Sevgi Mir

Novel ATP6V1B1 and ATP6V0A4 mutations in autosomal recessive distal renal tubular acidosis with new evidence for hearing loss

Autosomal recessive distal renal tubular acidosis (rdRTA) is characterised by severe hyperchloraemic metabolic acidosis in childhood, hypokalaemia, decreased urinary calcium solubility, and impaired bone physiology and growth. Two types of rdRTA have been differentiated by the presence or absence of sensorineural hearing loss, but appear otherwise clinically similar. Recently, we identified mutations in genes encoding two different subunits of the renal α-intercalated cell’s apical H+-ATPase that cause rdRTA. Defects in the B1 subunit gene ATP6V1B1, and the a4 subunit gene ATP6V0A4, cause rdRTA with deafness and with preserved hearing, respectively. We have investigated 26 new rdRTA kindreds, of which 23 are consanguineous. Linkage analysis of seven novel SNPs and five polymorphic markers in, and tightly linked to, ATP6V1B1 and ATP6V0A4 suggested that four families do not link to either locus, providing strong evidence for additional genetic heterogeneity. In ATP6V1B1, one novel and five previously reported mutations were found in 10 kindreds. In 12 ATP6V0A4 kindreds, seven of 10 mutations were novel. A further nine novel ATP6V0A4 mutations were found in “sporadic” cases. The previously reported association between ATP6V1B1 defects and severe hearing loss in childhood was maintained. However, several patients with ATP6V0A4 mutations have developed hearing loss, usually in young adulthood. We show here that ATP6V0A4 is expressed within the human inner ear. These findings provide further evidence for genetic heterogeneity in rdRTA, extend the spectrum of disease causing mutations in ATP6V1B1 and ATP6V0A4, and show ATP6V0A4 expression within the cochlea for the first time.

COQ6 mutations in human patients produce nephrotic syndrome with sensorineural deafness

Steroid-resistant nephrotic syndrome (SRNS) is a frequent cause of end-stage renal failure. Identification of single-gene causes of SRNS has generated some insights into its pathogenesis; however, additional genes and disease mechanisms remain obscure, and SRNS continues to be treatment refractory. Here we have identified 6 different mutations in coenzyme Q10 biosynthesis monooxygenase 6 (COQ6) in 13 individuals from 7 families by homozygosity mapping. Each mutation was linked to early-onset SRNS with sensorineural deafness. The deleterious effects of these human COQ6 mutations were validated by their lack of complementation in coq6-deficient yeast. Furthermore, knockdown of Coq6 in podocyte cell lines and coq6 in zebrafish embryos caused apoptosis that was partially reversed by coenzyme Q10 treatment. In rats, COQ6 was located within cell processes and the Golgi apparatus of renal glomerular podocytes and in stria vascularis cells of the inner ear, consistent with an oto-renal disease phenotype. These data suggest that coenzyme Q10-related forms of SRNS and hearing loss can be molecularly identified and potentially treated.

Henoch-Schönlein nephritis: long-term prognosis of unselected patients.

Progressive glomerulonephritis is the most serious feature of Henoch-Schönlein syndrome. In a series of 141 children with Henoch-Schönlein purpura 39 (28%) had abnormal urinary sediment for a duration of more than one month. This subgroup was followed up for 3.0 to 13.8 (mean 7.2) years. One child progressed to renal failure and 2 developed chronic glomerular disease. In this series most of the patients with Henoch-Schönlein syndrome and nephritis had a good prognosis.

The Cardiovascular Comorbidity in Children with Chronic Kidney Disease (4C) Study: Objectives, Design, and Methodology

BACKGROUND AND OBJECTIVES Children and adolescents with chronic kidney disease (CKD) are at high risk for cardiovascular morbidity and mortality. A systemic arteriopathy and cardiomyopathy has been characterized in pediatric dialysis patients by the presence of morphologic and functional abnormalities. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS The Cardiovascular Comorbidity in Children with CKD (4C) Study is a multicenter, prospective, observational study aiming to recruit more than 600 children, aged 6 to 17 years, with initial GFR of 10 to 45 ml/min per 1.73 m(2). The prevalence, degree, and progression of cardiovascular comorbidity as well as its association with CKD progression will be explored through longitudinal follow-up. The morphology and function of the heart and large arteries will be monitored by sensitive noninvasive methods and compared with aged-matched healthy controls. Multiple clinical, anthropometric, biochemical, and pharmacologic risk factors will be monitored prospectively and related to the cardiovascular status. A whole-genome association study will be performed to identify common genetic variants associated with progression of cardiovascular alterations and/or renal failure. Monitoring will be continued as patients reach end-stage renal disease and undergo different renal replacement therapies. RESULTS While cardiovascular morbidity in adults is related to older age and additional risk factor load (e.g., diabetes), the role of CKD-specific factors in the initiation and progression of cardiac and vascular disease are likely to be characterized with greater sensitivity in the pediatric age group. CONCLUSIONS The 4C study is expected to provide innovative insight into cardiovascular and renal disease progression in CKD.

Association of TLR2 gene Arg753Gln polymorphism with urinary tract infection in children.

The aim of this study is to investigate Arg753Gln allele polymorphisms of toll‐like receptor‐2 (TLR2) gene distribution, allele frequency in urinary tract infection (UTI) and genotype–phenotype association of TLR2 gene in children with UTI. The polymorphism was investigated in 124 children with UTI (22 boys and 102 girls; mean age 5.81 ± 3.47 years) with direct DNA sequencing‐based method. TLR2 gene Arg753Gln allele frequency was higher in the patient group when compared with control group (OR 3.14, 95%CI 1.53–6.44, P < 0.001). The frequency of the Arg753Gln allele was significantly higher in gram‐positive group than in gram‐negative group (OR 7.64, 95%CI 2.80–20.81, P < 0.001). The frequency of UTI was found significantly higher in the Arg753Gln allele carriers of TLR2 gene than the non‐carriers (OR 4.94, 95%CI 1.09–22.33, P < 0.05). Similarly, the incidence of asymptomatic UTI was also found significantly higher in the group carrying Arg753Gln allele (OR 3.73, 95%Cl 1.54–9.04, P < 0.05). As a result, we suggest that TLR2 gene could be the predisposing factor for urinary tract infection. Additionally, we observed that subjects carrying the TLR2 Arg753Gln allele had higher risk of urinary tract infection with gram‐positive pathogens, history of more than two attacks of UTI and asymptomatic UTI.

Clinical outcome in children with Henoch-Schönlein nephritis

Henoch-Schönlein purpura (HSP) is the most common vasculitis in childhood. The long-term prognosis is variable and depends on renal involvement. The aim of this study was to evaluate both clinical features of the children with HSP and the prognoses of short- and long-term outcome of patients diagnosed as HSP nephritis (HSN). This is a retrospective data study of all children with HSP hospitalized from January 1991 to December 2005. The patients with HSN were classified according to their initial presentation, histologic findings, type of treatment and clinical outcome. All patients have been evaluated once every 2 months. Fifty-three of the patients had kidney biopsies. The patient population consisted of 141 children included 78 boys (55.3%) and 63 girls (44.7%) ranging in age at disease onset from 2 to 17 (8.9±3.29) years. Renal involvement was determined in 58.1%. Nephrotic and/or nephritic syndrome were found to be an unfavorable predictor both for short and long-term outcome (P<0.05). However, 35% of these patients and 62% of them showed complete remission after 6 months and long-term course. Overall prognosis of HSN is relatively good and long-term morbidity is predominantly associated with initial presentation and renal involvement.

Genetic screening in adolescents with steroid-resistant nephrotic syndrome

Genetic screening paradigms for congenital and infantile nephrotic syndrome are well established; however, screening in adolescents has received only minor attention. To help rectify this, we analyzed an unselected adolescent cohort of the international PodoNet registry to develop a rational screening approach based on 227 patients with nonsyndromic steroid-resistant nephrotic syndrome aged 10-20 years. Of these, 21% had a positive family history. Autosomal dominant cases were screened for WT1, TRPC6, ACTN4, and INF2 mutations. All other patients had the NPHS2 gene screened, and WT1 was tested in sporadic cases. In addition, 40 sporadic cases had the entire coding region of INF2 tested. Of the autosomal recessive and the sporadic cases, 13 and 6%, respectively, were found to have podocin-associated nephrotic syndrome, and 56% of them were compound heterozygous for the nonneutral p.R229Q polymorphism. Four percent of the sporadic and 10% of the autosomal dominant cases had a mutation in WT1. Pathogenic INF2 mutations were found in 20% of the dominant but none of the sporadic cases. In a large cohort of adolescents including both familial and sporadic disease, NPHS2 mutations explained about 7% and WT1 4% of cases, whereas INF2 proved relevant only in autosomal dominant familial disease. Thus, screening of the entire coding sequence of NPHS2 and exons 8-9 of WT1 appears to be the most rational and cost-effective screening approach in sporadic juvenile steroid-resistant nephrotic syndrome.

Alterations of blood pressure in type 1 diabetic children and adolescents

The aim of this study was to assess the association between metabolic control, microalbuminuria, and diabetic nephropathy with ambulatory blood pressure monitoring (ABPM) in normotensive individuals with type 1 diabetes mellitus (DM). ABPM was undertaken in 68 normotensive type 1 diabetic patients with a mean age of 14.4±4.2 years. Microalbuminuria was diagnosed on the basis of a urinary albumin excretion rate grater than 20 μg/min in two of the three 24-h urine collections. Hypertension (HT) frequency was greater in the microalbuminuric patients than normoalbuminuric patients (54 vs 17.54%, p=0.05) with ABPM. Microalbuminuric patients had a higher diastolic pressure burden than normoalbuminuric patients. There were no differences in systolic and diastolic dips between the two groups. Diastolic pressure loads in all periods showed a significant correlation with duration of diabetes, mean HbA1c from the onset of diabetes, and level of microalbuminuria. Nocturnal dipping was reduced in 41.2% of the patients. In the normoalbuminuric group 41.1% and in the microalbuminuric group 63.6% were nondippers. Our data demonstrate higher 24-h and daytime diastolic blood pressure load and loss of nocturnal dip in type 1 diabetic adolescents and children. High diastolic blood pressure burden in diabetic patients could represent a risk for nephropathy.

Henoch-Schönlein nephritis: a nationwide study.

Background/Aim: The aim of this retrospective study was to evaluate the presentation, clinical and pathological manifestations and outcome of the Henoch-Schönlein purpura (HSP) nephritis in children. Methods: Clinical and laboratory data of 443 children with HSP nephritis aged between 3 and 16 years from 16 pediatric nephrology reference centers were analyzed retrospectively. The biopsy findings were graded according to the classification developed by the International Study of Kidney Disease in Children (ISKDC). Results: Renal biopsy was performed in 179 of the patients with HSP nephritis. The most common presenting clinical finding in patients who were biopsied was nephrotic range proteinuria (25%) which was followed by nephritic-nephrotic syndrome (23.5%). The biopsy findings according to the ISKDC were as follows: class I: 8.3%; II: 44.1%; III: 36.3%; IV: 6.7%; V: 3.3%; VI: 1.1%. All of the patients who developed end-stage renal disease had nephritic-nephrotic syndrome at presentation. Of 443 patients, 87.2% had a favorable outcome and 12.8% had an unfavorable outcome. The overall percentage of children who developed end-stage renal disease at follow-up was 1.1%. Logistic regression analysis did not show any association of initial symptoms and histology with outcome. Conclusion: In the presented cohort, the presence of crescents in the first biopsy or presenting clinical findings did not seem to predict the outcome of HSP nephritis in children. We conclude that children with HSP nephritis even with isolated microscopic hematuria and/or mild proteinuria should be followed closely.

TRPC6 gene variants in Turkish children with steroid-resistant nephrotic syndrome

BACKGROUND In steroid-resistant nephrotic syndrome (SRNS), a considerable number of patient progress to end-stage renal disease (ESRD), despite aggressive therapy. The latest advance in familial focal segmental glomerulosclerosis (FSGS) has been the discovery of a mutant form of canonical transient receptor potential channel 6 (TRPC6) leading to FSGS through unclear mechanisms. The aim of this study is to screen for TRPC6 mutations in familial and sporadic SRNS patients. METHODS Twenty-five children with SRNS originating from Turkey were included in this study. Nine patients had familial and 16 patients had sporadic SRNS. Mutation analysis was performed in all 13 coding exons of the TRPC6 gene with the direct DNA sequencing method. The control group consisted of 50 normal healthy children originating from Turkey. RESULTS No mutation was detected in nine children (four familial, five sporadic). A variant (L395A) in one patient, intronic nucleotide substitution (c.171 + 16 A>G and c.171 + 86 G>C) in six patients and previously described missense (A404V; rs36111323) and synonymous (N561N; rs12366144) aminoacid variants in nine patients were found. Among patients with intronic, missense and synonymous aminoacid variants, 5 patients had familial and 11 patients had sporadic SRNS. Their mean age at onset of proteinuria was 2.6 ± 1.7 years. Seven cases (three familial, four sporadic) progressed to ESRD with a mean time of 10.2 ± 2.9 years. CONCLUSIONS In conclusion, analysis of TRPC6 gene mutations in FSGS will provide new insights into the pathogenesis of nephrotic syndrome. Previous works have emphasized that the patients with only hereditary familial FSGS carried a missense mutation in the TRPC6 gene. Our findings suggest that TRPC6 mutations may also have an important role in the pathogenesis of sporadic SRNS.