Emma Ashton

Genetic testing in renal disease.

A revolution is happening in genetics! The decoding of the first genome in 2003 was a large international collaborative effort that took about 13xa0years at a cost of around

Genetic testing in children with surfactant dysfunction

2.7 billion. Now, only a few years later, new technology allows the sequencing of an entire genome within a few weeks—and at a cost of less than

Clinical and molecular aspects of distal renal tubular acidosis in children

10,000. The vaunted

Clinico-pathological correlations of congenital and infantile nephrotic syndrome over twenty years.

1000 genome is within reach. These extraordinary advances will undoubtedly transform the way we practice medicine. But, like any new technology, it carries risks, as well as benefits. As physicians, we need to understand the implications in order to best utilise these advances for our patients and to provide informed advice. In this review, our aim is to explain these new technologies, to separate the hype from the reality and to address some of the resulting questions and implications. The practical objective is to provide a simple overview of the available technologies and of purpose to which they are best suited.

Clinical impact of a targeted next-generation sequencing gene panel for autoinflammation and vasculitis

Objectives To present the UK experience in genetic diagnoses of surfactant protein dysfunction disorders and develop a referral algorithm for neonates and children with persistent respiratory problems. Materials and methods Between 2006 and 2011, 427 cases were referred for surfactant mutation analyses to the North East Thames Regional Molecular Genetics Laboratory at Great Ormond Street Hospital, London. The results were reviewed and referring physicians of mutation positive cases contacted to complete a questionnaire providing clinical, radiological, histological and outcome information. Results 25 new cases were found to have genetic mutations for surfactant dysfunction disorders (7.5%), with six resulting in surfactant protein B dysfunction, seven surfactant protein C dysfunction and 12 ATP-binding cassette subfamily A member 3 (ABCA3) dysfunction. The referrals were from 15 different paediatric centres. In addition, three affected surfactant protein B (SFTPB) cases were prenatal diagnoses, following the birth of previously affected children. The majority of the confirmed cases (23 of 25) were born after 37u2005weeks gestation. All children with SFTPB dysfunction and the majority of ABCA3 patients presented with respiratory distress at birth. All SFTPB cases died from intractable respiratory failure. The outcome for ABCA3 mutations was variable with seven survivors. The clinical and radiological presentation of surfactant protein C (SFTPC) patients suggested mainly interstitial lung process with the majority surviving on medication. Conclusions Surfactant mutation analysis is now well established in the UK and allows better genetic diagnosis and counselling. The rarity of the condition makes it difficult to develop a validated algorithm for genetic evaluation with a need for international networking. Referrals need to be rationalised for the service to be time and cost effective.

Acidosis and Deafness in Patients with Recessive Mutations in FOXI1

BackgroundDistal renal tubular acidosis (dRTA) is characterized by hyperchloraemic metabolic acidosis, hypokalaemia, hypercalciuria and nephrocalcinosis. It is due to reduced urinary acidification by the α-intercalated cells in the collecting duct and can be caused by mutations in genes that encode subunits of the vacuolar H+-ATPase (ATP6V1B1, ATP6V0A4) or the anion exchanger 1 (SLC4A1). Treatment with alkali is the mainstay of therapy.MethodsThis study is an analysis of clinical data from a long-term follow-up of 24 children with dRTA in a single centre, including a genetic analysis.ResultsOf the 24 children included in the study, genetic diagnosis was confirmed in 19 patients, with six children having mutations in ATP6V1B1, ten in ATP6V0A4 and three in SLC4A1; molecular diagnosis was not available for five children. Five novel mutations were detected (2 in ATP6V1B1 and 3 in ATP6V0A4). Two-thirds of patients presented with features of proximal tubular dysfunction leading to an erroneous diagnosis of renal Fanconi syndrome. The proximal tubulopathy disappeared after resolution of acidosis, indicating the importance of following proximal tubular function to establish the correct diagnosis. Growth retardation with a height below −2 standard deviation score was found in ten patients at presentation, but persisted in only three of these children once established on alkali treatment. Sensorineural hearing loss was found in five of the six patients with an ATP6V1B1 mutation. Only one patient with an ATP6V0A4 mutation had sensorineural hearing loss during childhood. Nine children developed medullary cysts, but without apparent clinical consequences. Cyst development in this cohort was not correlated with age at therapy onset, molecular diagnosis, growth parameters or renal function.ConclusionIn general, the prognosis of dRTA is good in children treated with alkali.

Renal apnoea: extreme disturbance of homoeostasis in a child with Bartter syndrome type IV

BackgroundNephrotic syndrome (NS) presenting early in life is caused by heterogeneous glomerular diseases. We retrospectively evaluated whether histological diagnosis in children presenting with NS in the first year of life predicts remission or progression to end-stage kidney disease (ESKD).MethodsThis is a single centre retrospective review of all children diagnosed with NS before one year of age between 1990 and 2009. All subjects had a renal biopsy, which was independently blindly reviewed by a single renal pathologist for the purpose of this study.ResultsForty-nine children (25 female) who presented at 0.1–11.6 (median 1.6) months were included with 31 presenting within the first three months of life. Histopathological review diagnostic categories were; 13 Mesangial proliferative glomerulopathy (MesGN), 12 Focal and segmental glomerulosclerosis (FSGS), 11 Finnish type changes, eight Diffuse Mesangial Sclerosis (DMS), three Minimal change disease (MCD) and one each of Dense Deposit Disease (DDD) and Membranous nephropathy. Two children died from haemorrhagic complications of the biopsy. Eight children achieved remission (four MesGN, one Finnish type changes, one FSGS, one MCD and one membranous) with patient and renal survival of 73xa0% and 43xa0%, respectively, at follow-up duration of 5–222 (median 73) months (with five lost to follow-up). All children with Finnish-type histopathological changes presented within five months of age. Due to the historical nature of the cohort, genetic testing was only available for 14 children, nine of whom had an identifiable genetic basis (seven NPHS1, one PLCE1 and one ITGA3) with none of these nine children achieving remission. All of them had presented within four months of age and required renal replacement therapy, and two died.ConclusionsHistopathological findings are varied in children presenting with NS early in life. Whilst groups of histological patterns of disease are associated with differing outcomes, accurate prediction of disease course in a specific case is difficult and more widespread genetic testing may improve the understanding of this group of diseases and their optimal management

Potential and pitfalls in the genetic diagnosis of kidney diseases

Background Monogenic autoinflammatory diseases (AID) are a rapidly expanding group of genetically diverse but phenotypically overlapping systemic inflammatory disorders associated with dysregulated innate immunity. They cause significant morbidity, mortality and economic burden. Here, we aimed to develop and evaluate the clinical impact of a NGS targeted gene panel, the “Vasculitis and Inflammation Panel” (VIP) for AID and vasculitis. Methods The Agilent SureDesign tool was used to design 2 versions of VIP; VIP1 targeting 113 genes, and a later version, VIP2, targeting 166 genes. Captured and indexed libraries (QXT Target Enrichment System) prepared for 72 patients were sequenced as a multiplex of 16 samples on an Illumina MiSeq sequencer in 150bp paired-end mode. The cohort comprised 22 positive control DNA samples from patients with previously validated mutations in a variety of the genes; and 50 prospective samples from patients with suspected AID in whom previous Sanger based genetic screening had been non-diagnostic. Results VIP was sensitive and specific at detecting all the different types of known mutations in 22 positive controls, including gene deletion, small INDELS, and somatic mosaicism with allele fraction as low as 3%. Six/50 patients (12%) with unclassified AID had at least one class 5 (clearly pathogenic) variant; and 11/50 (22%) had at least one likely pathogenic variant (class 4). Overall, testing with VIP resulted in a firm or strongly suspected molecular diagnosis in 16/50 patients (32%). Conclusions The high diagnostic yield and accuracy of this comprehensive targeted gene panel validate the use of broad NGS-based testing for patients with suspected AID.

Simultaneous sequencing of 37 genes identified causative mutations in the majority of children with renal tubulopathies

Maintenance of the composition of inner ear fluid and regulation of electrolytes and acid-base homeostasis in the collecting duct system of the kidney require an overlapping set of membrane transport proteins regulated by the forkhead transcription factor FOXI1. In two unrelated consanguineous families, we identified three patients with novel homozygous missense mutations in FOXI1 (p.L146F and p.R213P) predicted to affect the highly conserved DNA binding domain. Patients presented with early-onset sensorineural deafness and distal renal tubular acidosis. In cultured cells, the mutations reduced the DNA binding affinity of FOXI1, which hence, failed to adequately activate genes crucial for normal inner ear function and acid-base regulation in the kidney. A substantial proportion of patients with a clinical diagnosis of inherited distal renal tubular acidosis has no identified causative mutations in currently known disease genes. Our data suggest that recessive mutations in FOXI1 can explain the disease in a subset of these patients.

Clinical and diagnostic features of Bartter and Gitelman syndromes

A 2-week-old girl was transferred to our renal ward in February, 2014, from the neonatal intensive care unit of her local hospital with polyuria (200 mL/kg per day) and extreme acid–base and electrolyte disturbance that had been present from birth. She was born by spontaneous delivery at 32 weeks gestation, after a pregnancy complicated by severe polyhydramnios necessitating two amnioreductions that had removed more than 6 L of fluid. She is the third child of consanguineous parents, with no relevant family history.