Corrigendum to "An Artificial Intelligence Generated Automated Algorithm to Measure Total Kidney Volume in ADPKD" [Kidney International Reports Volume 9, Issue 2, February 2024, Pages 249-256].

[This corrects the article DOI: 10.1016/j.ekir.2023.10.029.].

An Artificial Intelligence Generated Automated Algorithm to Measure Total Kidney Volume in ADPKD.

Introduction: Accurate tools to inform individual prognosis in patients with autosomal dominant polycystic kidney disease (ADPKD) are lacking. Here, we report an artificial intelligence (AI)-generated method for routinely measuring total kidney volume (TKV). Methods: An ensemble U-net algorithm was created using the nnUNet approach. The training and internal cross-validation cohort consisted of all 1.5T magnetic resonance imaging (MRI) data acquired using 5 different MRI scanners (454 kidneys, 227 scans) in the CYSTic consortium, which was first manually segmented by a single human operator. As an independent validation cohort, we utilized 48 sequential clinical MRI scans with reference results of manual segmentation acquired by 6 individual analysts at a single center. The tool was then implemented for clinical use and its performance analyzed. Results: The training or internal validation cohort was younger (mean age 44.0 vs. 51.5 years) and the female-to-male ratio higher (1.2 vs. 0.94) compared to the clinical validation cohort. The majority of CYSTic patients had PKD1 mutations (79%) and typical disease (Mayo Imaging class 1, 86%). The median DICE score on the clinical validation data set between the algorithm and human analysts was 0.96 for left and right kidneys with a median TKV error of -1.8%. The time taken to manually segment kidneys in the CYSTic data set was 56 (±28) minutes, whereas manual corrections of the algorithm output took 8.5 (±9.2) minutes per scan. Conclusion: Our AI-based algorithm demonstrates performance comparable to manual segmentation. Its rapidity and precision in real-world clinical cases demonstrate its suitability for clinical application.

Combining genotype with height-adjusted kidney length predicts rapid progression of ADPKD.

INTRODUCTION: Our main objective was to identify baseline prognostic factors predictive of rapid disease progression in a large unselected clinical autosomal dominant polycystic kidney disease (ADPKD) cohort. METHODS: A cross-sectional analysis was performed in 618 consecutive ADPKD patients assessed and followed-up for over a decade. A total of 123 patients (19.9%) had reached kidney failure by the study date. Data were available for the following: baseline eGFR (n = 501), genotype (n = 549), baseline ultrasound mean kidney length (MKL, n = 424) and height-adjusted baseline MKL (HtMKL, n = 377). Rapid disease progression was defined as an annualized eGFR decline (∆eGFR) of >2.5 mL/min/year by linear regression over 5 years (n = 158). Patients were further divided into slow, rapid and very rapid ∆eGFR classes for analysis. Genotyped patients were classified into several categories: PKD1 (T, truncating; or NT, non-truncating), PKD2, other genes (non-PKD1 or -PKD2), no mutation detected or variants of uncertain significance. RESULTS: A PKD1-T genotype had the strongest influence on the probability of reduced baseline kidney function by age. A multivariate logistic regression model identified PKD1-T genotype and HtMKL (>9.5 cm/m) as independent predictors for rapid disease progression. The combination of both factors increased the positive predictive value for rapid disease progression over age 40 years and of reaching kidney failure by age 60 years to 100%. Exploratory analysis in a subgroup with available total kidney volumes showed higher positive predictive value (100% vs 80%) and negative predictive value (42% vs 33%) in predicting rapid disease progression compared with the Mayo Imaging Classification (1C-E). CONCLUSION: Real-world longitudinal data confirm the importance of genotype and kidney length as independent variables determining ∆eGFR. Individuals with the highest risk of rapid disease progression can be positively selected for treatment based on this combination.

Individualized everolimus treatment for tuberous sclerosis-related angiomyolipoma promotes treatment adherence and response.

Background: Everolimus is a potential alternative to embolization and nephrectomy for managing tuberous sclerosis complex (TSC)-associated renal angiomyolipoma (AML). In 2016, National Health Service England approved its use through regional centres for renal AML ≥30 mm showing interval growth. Evidence of lesion stabilization or reduction after 6 months is mandated for continuation of long-term treatment. Methods: From November 2016 to June 2021, all potentially eligible adult TSC patients with AML across Yorkshire and Humber were referred for assessment and monitoring. Eligible patients underwent baseline renal magnetic resonance imaging (MRI) assessment and a follow-up MRI scan after 6 months on everolimus. Dose titration was guided by trough levels and lesion responsiveness using a new 3D MRI volumetric protocol. Results: Of 28 patients commencing treatment, 19 tolerated everolimus for >3 months. Overall, 11 patients (40%) discontinued treatment, mostly due to recurrent infections (42%) and allergic reactions (25%). Sixty-eight percent required dose adjustments from the initiating dose (10 mg) due to sub-optimal trough levels (38%), minimal AML response (15%) or adverse events (47%). 3D volumetric assessment confirmed a reduction in AML volume of a pre-selected index lesion in all treatment-naïve cases (n = 14), showing superiority over 2D measurements of lesion diameter. Conclusion: In this cohort, everolimus promoted AML regression in all patients who tolerated the drug for >6 months with stabilization observed over 3 years. Trough levels enabled individual dose titration to maximize responsiveness and minimize side effects. The use of 3D MRI assessment of lesion volume was superior to 2D measurements of lesion diameter in monitoring treatment response.

Research priorities for autosomal dominant polycystic kidney disease: a UK priority setting partnership.

OBJECTIVES: Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney condition, accounting for 7%-10% of patients with kidney failure. Fundamental basic science and clinical research on ADPKD is underway worldwide but no one has yet considered which areas should be prioritised to maximise returns from limited future funding. The Polycystic Kidney Disease Charity began a priority setting partnership with the James Lind Alliance (JLA) in the UK in 2019-2020 to identify areas of uncertainty in the ADPKD care pathway and allow patients, carers and healthcare professionals to rank the 10 most important questions for research. DESIGN: The scope covered ADPKD diagnosis and management, identifying new treatments to prevent/slow disease progression and practical, integrated patient support (https://pkdcharity.org.uk/research/for-researchers/adpkd-research-priorities). We used adapted JLA methodology. Initially, an independent information specialist collated uncertainties in ADPKD care from recent consensus conference proceedings and additional literature. These were refined into indicative questions with Steering Group oversight. Finally, the 10 most important questions were established via a survey and online consensus workshop. SETTING: UK. PARTICIPANTS: 747 survey respondents (76% patients, 13% carers, 11% healthcare professionals); 23 workshop attendees. RESULTS: 117 uncertainties in ADPKD care were identified and refined into 35 indicative questions. A shortlist of 17 questions was established through the survey. Workshop participants reached agreement on the top 10 ranking. The top three questions prioritised by patients, carers and healthcare professionals centred around slowing disease progression, identifying persons for early treatment and organising care to improve outcomes. CONCLUSIONS: Our shortlist reflects the varied physical, psychological and practical challenges of living with and treating ADPKD, and perceived gaps in knowledge that impair optimal care. We propose that future ADPKD research funding takes these priorities into account to focus on the most important areas and to maximise improvements in ADPKD outcomes.

Flank pain has a significant adverse impact on quality of life in ADPKD: the CYSTic-QoL study.

Background: Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disorder and a major cause of kidney failure worldwide. However, its impact on quality-of-life has not been systematically explored. Methods: The CYSTic-QoL study was an observational study designed to study quality-of-life in adult European ADPKD patients with an estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73 m2. A total of 465 patients were recruited from six expert European centres with baseline data recorded, including health-related quality-of-life (HRQoL), incorporating a Kidney Disease QoL short form questionnaire (KDQoL-SF, version 1.3), magnetic resonance imaging (MRI) for total kidney volume (TKV) measurements and DNA for genotyping. The cohort was stratified by baseline eGFR, TKV or genotype and correlated with HRQoL scores. Bivariate and multivariate analyses were applied to examine the relationship between HRQoL and variables of interest. KDQoL-SF scores were calculated using an online tool provided by the RAND organization. For 36-item short form values, mean centre scores were normalized to their native populations. Results: The mean age of participants was 43 years and 55% were female, with a mean eGFR of 77 mL/min/1.73 m2 and height-adjusted TKV (ht-TKV) of 849 mL/min; 66% had PKD1 pathogenic variants. ADPKD patients uniformly reported decreased general health and less energy, with the majority also experiencing poorer physical, mental or emotional health and limitations in social functioning. A total of 32.5% of participants experienced flank pain, which was significantly and negatively correlated with the majority of KDQoL-SF subscales by multivariate analysis. Higher ht-TKV and lower eGFR were negatively associated with decreased energy and poorer physical health, respectively, although not with flank pain. Conclusion: ADPKD patients suffer from significantly decreased QoL in multiple domains, exacerbated particularly by chronic pain.

Global microRNA profiling in human urinary exosomes reveals novel disease biomarkers and cellular pathways for autosomal dominant polycystic kidney disease.

MicroRNAs (miRNAs) play an important role in regulating gene expression in health and disease but their role in modifying disease expression in Autosomal Dominant Polycystic Kidney Disease (ADPKD) remains uncertain. Here, we profiled human urinary exosome miRNA by global small RNA-sequencing in an initial discovery cohort of seven patients with ADPKD with early disease (eGFR over 60ml/min/1.73m2), nine with late disease (eGFR under 60ml/min/1.73m2), and compared their differential expression with six age and sex matched healthy controls. Two kidney-enriched candidate miRNA families were identified (miR-192/miR-194-2 and miR-30) and selected for confirmatory testing in a 60 patient validation cohort by quantitative polymerase chain reaction. We confirmed that miR-192-5p, miR-194-5p, miR-30a-5p, miR-30d-5p and miR-30e-5p were significantly downregulated in patient urine exosomes, in murine Pkd1 cystic kidneys and in human PKD1 cystic kidney tissue. All five miRNAs showed significant correlations with baseline eGFR and ultrasound-determined mean kidney length and improved the diagnostic performance (area under the curve) of mean kidney length for the rate of disease progression. Finally, inverse correlations of these two miRNA families with increased expression in their predicted target genes in patient PKD1 cystic tissue identified dysregulated pathways and transcriptional networks including novel interactions between miR-194-5p and two potentially relevant candidate genes, PIK3R1 and ANO1. Thus, our results identify a subset of urinary exosomal miRNAs that could serve as novel biomarkers of disease progression and suggest new therapeutic targets in ADPKD.

A rapid high-performance semi-automated tool to measure total kidney volume from MRI in autosomal dominant polycystic kidney disease.

OBJECTIVES: To develop a high-performance, rapid semi-automated method (Sheffield TKV Tool) for measuring total kidney volume (TKV) from magnetic resonance images (MRI) in patients with autosomal dominant polycystic kidney disease (ADPKD). METHODS: TKV was initially measured in 61 patients with ADPKD using the Sheffield TKV Tool and its performance compared to manual segmentation and other published methods (ellipsoidal, mid-slice, MIROS). It was then validated using an external dataset of MRI scans from 65 patients with ADPKD. RESULTS: Sixty-one patients (mean age 45 ± 14 years, baseline eGFR 76 ± 32 ml/min/1.73 m2) with ADPKD had a wide range of TKV (258-3680 ml) measured manually. The Sheffield TKV Tool was highly accurate (mean volume error 0.5 ± 5.3% for right kidney, - 0.7 ± 5.5% for left kidney), reproducible (intra-operator variability - 0.2 ± 1.3%; inter-operator variability 1.1 ± 2.9%) and outperformed published methods. It took less than 6 min to execute and performed consistently with high accuracy in an external MRI dataset of T2-weighted sequences with TKV acquired using three different scanners and measured using a different segmentation methodology (mean volume error was 3.45 ± 3.96%, n = 65). CONCLUSIONS: The Sheffield TKV Tool is operator friendly, requiring minimal user interaction to rapidly, accurately and reproducibly measure TKV in this, the largest reported unselected European patient cohort with ADPKD. It is more accurate than estimating equations and its accuracy is maintained at larger kidney volumes than previously reported with other semi-automated methods. It is free to use, can run as an independent executable and will accelerate the application of TKV as a prognostic biomarker for ADPKD into clinical practice. KEY POINTS: • This new semi-automated method (Sheffield TKV Tool) to measure total kidney volume (TKV) will facilitate the routine clinical assessment of patients with ADPKD. • Measuring TKV manually is time consuming and laborious. • TKV is a prognostic indicator in ADPKD and the only imaging biomarker approved by the FDA and EMA.

Magnetic resonance imaging biomarkers for chronic kidney disease: a position paper from the European Cooperation in Science and Technology Action PARENCHIMA.

Functional renal magnetic resonance imaging (MRI) has seen a number of recent advances, and techniques are now available that can generate quantitative imaging biomarkers with the potential to improve the management of kidney disease. Such biomarkers are sensitive to changes in renal blood flow, tissue perfusion, oxygenation and microstructure (including inflammation and fibrosis), processes that are important in a range of renal diseases including chronic kidney disease. However, several challenges remain to move these techniques towards clinical adoption, from technical validation through biological and clinical validation, to demonstration of cost-effectiveness and regulatory qualification. To address these challenges, the European Cooperation in Science and Technology Action PARENCHIMA was initiated in early 2017. PARENCHIMA is a multidisciplinary pan-European network with an overarching aim of eliminating the main barriers to the broader evaluation, commercial exploitation and clinical use of renal MRI biomarkers. This position paper lays out PARENCHIMA's vision on key clinical questions that MRI must address to become more widely used in patients with kidney disease, first within research settings and ultimately in clinical practice. We then present a series of practical recommendations to accelerate the study and translation of these techniques.

Parallel microarray profiling identifies ErbB4 as a determinant of cyst growth in ADPKD and a prognostic biomarker for disease progression.

Autosomal dominant polycystic kidney disease (ADPKD) is the fourth most common cause of end-stage renal disease. The disease course can be highly variable and treatment options are limited. To identify new therapeutic targets and prognostic biomarkers of disease, we conducted parallel discovery microarray profiling in normal and diseased human PKD1 cystic kidney cells. A total of 1,515 genes and 5 miRNA were differentially expressed by more than twofold in PKD1 cells. Functional enrichment analysis identified 30 dysregulated signaling pathways including the epidermal growth factor (EGF) receptor pathway. In this paper, we report that the EGF/ErbB family receptor ErbB4 is a major factor driving cyst growth in ADPKD. Expression of ErbB4 in vivo was increased in human ADPKD and Pkd1 cystic kidneys, both transcriptionally and posttranscriptionally by mir-193b-3p. Ligand-induced activation of ErbB4 drives cystic proliferation and expansion suggesting a pathogenic role in cystogenesis. Our results implicate ErbB4 activation as functionally relevant in ADPKD, both as a marker of disease activity and as a new therapeutic target in this major kidney disease.

Increased psychosocial risk, depression and reduced quality of life living with autosomal dominant polycystic kidney disease.

BACKGROUND: The psychosocial impact of living with autosomal dominant polycystic kidney disease (ADPKD) is poorly understood. In this study, we assessed the overall quality of life (QOL), mood, perceived social support and psychosocial risk of having a diagnosis of ADPKD in a patient cohort from a major UK nephrology centre serving a large catchment population. METHODS: A postal questionnaire was sent to 349 patients registered at the Sheffield Kidney Institute with chronic kidney disease but not on renal replacement therapy (RRT). The questionnaire incorporated three validated forms: kidney disease quality-of-life short form (KDQOL SF1.3) to assess QOL; nine-item patient health questionnaire (PHQ9) to screen for depression; multidimensional scale of perceived social support (MSPSS) to evaluate perceived social support; as well as a novel genetic psychosocial risk instrument (GPRI-ADPKD) designed to study the specific psychosocial impact of coping with a diagnosis of ADPKD. RESULTS: The overall response rate was 53%. Patients with a lower estimated glomerular filtration rate (<30 mL/min) or larger kidneys (mean length on ultrasound ≥17 cm) reported reduced QOL and increased psychosocial risk. Clinically significant depression was reported in 22% and 62% felt guilty about passing ADPKD on to their children. In multivariate analysis, female gender was associated with overall poorer psychosocial well-being, whereas increasing age, lower kidney function, larger kidneys and loss of a first degree relative from ADPKD were additional risk factors for QOL, depression or psychosocial risk, respectively. CONCLUSIONS: Our results reveal a significantly poorer QOL and increasing psychosocial risk with markers of disease progression in patients, particularly women, with ADPKD prior to starting RRT. The future management strategy of ADPKD should address these issues and provide for better individual and family support throughout the patient journey.

Genetic testing in the assessment of living related kidney donors at risk of autosomal dominant polycystic kidney disease.

BACKGROUND: Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic cause of renal failure. In most patients who develop end-stage renal disease, transplantation is the renal replacement modality of choice. For living related kidney donation (LRKD), the major challenge is to exclude the diagnosis of ADPKD in potential donors. Renal imaging may not exclude ADPKD particularly in younger donors and molecular genetic testing is advised. We report the largest series to date evaluating the role of genetic testing for ADPKD in LRKD assessment. METHODS: A cohort of patients with ADPKD and potential LRKD were referred for genetic testing for ADPKD between April 2010 and October 2012. DNA sequencing of PKD1 and PKD2 was performed. Imaging investigations and transplant outcomes after genetic testing were collected. RESULTS: Nineteen patients and 25 potential LRKD underwent genetic testing. Of potential LRKD, one tested positive for ADPKD and one with a diagnostic ultrasound tested negative. Despite negative genetic testing, two potential LRKD were considered unsuitable because of the detection of stage I ("simple") renal cysts on computed tomography. Four living related kidney transplants have occurred, and two are planned. Three patients subsequently refused the donation as the potential donor was a child. CONCLUSION: Predictive genetic testing can facilitate donor evaluation and augment living related kidney transplantation in ADPKD. Psychologic challenges associated with accepting an LRKD require careful consideration during recipient assessment. The acceptability of using a kidney with cysts from a mutation-negative donor should be evaluated by a multidisciplinary team.

How simple are 'simple renal cysts'?

The increasing use of medical imaging as an investigative tool is leading to the incidental and frequent finding of renal cysts in the general population. The presence of a solitary or multiple renal cysts has been generally considered benign in the absence of a family history of renal cystic disease or evidence of chronic kidney disease. Nonetheless, a number of recent studies have questioned this consensus by reported associations with the development of hypertension or malignant change. For these reasons, some clinicians consider the presence of renal cysts to be a contraindication to kidney donation. The situation is complicated by the different usage of the term 'simple' by some radiologists (to indicate non-complex lesions) or nephrologists (to indicate age-related non-hereditary lesions). We propose that the term 'simple' be replaced with the morphological description, Stage I renal cyst (Bosniak Classification). The presence of a Stage I renal cyst should not preclude kidney donation. However, occult renal disease should be excluded and appropriate donor assessment performed.

Epidemiology of patients in England and Wales with autosomal dominant polycystic kidney disease and end-stage renal failure.

BACKGROUND: Autosomal dominant polycystic kidney disease (ADPKD) is the leading genetic cause of end-stage renal failure (ESRF). The epidemiology of the incident ADPKD patient cohort requiring renal replacement therapy (RRT) in England and Wales has not been described. METHODS: We used a retrospective cohort design. Incident adult patients commencing RRT between 1 January 2000 and 31 December 2011 in England and Wales were identified from the UK Renal Registry. Patients were stratified into three groups based on primary renal diagnosis (PRD): (i) ADPKD, (ii) diabetes as PRD, (iii) individuals with another PRD ('other'). Baseline demographics, comorbidity, care-related measures and outcomes including patient survival are described. RESULTS: A total of 52,608 individuals started RRT during the study period, 3598 (6.8%) had ADPKD, 12,137 (23.1%) diabetes as PRD and 36,873 had another PRD diagnosis. The median age of commencing RRT was 55 years in the ADPKD group compared with 62 and 66 years in those with diabetes or 'other' PRD, respectively. The median age of starting RRT did not change within the ADPKD group over the 10-year period. Median age at death was similar across all groups. The ADPKD group had a lower hazard for all-cause mortality compared with the 'other' PRD group (adjusted hazard ratio 0.45, 95% CI 0.38-0.53). In all PRD groups, crude mortality rates had improved between 2000-06 and 2007-11. CONCLUSION: Although engaged in renal services earlier than some other patient groups, individuals with ADPKD start RRT at a younger age and this has remained unchanged over the last decade. Developing a nationwide cohort and an enhanced disease-specific dataset would facilitate a wide range of research and quality improvement initiatives to try to modify progression to ESRF and the course of RRT.

The challenges and surprises of a definitive molecular genetic diagnosis.

Making precise molecular genetic diagnoses in inherited kidney diseases is important. Gee et al. describe families with end-stage renal disease secondary to a presumed diagnosis of a nephronophthisis-related ciliopathy (NPHP-RC), in whom a combination of approaches allowed genetic diagnoses to be made. New genetic approaches to the diagnosis of childhood renal failure are becoming mainstream and will hopefully improve patient management, avoid clinical misdiagnoses, reduce the need for invasive investigations, and allow screening of at-risk relatives.

Functional modelling of a novel mutation in BBS5.

BACKGROUND: Bardet-Biedl syndrome (BBS) is an autosomal recessive ciliopathy disorder with 18 known causative genes (BBS1-18). The primary clinical features are renal abnormalities, rod-cone dystrophy, post-axial polydactyly, learning difficulties, obesity and male hypogonadism. RESULTS: We describe the clinical phenotype in three Saudi siblings in whom we have identified a novel mutation in exon 12 of BBS5 (c.966dupT; p.Ala323CysfsX57). This single nucleotide duplication creates a frame shift results in a predicted elongated peptide. Translation blocking Morpholino oligonucleotides were used to create zebrafish bbs5 morphants. Morphants displayed retinal layering defects, abnormal cardiac looping and dilated, cystic pronephric ducts with reduced cilia expression. Morphants also displayed significantly reduced dextran clearance via the pronephros compared to wildtype embryos, suggesting reduced renal function in morphants. The eye, kidney and heart defects reported in morphant zebrafish resemble the human phenotype of BBS5 mutations. The pathogenicity of the novel BBS5 mutation was determined. Mutant mRNA was unable to rescue pleiotropic phenotypes of bbs5 morphant zebrafish and in cell culture we demonstrate a mislocalisation of mutant BBS5 protein which fails to localise discretely with the basal body. CONCLUSIONS: We conclude that this novel BBS5 mutation has a deleterious function that accounts for the multisystem ciliopathy phenotype seen in affected human patients.

Investigating embryonic expression patterns and evolution of AHI1 and CEP290 genes, implicated in Joubert syndrome.

Joubert syndrome and related diseases (JSRD) are developmental cerebello-oculo-renal syndromes with phenotypes including cerebellar hypoplasia, retinal dystrophy and nephronophthisis (a cystic kidney disease). We have utilised the MRC-Wellcome Trust Human Developmental Biology Resource (HDBR), to perform in-situ hybridisation studies on embryonic tissues, revealing an early onset neuronal, retinal and renal expression pattern for AHI1. An almost identical pattern of expression is seen with CEP290 in human embryonic and fetal tissue. A novel finding is that both AHI1 and CEP290 demonstrate strong expression within the developing choroid plexus, a ciliated structure important for central nervous system development. To test if AHI1 and CEP290 may have co-evolved, we carried out a genomic survey of a large group of organisms across eukaryotic evolution. We found that, in animals, ahi1 and cep290 are almost always found together; however in other organisms either one may be found independent of the other. Finally, we tested in murine epithelial cells if Ahi1 was required for recruitment of Cep290 to the centrosome. We found no obvious differences in Cep290 localisation in the presence or absence of Ahi1, suggesting that, while Ahi1 and Cep290 may function together in the whole organism, they are not interdependent for localisation within a single cell. Taken together these data support a role for AHI1 and CEP290 in multiple organs throughout development and we suggest that this accounts for the wide phenotypic spectrum of AHI1 and CEP290 mutations in man.

Modelling a ciliopathy: Ahi1 knockdown in model systems reveals an essential role in brain, retinal, and renal development.

Joubert syndrome and related diseases (JSRD) are cerebello-oculo-renal syndromes with phenotypes including cerebellar hypoplasia, retinal dystrophy, and nephronophthisis (a cystic kidney disease). Mutations in AHI1 are the most common genetic cause of JSRD, with developmental hindbrain anomalies and retinal degeneration being prominent features. We demonstrate that Ahi1, a WD40 domain-containing protein, is highly conserved throughout evolution and its expression associates with ciliated organisms. In zebrafish ahi1 morphants, the phenotypic spectrum of JSRD is modeled, with embryos showing brain, eye, and ear abnormalities, together with renal cysts and cloacal dilatation. Following ahi1 knockdown in zebrafish, we demonstrate loss of cilia at Kupffer's vesicle and subsequently defects in cardiac left-right asymmetry. Finally, using siRNA in renal epithelial cells we demonstrate a role for Ahi1 in both ciliogenesis and cell-cell junction formation. These data support a role for Ahi1 in epithelial cell organization and ciliary formation and explain the ciliopathy phenotype of AHI1 mutations in man.

A meckelin-filamin A interaction mediates ciliogenesis.

MKS3, encoding the transmembrane receptor meckelin, is mutated in Meckel-Gruber syndrome (MKS), an autosomal-recessive ciliopathy. Meckelin localizes to the primary cilium, basal body and elsewhere within the cell. Here, we found that the cytoplasmic domain of meckelin directly interacts with the actin-binding protein filamin A, potentially at the apical cell surface associated with the basal body. Mutations in FLNA, the gene for filamin A, cause periventricular heterotopias. We identified a single consanguineous patient with an MKS-like ciliopathy that presented with both MKS and cerebellar heterotopia, caused by an unusual in-frame deletion mutation in the meckelin C-terminus at the region of interaction with filamin A. We modelled this mutation and found it to abrogate the meckelin-filamin A interaction. Furthermore, we found that loss of filamin A by siRNA knockdown, in patient cells, and in tissues from Flna(Dilp2) null mouse embryos results in cellular phenotypes identical to those caused by meckelin loss, namely basal body positioning and ciliogenesis defects. In addition, morpholino knockdown of flna in zebrafish embryos significantly increases the frequency of dysmorphology and severity of ciliopathy developmental defects caused by mks3 knockdown. Our results suggest that meckelin forms a functional complex with filamin A that is disrupted in MKS and causes defects in neuronal migration and Wnt signalling. Furthermore, filamin A has a crucial role in the normal processes of ciliogenesis and basal body positioning. Concurrent with these processes, the meckelin-filamin A signalling axis may be a key regulator in maintaining correct, normal levels of Wnt signalling.