Peter Trnka

Defects in the IFT-B Component IFT172 Cause Jeune and Mainzer-Saldino Syndromes in Humans

Intraflagellar transport (IFT) depends on two evolutionarily conserved modules, subcomplexes A (IFT-A) and B (IFT-B), to drive ciliary assembly and maintenance. All six IFT-A components and their motor protein, DYNC2H1, have been linked to human skeletal ciliopathies, including asphyxiating thoracic dystrophy (ATD; also known as Jeune syndrome), Sensenbrenner syndrome, and Mainzer-Saldino syndrome (MZSDS). Conversely, the 14 subunits in the IFT-B module, with the exception of IFT80, have unknown roles in human disease. To identify additional IFT-B components defective in ciliopathies, we independently performed different mutation analyses: candidate-based sequencing of all IFT-B-encoding genes in 1,467 individuals with a nephronophthisis-related ciliopathy or whole-exome resequencing in 63 individuals with ATD. We thereby detected biallelic mutations in the IFT-B-encoding gene IFT172 in 12 families. All affected individuals displayed abnormalities of the thorax and/or long bones, as well as renal, hepatic, or retinal involvement, consistent with the diagnosis of ATD or MZSDS. Additionally, cerebellar aplasia or hypoplasia characteristic of Joubert syndrome was present in 2 out of 12 families. Fibroblasts from affected individuals showed disturbed ciliary composition, suggesting alteration of ciliary transport and signaling. Knockdown of ift172 in zebrafish recapitulated the human phenotype and demonstrated a genetic interaction between ift172 and ift80. In summary, we have identified defects in IFT172 as a cause of complex ATD and MZSDS. Our findings link the group of skeletal ciliopathies to an additional IFT-B component, IFT172, similar to what has been shown for IFT-A.

Henoch-Schönlein purpura in children.

Henoch–Schönlein purpura is the most common systemic vasculitis of childhood. In the majority of children, the outcome of Henoch–Schönlein purpura is excellent with spontaneous resolution of symptoms and signs. However, a small subset of patients will develop long‐term sequelae in the form of chronic kidney disease. While the clinical presentation and diagnosis of Henoch–Schönlein purpura is straightforward, treatment of Henoch–Schönlein purpura nephritis and long‐term renal outcomes of more severely affected children are less certain. This review article gives a general overview of Henoch–Schönlein purpura with emphasis on recently published information, including the new classification of childhood vasculitis, insights into pathogenesis of Henoch–Schönlein purpura and a summary of various treatments of established Henoch–Schönlein purpura nephritis.

Congenital urinary tract obstruction: defining markers of developmental kidney injury

Congenital urinary tract obstruction (diagnosed antenatally by ultrasound screening) is one of the main causes of end-stage kidney disease in children. The extent of kidney injury in early gestation and the resultant abnormality in kidney development determine fetal outcome and postnatal renal function. Unfortunately, the current approach to diagnostic evaluation of the severity of injury has inherently poor diagnostic and prognostic value because it is based on the assessment of fetal tubular function from fetal urine samples rather than on estimates of the dysplastic changes in the injured developing kidney. To improve the outcome in children with congenital urinary tract obstruction, new biomarkers reflecting these structural changes are needed. Genomic and proteomic techniques that have emerged in the past decade can help identify the key genes and proteins from biological fluids, including amniotic fluid, that might reflect the extent of injury to the developing kidney.

Urinary Biomarkers in Obstructive Nephropathy

BACKGROUND AND OBJECTIVES Obstructive nephropathy is a leading cause of CKD in children. The assessment of severity of renal impairment and the prediction of which children will progress to renal failure are, however, challenging. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS This case-control study measured the urinary excretion of candidate biomarkers in 27 prevalent case-patients with posterior urethral valves (PUVs) and 20 age-matched controls, correlated their urinary concentration with GFR, and analyzed receiver-operating characteristic (ROC) curve and regression analyses to assess their performance as tests for low GFR. RESULTS The median urinary protein-to-creatinine ratio was higher in children with PUV (45 g/mol; range, 5-361 g/mol) than in controls (7 g/mol; range, 3-43 g/mol) (P<0.01) and correlated inversely with renal function (r = -0.44; P<0.05). In whole urine, excretion of aquaporin-2 was significantly decreased, whereas that of TGFβ and L1 cell adhesion molecule (L1CAM) was significantly increased. Whole-urine TGFβ excretion correlated inversely with GFR (r = -0.53; P<0.05). As tests for low GFR, whole-urine TGFβ, L1CAM, and urinary protein-to-creatinine ratio performed best, with areas under the ROC curves of 0.788, 0.795, and 0.814, respectively. By linear regression analysis, whole-urine TGFβ, L1CAM, and urinary protein-to-creatinine ratio were associated with low GFR in the case-patients. CONCLUSIONS Candidate biomarkers of obstructive nephropathy can be readily measured in whole urine and in urine exosomes. In boys with PUV, these biomarkers correlate with GFR.

Urinary tract obstruction in the mouse: the kinetics of distal nephron injury

Congenital urinary tract obstruction is the single most important cause of childhood chronic kidney disease. We have previously demonstrated that human and primate fetal obstruction impairs the development, differentiation, and maturation of the kidney. Research using postnatal rodent models has primarily focused upon the role of proximal tubular injury, with few reports of collecting duct system pathology or the suitability of the postnatal models for examining injury to the distal nephron. We have employed the mouse unilateral ureteric obstruction (UUO) model and examined time points ranging from 1 to 14 days of obstruction. Many of the key features of fetal collecting duct injury are replicated in the postnatal mouse model of obstruction. Obstruction causes a sixfold increase in myofibroblast accumulation, two- to threefold dilatation of tubules of the distal nephron, 65% reduction of principal cell aquaporin 2 expression, 75% reduction of collecting duct intercalated cell abundance, and disruption of E-cadherin- and βcatenin-mediated collecting duct epithelial adhesion. Notably, these features are shared by the distal and connecting tubules. This work confirms that distal nephron pathology is a significant component of postnatal mouse UUO. We have highlighted the utility of this model for investigating collecting duct and distal tubule injury and for identifying the underlying mechanisms of the distal nephron’s contribution to the repair and fibrosis.

Phenotypic transition of the collecting duct epithelium in congenital urinary tract obstruction.

Epithelial-mesenchymal transition (EMT) has emerged in recent years as an important process in the development of organ fibrosis in many human diseases. Our previous experience in a nonhuman primate model of obstructive nephropathy suggested that EMT of collecting duct epithelium contributes to the development of interstitial fibrosis. In this study we demonstrate for the first time in humans that obstructed fetal collecting duct epithelium undergoes transition to mesenchymal phenotype, characterized by decreased expression of epithelial markers, de novo expression of mesenchymal markers with subsequent loss of cell-cell interaction, disruption of the basement membrane, and increased deposition of extracellular matrix into the expanded interstitium of the obstructed kidney. The results of this study therefore support the previous findings from animal studies and suggest that EMT of the collecting duct epithelium might contribute to the development of interstitial fibrosis in human fetal obstructive nephropathy.

Long-Term Outcome of Kidney Transplantation in Recipients with Focal Segmental Glomerulosclerosis

BACKGROUND AND OBJECTIVES FSGS can recur after kidney transplantation and is associated with poor graft outcomes. We aimed to assess the incidence of FSGS recurrence post-transplant and determine the effect of graft source on recurrence and graft survival in patients with biopsy-proven FSGS. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS Using the Australian and New Zealand Dialysis and Transplant Registry, we assessed incidence of FSGS, the influence of donor type on the risk of FSGS recurrence, and graft loss in recipients with ESRD caused by primary FSGS using Kaplan-Meier and logistic regression analyses. RESULTS Between 1992 and 2011, 736 first kidney transplants were performed in 666 adults and 70 children (≤20 years old) with biopsy-proven primary FSGS. FSGS recurred in 76 (10.3%) patients. Younger age (P<0.001), nonwhite ethnicity (P=0.02), and having a live donor (P=0.02) were independent risk factors associated with recurrence. Median graft survival was significantly better for live donor compared with deceased donor grafts (14.8 versus 12.1 years; P<0.01). Disease recurrence predicted poor graft outcomes, with 52% (95% confidence interval, 40% to 63%) 5-year graft survival in the recurrence group compared with 83% (95% confidence interval, 79% to 86%) in the group without recurrent disease (P<0.001). CONCLUSIONS FSGS recurrence after kidney transplantation was more common in live donor kidneys. Despite this, graft survival in live donor recipients was significantly better for both children and adults with FSGS. We propose that live donor transplantation should not be avoided in patients with FSGS.

KHA‐CARI guideline: Diagnosis and treatment of urinary tract infection in children

Child & Adolescent Renal Service, Royal Children’s and Mater Children’s Hospitals, University of Queensland, Department of Paediatrics and Child Health, The University of Queensland, Brisbane, Queensland, Department of General Medicine, The Royal Children’s Hospital, Vaccine and Immunisation Research Group and Rotavirus Research Group, Murdoch Childrens Research Institute, Department of Paediatrics, The University of Melbourne, Paediatric Imaging, Monash Health, Monash University, Department of Nephrology, Royal Children’s Hospital Melbourne, Murdoch Childrens Research Institute, University of Melbourne, Melbourne, Victoria, Department of Nephrology, Princess Margaret Hospital for Children, Perth, Western Australia, Nephrology, Sydney Children’s Hospital, School of Women’s & Children’s Health, University of New South Wales, and Centre for Kidney Research, The Children’s Hospital at Westmead, Sydney, New South Wales, Australia

Reninoma: an uncommon cause of renin-mediated hypertension

Reninoma (juxtaglomerular cell tumor) is a rare cause of renin-mediated hypertension. Reninomas are usually diagnosed in adolescents and young adults with occasional reports in younger children. Patients typically present with a long history of headaches leading to a diagnosis of severe hypertension that responds well to antihypertensive treatment targeting the renin-angiotensin-aldosterone system. The clue to clinical diagnosis is the presence of hypokalemia and metabolic alkalosis on the first blood sample drawn before any treatment is instituted. Elevated blood levels of renin and aldosterone confirm the clinical suspicion of renin-mediated hypertension. Diagnostic imaging is employed to identify the source of excessive renin production. While renal ultrasound can miss reninoma, contrast CT or magnetic resonance imaging of the kidneys are diagnostic modalities of choice leading to the correct diagnosis. Renal vein renin sampling with lateralization might help to identify the site of excessive renin production. Nephron-sparing surgery is curative with maintenance of normal blood pressure after discontinuation of antihypertensive medications in the majority of patients. In this paper, we present the case of reninoma in an adolescent girl emphasizing clinical presentation, diagnostic evaluation, and medical and surgical treatment of this rare tumor. We also discuss important points in the management of children presenting with renin-mediated hypertension.

Selected Primary Care Issues and Comorbidities in Children Who Are on Maintenance Dialysis: A Review for the Pediatric Nephrologist

Ten-year survival of all children who initiate dialysis at any age now approaches 70%, and in the older child this number is closer to 80%. These children will live with chronic kidney disease and its myriad of associated comorbidities during and throughout their childhood. Their care is complex and requires both teamwork and careful attention paid to maintaining lines of communication among patient, family, and both the facility-based nephrology team and caregivers who are outside the hospital setting. Irrespective of their need for dialysis, children with ESRD deserve and require developmentally appropriate care and anticipatory guidance with respect to primary care issues of childhood. The child who is on dialysis often is cared for solely or in large part by a nephrology service, therefore this review discusses issues that are particularly important to pediatric nephrologists in relation to selected primary care issues and comorbidities for the child who is on dialysis, with an emphasis on medical and psychosocial issues, and with particular weight placed on issues that are pertinent to the adolescent dialysis patient.