Diverse ancestry whole-genome sequencing association study identifies TBX5 and PTK7 as susceptibility genes for posterior urethral valves.

Posterior urethral valves (PUV) are the commonest cause of end-stage renal disease in children, but the genetic architecture of this rare disorder remains unknown. We performed a sequencing-based genome-wide association study (seqGWAS) in 132 unrelated male PUV cases and 23,727 controls of diverse ancestry, identifying statistically significant associations with common variants at 12q24.21 (p=7.8 × 10-12; OR 0.4) and rare variants at 6p21.1 (p=2.0 × 10-8; OR 7.2), that were replicated in an independent European cohort of 395 cases and 4151 controls. Fine mapping and functional genomic data mapped these loci to the transcription factor TBX5 and planar cell polarity gene PTK7, respectively, the encoded proteins of which were detected in the developing urinary tract of human embryos. We also observed enrichment of rare structural variation intersecting with candidate cis-regulatory elements, particularly inversions predicted to affect chromatin looping (p=3.1 × 10-5). These findings represent the first robust genetic associations of PUV, providing novel insights into the underlying biology of this poorly understood disorder and demonstrate how a diverse ancestry seqGWAS can be used for disease locus discovery in a rare disease.

Identification of a novel genetic locus associated with immune-mediated thrombotic thrombocytopenic purpura.

Immune thrombotic thrombocytopenic purpura (iTTP) is an ultra-rare, life-threatening disorder, mediated through severe ADAMTS13 deficiency causing multi-system micro-thrombi formation, and has specific human leukocyte antigen associations. We undertook a large genome-wide association study to investigate additional genetically distinct associations in iTTP. We compared two iTTP patient cohorts with controls, following standardized genome-wide quality control procedures for single-nucleotide polymorphisms and imputed HLA types. Associations were functionally investigated using expression quantitative trait loci (eQTL), and motif binding prediction software. Independent associations consistent with previous findings in iTTP were detected at the HLA locus and in addition a novel association was detected on chromosome 3 (rs9884090, P=5.22x10-10, odds ratio 0.40) in the UK discovery cohort. Meta-analysis, including the French replication cohort, strengthened the associations. The haploblock containing rs9884090 is associated with reduced protein O-glycosyltransferase 1 (POGLUT1) expression (eQTL P<0.05), and functional annotation suggested a potential causative variant (rs71767581). This work implicates POGLUT1 in iTTP pathophysiology and suggests altered post-translational modification of its targets may influence disease susceptibility.

Effective treatment with rituximab for the maintenance of remission in frequently relapsing minimal change disease.

AIM: Treatment of frequently relapsing or steroid-dependent minimal change disease (MCD) in children and adults remains challenging. Glucocorticoids and/or other immunosuppressive agents are the mainstay of treatment, but patients often experience toxicity from prolonged exposure and may either become treatment dependent and/or resistant. Increasing evidence suggests that rituximab (RTX) can be a useful alternative to standard immunosuppression and allow withdrawal of maintenance immunosuppressants; however, data on optimal treatment regimens, long-term efficacy and safety are still limited. METHODS: We undertook a prospective study of RTX to allow immunosuppression minimization in 15 young adults with frequently relapsing or steroid-dependent, biopsy-proven MCD. All patients were in remission at the start of treatment and on a calcineurin inhibitor. Two doses of RTX (1 gr) were given 6 months apart. A subset of patients also received an additional dose 12 months later, in order to examine the benefit of re-treatment. Biochemical and clinical parameters were monitored over an extended follow-up period of up to 43 months. RESULTS: Median steroid-free survival after RTX was 25 months (range 4-34). Mean relapse frequency decreased from 2.60 ± 0.28 to 0.4 ± 0.19 (P < 0.001) after RTX. Seven relapses occurred, five of which (71%) when CD19 counts were greater than 100 µ. Immunoglobulin levels remained unchanged, and no major side effects were observed throughout the follow-up period. CONCLUSIONS: Rituximab therapy is effective at maintaining prolonged steroid-free remission and reducing relapse frequency in this group of patients. Our study lends further support for the role of RTX in the treatment of patients with frequently relapsing or steroid-dependent MCD.

Tenofovir-associated kidney toxicity in HIV-infected patients: a review of the evidence.

Tenofovir (TDF) is an effective and widely used treatment for both human immunodeficiency virus (HIV) and hepatitis B virus infection. Although studies suggest that TDF has a low overall toxicity profile and only a modest effect on estimated glomerular filtration rate, numerous case reports have since appeared in the literature describing TDF-associated renal tubular dysfunction, and this is now a significant source of HIV-related referrals to nephrologists. The main target of toxicity appears to be the proximal tubule, and in severe cases, patients can develop renal Fanconi syndrome. We review findings from recent studies in this area performed by ourselves and others and discuss our direct experience as practicing nephrologists. In particular, we discuss: (1) the nature and extent of TDF-associated kidney toxicity in the HIV-infected population, (2) potential underlying mechanisms of toxicity in the proximal tubule, (3) risk factors for developing tubular dysfunction, and (4) suggested strategies to monitor patients on TDF therapy.

The planar cell polarity gene Vangl2 is required for mammalian kidney-branching morphogenesis and glomerular maturation.

The planar cell polarity (PCP) pathway, incorporating non-canonical Wnt signalling, controls embryonic convergent (CE) extension, polarized cell division and ciliary orientation. It also limits diameters of differentiating renal tubules, with mutation of certain components of the pathway causing cystic kidneys. Mutations in mouse Vangl genes encoding core PCP proteins cause neural tube defects (NTDs) and Vangl2 mutations also impair branching of embryonic mouse lung airways. Embryonic metanephric kidneys also undergo branching morphogenesis and Vangl2 is known to be expressed in ureteric bud/collecting duct and metanephric mesenchymal/nephron lineages. These observations led us to investigate metanephroi in Vangl2 mutant mice, Loop-tail (Lp). Although ureteric bud formation is normal in Vangl2(Lp/Lp) embryos, subsequent in vivo and in vitro branching morphogenesis is impaired. Null mutant kidneys are short, consistent with a CE defect. Differentiating glomerular epithelia express several PCP genes (Vangl1/2, Celsr1, Scrib, Mpk1/2 and Fat4) and glomeruli in Vangl2(Lp/Lp) fetuses are smaller and contain less prominent capillary loops than wild-type littermates. Furthermore, Vangl2(Lp/+) kidneys had modest reduction in glomerular numbers postnatally. Vangl2(Lp/Lp) metanephroi contained occasional dilated tubules but no overt cystic phenotype. These data show for the first time that a PCP gene is required for normal morphogenesis of both the ureteric bud and metanephric mesenchyme-derived structures. It has long been recognized that certain individuals with NTDs are born with malformed kidneys, and recent studies have discovered VANGL mutations in some NTD patients. On the basis of our mutant mouse study, we suggest that PCP pathway mutations should be sought when NTD and renal malformation co-exist.

Subclinical tubular injury in HIV-infected individuals on antiretroviral therapy: a cross-sectional analysis.

BACKGROUND: Randomized control studies have not shown an association between treatment with tenofovir (TDF) and clinically significant kidney toxicity. However, multiple cases of renal tubular toxicity have been described in patients with HIV treated with TDF. It is unclear whether spot urine protein- or albumin-creatinine ratio is a sufficiently sensitive screening test to detect subclinical renal tubular toxicity in patients with HIV. STUDY DESIGN: Cross-sectional. SETTING & PARTICIPANTS: 99 patients with HIV with serum creatinine levels < 1.70 mg/dL and dipstick-negative proteinuria; 19 were antiretroviral treatment (ART) naive, 47 were on a TDF regimen, and 33 were on ART, but with no history of TDF exposure. PREDICTOR OR FACTOR: Exposure to TDF. OUTCOMES: Spot urine concentrations of retinol-binding protein (RBP; a low-molecular-weight protein normally reabsorbed by the proximal tubule), N-acetyl-beta-D-glucosaminidase (NAG; a proximal tubule lysosomal enzyme), albumin (A; a marker of glomerular disease), and protein (P; a standard clinical screening test for kidney pathological states) expressed as a ratio to creatinine (C; U(RBP/C), U(NAG/C), U(A/C), and U(P/C), respectively). RESULTS: There were no significant differences in median U(A/C) (ART-naive, 7.3 mg/g [range, 0-245.8 mg/g]; TDF, 9.0 mg/g [range, 0.1-184.1 mg/g]; and non-TDF, 10.5 mg/g [range, 2.6-261.6 mg/g]; P = 0.8). U(RBP/C) excretion was significantly higher in the TDF group (median, 214.2 microg/g [range, 26.8-17,454.5 microg/g]) than in the ART-naive group (92.5 microg/g [range, 21.3-3,969.0 microg/g]; P = 0.03); there was also a trend toward higher values than in the non-TDF group (111.6 microg/g [range, 31.0-6,136.3 microg/g]; P = 0.08). U(NAG/C) excretion was significantly higher in both the TDF (median, 394.7 micromol/h/g [range, 140.5-10,851.3 micromol/h/g]; P = 0.01) and non-TDF (406.8 micromol/h/g [range, 12.4-8,485.8 micromol/h/g]; P = 0.03) groups compared with the ART-naive group (218.6 micromol/h/g [range, 56.5-2,876.1 micromol/h/g]). U(P/C) was significantly higher in the TDF (median, 123.9 mg/g [range, 53.1-566.4 mg/g]) than the non-TDF group (97.3 mg/g [range, 0-451.3 mg/g]; P = 0.03). The proportion of patients with evidence of tubular dysfunction (increased U(RBP/C) and/or U(NAG/C)) was considerably higher than the proportion with an increase in U(A/C) or U(P/C) in all groups: for ART-naive, 52.6% vs 31.6% vs 25.0%; for TDF, 80.9% vs 29.8% vs 52.2%; and for non-TDF, 81.8% vs 39.4% vs 30.0%. The level of agreement among the different urinary test results was low. LIMITATIONS: Causality cannot be established from single measurements of urinary markers in a cross-sectional study. CONCLUSIONS: Patients with HIV had high rates of subclinical proteinuria, but neither U(P/C) nor U(A/C) is sufficiently sensitive alone to detect many of these cases. Patients using TDF have increased U(RBP/C) and U(P/C); the significance of this will need to be determined from longer-term outcome studies.

A critique of clinical guidelines for detection of individuals with chronic kidney disease.

Chronic kidney disease (CKD) and its association with cardiovascular mortality is increasingly regarded as a global public health problem. International efforts to combat this 'epidemic' have led to fundamental changes not only in the way we measure renal function but also how we classify and manage CKD. Clinical guidelines have established the use of estimated glomerular filtration rate (eGFR) and Kidney Disease Outcomes Quality Initiative classification of kidney disease as the cornerstones of CKD detection. The introduction of these guidelines in routine practice has had considerable impact on the large number of patients newly labelled with a chronic disease. However, it is far from clear that these patients with low GFR have intrinsic kidney disease and the vast majority will not develop end-stage renal failure. Furthermore, there is a lack of evidence that identification of low GFR can usefully be used to screen populations either for metabolic complications of kidney disease or cardiovascular risk.

Predictors of renal outcome in HIV-associated nephropathy.

BACKGROUND: Human immunodeficiency virus (HIV)-associated nephropathy (HIVAN) is an important cause of end-stage renal disease among African American patients. This study was performed to study the epidemiology of HIVAN in a predominantly black African population and the impact of highly active antiretroviral therapy and other factors on the development of end-stage renal disease. METHODS: We retrospectively identified all patients with HIVAN, defined by biopsy or strict clinical criteria, in 8 clinics in the United Kingdom. Baseline renal function, HIV parameters, renal pathological index of chronic damage, and responses to highly active antiretroviral therapy were analyzed, and factors associated with adverse renal outcome were identified. RESULTS: From 1998 through 2004, we studied 16,834 patients, 61 of whom had HIVAN. HIVAN prevalence in black patients was 0.93%, and HIVAN incidence in those without renal disease at baseline was 0.61 per 1000 person-years. After a median of 4.2 years, 34 patients (56%) had developed end-stage renal disease. There were no significant differences in renal function and HIV parameters at baseline, time to initiation of highly active antiretroviral therapy, and rates of HIV RNA suppression between the 20 patients who developed end-stage renal disease >3 months after receiving the HIVAN diagnosis and the 23 patients who maintained stable renal function. However, the index of chronic damage score was significantly higher in those who developed end-stage renal disease (P < .001), and an index of chronic damage score >75 was associated with shorter renal survival (P < .001). CONCLUSIONS: Whereas overall patient survival suggested an important benefit of highly active antiretroviral therapy, no additional renal benefit of early initiation of highly active antiretroviral therapy or viral suppression could be demonstrated in this large cohort of patients with established HIVAN. Severity of chronic kidney damage, as quantified by biopsy, was the strongest predictor of renal outcome.

Secondary amyloidosis in a needle phobic intra-venous drug user.

A case of acute-on-chronic renal failure is presented that is the sequela of secondary (AA) amyloidosis in a hepatitis positive intravenous drug user (IVDU) with chronic venous ulceration. The importance of groin examination is stressed when upper limb veins in a suspected IVDU are normal. Recent epidemiological data is discussed that suggests geographical location and the subcutaneous (SC) route of drug administration are both contributing factors to the development of AA amyloidosis and not chronic infection with HIV, HBV or HCV.

Hyper-IgG4 disease: report and characterisation of a new disease.

BACKGROUND: We highlight a chronic inflammatory disease we call 'hyper-IgG4 disease', which has many synonyms depending on the organ involved, the country of origin and the year of the report. It is characterized histologically by a lymphoplasmacytic inflammation with IgG4-positive cells and exuberant fibrosis, which leaves dense fibrosis on resolution. A typical example is idiopathic retroperitoneal fibrosis, but the initial report in 2001 was of sclerosing pancreatitis. METHODS: We report an index case with fever and severe systemic disease. We have also reviewed the histology of 11 further patients with idiopathic retroperitoneal fibrosis for evidence of IgG4-expressing plasma cells, and examined a wide range of other inflammatory conditions and fibrotic diseases as organ-specific controls. We have reviewed the published literature for disease associations with idiopathic, systemic fibrosing conditions and the synonyms: pseudotumour, myofibroblastic tumour, plasma cell granuloma, systemic fibrosis, xanthofibrogranulomatosis, and multifocal fibrosclerosis. RESULTS: Histology from all 12 patients showed, to varying degrees, fibrosis, intense inflammatory cell infiltration with lymphocytes, plasma cells, scattered neutrophils, and sometimes eosinophilic aggregates, with venulitis and obliterative arteritis. The majority of lymphocytes were T cells that expressed CD8 and CD4, with scattered B-cell-rich small lymphoid follicles. In all cases, there was a significant increase in IgG4-positive plasma cells compared with controls. In two cases, biopsies before and after steroid treatment were available, and only scattered plasma cells were seen after treatment, none of them expressing IgG4. Review of the literature shows that although pathology commonly appears confined to one organ, patients can have systemic symptoms and fever. In the active period, there is an acute phase response with a high serum concentration of IgG, and during this phase, there is a rapid clinical response to glucocorticoid steroid treatment. CONCLUSION: We believe that hyper-IgG4 disease is an important condition to recognise, as the diagnosis can be readily verified and the outcome with treatment is very good.

Renal outcome in adults with renal insufficiency and irregular asymmetric kidneys.

BACKGROUND: The commonest cause of end-stage renal failure (ESRF) in children and young adults is congenital malformation of the kidney and urinary tract. In this retrospective review, we examine whether progression to ESRF can be predicted and whether treatment with angiotensin converting enzyme inhibitors (ACEI) can delay or prevent this. METHODS: We reviewed 78 patients with asymmetric irregular kidneys as a consequence of either primary vesico-ureteric reflux or renal dysplasia (Group 1, n = 44), or abnormal bladder function (Group 2, n = 34). Patients (median age 24 years) had an estimated GFR (eGFR) < 60 ml/min/1.73 m2 with at least 5 years of follow up (median 143 months). 48 patients received ACEI. We explored potential prognostic factors that affect the time to ESRF using Cox-regression analyses. RESULTS: At start, mean (SE) creatinine was 189 (8) mumol/l, mean eGFR 41 (1) ml/min 1.73 m2, mean proteinuria 144 (14) mg/mmol creatinine (1.7 g/24 hrs). Of 78 patients, 36 (46%) developed ESRF, but none of 19 with proteinuria less than 50 mg/mmol and only two of 18 patients with eGFR above 50 ml/min did so. Renal outcome between Groups 1 and 2 appeared similar with no evidence for a difference. A benefit in favour of treatment with ACEI was observed above an eGFR of 40 ml/min (p = 0.024). CONCLUSION: The similar outcome of the two groups supports the nephrological nature of progressive renal failure in young men born with abnormal bladders. There is a watershed GFR of 40-50 ml/min at which ACEI treatment can be successful at improving renal outcome.

Rac regulates endothelial morphogenesis and capillary assembly.

Endothelial cells undergo branching morphogenesis to form capillary tubes. We have utilized an in vitro Matrigel overlay assay to analyze the role of the cytoskeleton and Rho GTPases during this process. The addition of matrix first induces changes in cell morphology characterized by the formation of dynamic cellular protrusions and the assembly of discrete aggregates or cords of aligned cells resembling primitive capillary-like structures, but without a recognizable lumen. This is followed by cell migration leading to the formation of a complex interconnecting network of capillary tubes with readily identifiable lumens. Inhibition of actin polymerization or actin-myosin contraction inhibits cell migration but has no effect on the initial changes in endothelial cell morphology. However, inhibition of microtubule dynamics prevents both the initial cell shape changes as well as cell migration. We find that the small GTPase Rac is essential for the matrix-induced changes in endothelial cell morphology, whereas p21-activated kinase, an effector of Rac, is required for cell motility. We conclude that Rac integrates signaling through both the actin and microtubule cytoskeletons to promote capillary tube assembly.