Renal Function in Patients With Gaucher Disease

BACKGROUND

Gaucher disease (GD) is caused by deficiency of acid beta-glucocerebrosidase and is the most common lysosomal storage disease. Patients may have massive hepatosplenomegaly, severe bone disease, and, occasionally, pulmonary or neurological involvement. Although other storage diseases, such as Fabry disease, frequently affect the kidneys, reports of renal abnormalities in patients with GD are limited to case reports. Our aim was to perform a comprehensive evaluation of renal function in patients with GD.

METHODS

Evaluation was performed at routine clinic visits and included blood pressure recording and renal ultrasound. Serum chemistries, urinalysis, urine electrolytes, total protein, and tubular proteinuria were assessed, and estimated glomerular filtration rate (GFR) was calculated.

RESULTS

One hundred sixty-one patients underwent evaluation, including 26 children. GFR was significantly greater in patients with GD than in age- and sex-matched healthy controls (P = 0.01 in men, P < 0.001 in women, P = 0.003 in children). Subgroups of patients with markers of more severe disease had a greater GFR than other patients. No patient had decreased renal function. Significant proteinuria was found only in patients with such comorbidities as diabetes mellitus or multiple myeloma. No evidence of renal tubular abnormalities was found, and kidney sonographic appearance and size were normal.

CONCLUSION

Despite the multiorgan nature of the disease, a systematic evaluation did not find renal abnormalities in patients with GD. Glomerular hyperfiltration was observed in a proportion of patients, particularly those with markers of more severe disease. This phenomenon does not seem to be associated with a subsequent decline in renal function.

Intra-familial clinical heterogeneity: absence of genotype-phenotype correlation in primary hyperoxaluria type 1 in Israel

BACKGROUND/AIMS

Primary hyperoxaluria type 1 (PH1) is caused by the deficiency of the liver enzyme alanine:glyoxylate aminotransferase which results in increased synthesis and excretion of oxalate. The clinical manifestations of PH1 are heterogeneous with respect to the age of onset and rate of progression. The aim of this study was to investigate possible relationships between a given genotype, the biochemical profile and the clinical phenotype.

METHODS

We conducted a study of 56 patients from 22 families with PH1 from Israel. The clinical and biochemical data were compiled and the genotype was determined for each family.

RESULTS

The prevalent phenotype was of early onset with progression to end-stage renal disease during the first decade of life. Fifteen PH1-causing mutations were detected in 21 families: 10 were first described in this patient population. Marked intra-familial clinical heterogeneity was noted, meaning that there was no correlation between a given genotype and the phenotype.

CONCLUSIONS

The clinical course of patients with PH1 is not dictated primarily by its genotype. Other genetic and/or environmental factors play a role in determining the ultimate phenotype.

Is noncompliance among adolescent renal transplant recipients inevitable?

OBJECTIVE

To evaluate the prevalence of noncompliance and factors that influence poor adherence to immunosuppressive drug regimens among kidney transplant recipients.

METHODS

We reviewed immunosuppressive drug compliance in 79 posttransplant patients. Patient self-report and low plasma calcineurin inhibitor levels served as indicators of noncompliance.

RESULTS

The prevalence of noncompliance was found to be highest in adolescents who were responsible for their own medications and who underwent cadaveric kidney transplantation (CTx; 45.5%) and lower after living related transplantation (28.6%). There were no documented cases of noncompliance among any recipient of living unrelated (commercial) transplantation. Among 13 noncompliant patients, the first indication of "drug holiday" was low plasma calcineurin inhibitor levels in 11 children. Two additional children presented with acute rejection. In 7 patients, repeated episodes of "drug holidays" led to acute rejection later: 21.4 +/- 13.2 months after the first decrease in plasma calcineurin inhibitor level had been recorded. All 9 patients who experienced acute rejection subsequently developed chronic rejection. In 4 patients, noncompliance did not influence graft function. Psychosocial factors that were associated with noncompliance included insufficient family support, low self-awareness caused by poor cognitive abilities, and denial.

CONCLUSIONS

The absence of cases of noncompliance in adolescents who underwent commercial living unrelated kidney transplantation suggests that although noncompliance is prevalent, it is not inevitable. Strategies to decrease noncompliance in young patients with chronic illnesses can be learned from the experience with transplant recipients. The general pediatrician has a central role in identifying and addressing the problem of noncompliance in adolescents with chronic disease.

Mutated podocin manifesting as CMV-associated congenital nephrotic syndrome

We report a girl with congenital nephrotic syndrome (CNS) associated with cytomegalovirus (CMV) infection and histological findings on renal biopsy that suggested a causal relationship between the two. She was subsequently found to be homozygous for a nonsense mutation in the NPHS2 gene encoding podocin (R138X), which is the true cause of her NS. Based on review of the literature and our findings in this patient, we propose that the clinical entity known as CMV causing CNS may not exist.

Hyperhomocysteinemia in children on renal replacement therapy

Hyperhomocysteinemia is an independent risk factor for the development of atherosclerosis in adult patients on dialysis or after kidney transplantation. There are few data on homocysteine (Hcy) concentrations in children under these circumstances. The aim of our study was to evaluate plasma Hcy levels and their determining factors in children on renal replacement therapy. In 29 children and adolescents on chronic dialysis therapy and in 34 children after renal transplantation (Tx) fasting total plasma Hcy, red blood cell (RBC) folate, and serum vitamin B(12) levels were measured. The plasma Hcy levels were expressed as number of standard deviations (SD) from mean level in age- and gender-matched controls. In dialysis patients the mean plasma Hcy level was elevated (4.4+/-0.8 SDs), without significant difference between patients on hemodialysis or continuous cycling peritoneal dialysis. In the dialysis patients a negative correlation ( r=-0.49) between plasma Hcy levels and RBC folate concentrations was found. Oral folate supplementation was given to 8 of 21 dialysis patients, resulting in high RBC folate levels (>800 micro g/ml) and normalization of the plasma Hcy levels (0.4+/-0.5 SDs). In Tx patients the mean plasma Hcy level was 5.6+/-1.4 SDs. Multivariate regression analysis revealed that the main factor determining Hcy level after kidney Tx was creatinine clearance. Patients with normal kidney function had a mean Hcy concentration of 1.69+/-0.86 compared with 10.0+/-2.2 in children with decreased function. Folate and cyclosporine levels had less significant effects on Hcy concentrations. Seven patients who were evaluated while on dialysis and after a successful kidney Tx demonstrated a significant reduction in Hcy levels. Children and adolescents on dialysis therapy and with impaired renal function after renal Tx have significant hyperhomocysteinemia. Oral folate supplementation normalizes the increased plasma Hcy levels and should be added to the medical treatment of all children with impaired renal function.

Severe reversible renal failure due to naproxen-associated acute interstitial nephritis

Acute interstitial nephritis is uncommon in children and has very rarely been described with naproxen treatment. We report the occurrence of severe acute renal failure in a 10-year-old girl with juvenile rheumatoid arthritis after 1 month of naproxen therapy. Renal biopsy showed severe acute interstitial nephritis. The patient recovered completely after discontinuation of naproxen and administration of methylprednisolone. A review of the literature regarding non-steroidal anti-inflammatory drug-associated acute interstitial nephritis is provided.

CONCLUSION

In an era of increasing popularity of non-steroidal anti-inflammatory drugs for use in children, paediatricians should be aware of the potential renal complications of this class of drugs.

Erythropoietin deficiency causes anemia in nephrotic children with normal kidney function

Anemia in persistent nephrotic syndrome (NS) has been described in a few case reports but has not been studied systematically. We present a group of 19 children with NS who developed anemia before the deterioration of kidney function. The aim of our study is to determine whether erythropoietin (EPO) and/or iron deficiency are causative factors and to evaluate the effect of EPO replacement therapy. Serum EPO levels, iron status, and vitamin B(12) concentrations were measured in nephrotic patients with anemia (NS-A) and compared with those of nephrotic children with normal hemoglobin (Hb) levels (NS-NHb; n = 13). Two control groups consisted of age-matched patients without kidney disease or hypoxemia with either iron deficiency anemia (IDA; n = 19) or normal Hb concentrations (NHb; n = 16). Most NS-A patients experienced persistent steroid-resistant NS, whereas most NS-NHb children had steroid-responsive NS. Although serum iron, ferritin, and B(12) levels were significantly lower in NS-A children, appropriate replacement therapy that resulted in normalization of ferritin and/or cobalamin levels did not lead to correction of the anemia. NS-A patients had greater EPO levels than those without anemia (21.6 +/- 3.3 versus 5.5 +/- 0.8 IU/L; P: < 0.001), but their response to anemia was inappropriately low compared with IDA children (EPO, 94.6 +/- 15.1 IU/L) despite similar Hb concentrations. EPO therapy for 4 to 9 months in 6 NS-A children with Hb levels less than 9 g/dL led to resolution of the anemia. In conclusion, anemia is a common feature of persistent NS that develops before the deterioration of kidney function. Depletion of iron stores may contribute to the development of anemia, but iron replacement therapy is ineffective. Nephrotic patients have EPO deficiency with a blunted response to anemia. The EPO deficiency is amenable to EPO therapy, which is recommended for this group of patients.

Genetic polymorphism in paraoxonase is a risk factor for childhood focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is an important cause of end-stage renal failure (ESRF) in children. Our previous studies have shown that Arab children in Israel have a worse prognosis compared with Jewish patients despite similar clinical presentation and management. Progression of proteinuric glomerular diseases has been associated with alterations in lipid metabolism, and similarities have been drawn between the mechanisms underlying atherosclerosis and glomerulosclerosis. Paraoxonase (PON) is a high-density lipoprotein (HDL)-associated enzyme involved in preventing the oxidation of low-density lipoprotein (LDL), and an association has been shown between two genetic polymorphisms in PON1 and the risk of coronary artery disease. The aim of this study was to determine the frequency of these genetic polymorphisms in PON1 in Arab and Jewish children with FSGS and to determine any association with severity of outcome. Forty-seven children (21 Arab and 26 Jewish) with biopsy-proven FSGS and 274 healthy controls of matching ethnic origin were studied. The glutamine (A)-192-arginine (B) and the methionine (M)-55-leucine (L) polymorphisms were analyzed. The frequency of the A allele was similar in patients and controls (0.68 versus 0.71), as was that of the L allele (0.63 versus 0.6). When subgroups were analyzed, the prevalence of the LL genotype in Arab patients was significantly greater than in Jewish patients (57.1% versus 26.9%, P: < 0.05) and Arab controls (57.1% versus 28.9%, P: < 0.03). A trend in association was found between homozygosity for the L allele and progression of renal disease in Arab children. Homozygosity for the L allele is a risk factor for developing FSGS in Arab children and may be associated with a worse prognosis.

Genetic polymorphisms of the renin-angiotensin system and the outcome of focal segmental glomerulosclerosis in children

BACKGROUND

The clinical course of primary focal segmental glomerulosclerosis (FSGS) in children is variable, with some patients having a much more rapidly progressing course than others. The purpose of our study was to compare the frequency of three polymorphisms of the renin-angiotensin system (RAS) in children with FSGS with that in healthy controls of matching ethnic groups, and to determine whether the clinical outcome of FSGS was associated with different RAS genotypes.

METHODS

Three RAS genotypes were examined in 47 Jewish and Arab children with biopsy-proven primary FSGS and in a large control group: the ACE insertion/deletion polymorphism in intron 16, the M235T mutation in the angiotensinogen gene, and the A1166C in the angiotensin II type 1 receptor gene (AT1R).

RESULTS

Arab patients showed a greater tendency towards progressive renal disease than their Jewish counterparts (12 of 21 vs. 9 of 26, P = 0.05) and were less likely to achieve remission (3 of 21 vs. 11 of 26, P < 0.04), despite similar clinical presentation, medical management and follow-up. The RAS allele prevalence was similar among patients and controls of matching ethnic backgrounds, and no difference in allele frequency was found between Arabs and Jews. Homozygotes for the ACE insertion genotype (II) were significantly less likely to have progressive renal disease than patients with the other genotypes (ID and DD; 0 of 6 vs. 21 of 41; P < 0.022). The other RAS polymorphisms were not associated with variations in the clinical course of childhood FSGS.

CONCLUSIONS

Homozygosity for the ACE insertion allele may have a protective effect in children with FSGS and can serve as a positive prognostic indicator at diagnosis. The D allele may exert a detrimental dominant effect on outcome. Neither the ACE gene polymorphism nor the other RAS polymorphisms studied are associated with disease prevalence. The AT1R and angiotensinogen gene polymorphisms are not associated with progression of renal disease in FSGS. Ethnic differences in the clinical course of the disease are not linked to these polymorphisms.