The genetic landscape and clinical spectrum of nephronophthisis and related ciliopathies

Nephronophthisis (NPH) is an autosomal-recessive ciliopathy representing one of the most frequent causes of kidney failure in childhood characterized by a broad clinical and genetic heterogeneity. Applied to one of the worldwide largest cohorts of patients with NPH, genetic analysis encompassing targeted and whole exome sequencing identified disease-causing variants in 600 patients from 496 families with a detection rate of 71%. Of 788 pathogenic variants, 40 known ciliopathy genes were identified. However, the majority of patients (53%) bore biallelic pathogenic variants in NPHP1. NPH-causing gene alterations affected all ciliary modules defined by structural and/or functional subdomains. Seventy six percent of these patients had progressed to kidney failure, of which 18% had an infantile form (under five years) and harbored variants affecting the Inversin compartment or intraflagellar transport complex A. Forty eight percent of patients showed a juvenile (5-15 years) and 34% a late-onset disease (over 15 years), the latter mostly carrying variants belonging to the Transition Zone module. Furthermore, while more than 85% of patients with an infantile form presented with extra-kidney manifestations, it only concerned half of juvenile and late onset cases. Eye involvement represented a predominant feature, followed by cerebellar hypoplasia and other brain abnormalities, liver and skeletal defects. The phenotypic variability were in a large part associated with mutation types, genes and corresponding ciliary modules with hypomorphic variants in ciliary genes playing a role in early steps of ciliogenesis associated with juvenile-to-late onset NPH forms. Thus, our data confirm a considerable proportion of late-onset NPH suggesting an underdiagnosis in adult chronic kidney disease.

POS1082 CATASTROPHIZING IN PATIENTS WITH PSORIATIC ARTHRITIS

Background:

Catastrophizing is a negative cognitivo-affective response to an anxiety-provoking stimulus, especially anticipated or actual pain. It can be quickly assessed using a validated questionnaire: the Pain Catastrophizing Scale (PCS)1. Catastrophizing plays a role in maintaining chronic pain and is associated with several pain-related outcomes in osteoarthritis and low back pain. To our knowledge, there are no data on catastrophizing in patients with psoriatic arthritis (PsA).

Objectives:

To assess the prevalence of catastrophizing and associated factors in PsA.

Methods:

We performed a bi-centric observational, prospective study. All patients aged 18 or over with PsA fulfilling the 2006 CASPAR criteria were consecutively included. Sociodemographic data, information on the disease and its treatments were collected as well as questionnaires for disease activity (BASDAI), function (HAQ, BASFI), quality of life (SF12, EQ5D), anxiety and depression (HADS, GAD7), fibromyalgia (FiRST), insomnia (ISI) and catastrophizing scores (PCS). Statistical analysis included samples T-test, one-way variance analysis, Spearman’s correlation coefficient, Chi2 test, Fisher’s exact test, Wilcoxon test, multivariate linear regression (considering catastrophizing as a continuous variable) and multivariate logistics regression (considering catastrophizing as a categorical variable: PCS ≥ 20 = high level catastrophizing).

Results:

From September 2019 to March 2020, 85 PsA patients were included: 54.1% were women, the median age was 54.0 years and 33 patients (39.8%) were professionally active. The majority of patients (88.2%) had a disease lasting for more than 2 years. Axial involvement was found for 39 patients (45.9%), almost all patients (98.8%) had peripheral involvement, 32 patients (37.7%) had enthesitic involvement and 14 patients (16.7%) had erosions. Median DAS28 CRP was 3.12 [2.13-4.46] and the median BASDAI score was 5.50 [4.30-6.70]. The prevalence of a PCS score ≥20 was 45.9% [35.3;56.5]. The median PCS score was 16 [6-29]. In multivariate logistics regression, high-level catastrophizing was significantly associated with the HADS anxiety score (OR=1.35 [1.15-1.61]) and pain VAS (OR=1.04 [1.02-1.06]). In multivariate linear regression, catastrophizing was significantly associated with the HADS anxiety score (p= 0.004), pain VAS (p=0.001), HADS depression score (p=0.018) and insomnia score (p=0.034).

Conclusion:

Almost half the patients with PsA were high catastrophizers. Catastrophizing is related to anxiety, pain, depression and insomnia. It may be interesting to detect catastrophizing in order to improve the care of our patients.

References:

[1]Sullivan MJL. et al. Psychological Assessment. 1995;7(4):524–32

Disclosure of Interests:

None declared.

POS1239 POSITIVE IMPACT OF THE FIRST LOCKDOWN IN PATIENTS WITH CHRONIC INFLAMMATORY RHEUMATISM

Background:

Since the beginning of 2020, the COVID-19 pandemic has caused a considerable amount of fear, worry and concern in the general population and among certain groups such as the elderly, healthcare providers and people with pre-existing conditions in particular. Our patients suffering from chronic inflammatory rheumatism (CIR), a group of autoimmune pathologies treated by immunosuppressant medication, are particularly concerned. Actions taken – particularly quarantine and its effects on the normal activities, habits or livelihoods of many people – also have a significant impact. There is little information on the impact of the lockdown in patients with CIR with data measured prospectively, in a standardized way, before and during the first lockdown period.

Objectives:

The objective of this ancillary study was to evaluate the psychological impact of the first lockdown period (anxiety, depression, sleep disorders, catastrophizing...) as well as the evolution of disease activity in patients suffering from CIR.

Methods:

At two French university hospitals, adult patients with rheumatoid arthritis (RA) according to the ACR-EULAR 2010 criteria, spondyloarthritis (SpA) fulfilling the ASAS 2009 criteria and psoriatic arthritis (PsA) according to the Caspar 2006 criteria were consecutively included in the Catastrophism in Chronic Inflammatory Rheumatism (CRIC) study from September 2019. Sociodemographic data, information on the disease and its treatments were collected as well as questionnaires on disease activity (DAS28, CDAI, BASDAI), function (HAQ), quality of life (SF12, EQ5D), anxiety and depression (HADS, GAD7), insomnia (ISI) and catastrophizing scores (PCS). These data were collected prospectively at baseline, 3, 6 and 12 months.

In this ancillary study, data from patients with an assessment before and during lockdown were analyzed. Statistical analyses were descriptive with a paired Student’s T-test.

Results:

In all, 140 patients (49 RA, 69 SpA and 22 PsA) were evaluated before and during lockdown. The median age was 53.5 [44-63] years and 60.7% were women; 74 patients (53.2%) were professionally active and 102 (72.9%) were living as couples. The majority of patients (92.9 %) had a disease lasting more than 2 years. Concerning treatments, 63 (45%) were treated by bDMARD monotherapy, 40 (28.5%) by bDMARD+ csDMARD, 17 (12.1%) by csDMARD monotherapy and 2 patients by tsDMARD; 90.7% were not taking any corticosteroids and 8.6% were taking ≤5 mg/d; 30% were on NSAIDs.

When comparing before and during lockdown, pain, tender joint count, swollen joint count, disease activity (CDAI, BASDAI) and function (HAQ, SF12 physical component) were similar. However, there was a significant improvement in psychological status, anxiety (HADS, GAD7), the mental component of SF12, catastrophizing and overall quality of life (EQ5D) (see Table 1 below).

Conclusion:

There are very few prospective, standardized data on the impact of lockdown in patients with CIR with an assessment before and during the first lockdown period. In patients with CIR, the first lockdown period had no impact on the activity of the disease and was well experienced psychologically with less anxiety and an improvement in quality of life.

Table 1.Outcome (N)140 CIR: 49 RA, 69 SpA, 22 PsABefore lockdownMean (SD)During lockdownMean (SD)Mean change(SD)PPain VAS (138)39.4 (25.3)39.4 (25.0)-0.28 (27.1)NSTJC (57)4.0 (6.8)4.7 (4.4)0.7 (5.9)NSSJC (56)1.0 (2.6)1.6 (1.7)0.5 (2.4)NSCDAI (36)11.7 (1.4)12.3 (7.5)1.2 (8.7)NSBASDAI (84)4.7 (1.9)4.9 (2.0)0.14 (1.4)NSHAQ (135)0.72 (0.57)0.72 (0.53)0.03 (0.33)NSSF12 mental(136)32.7 (8.7)36.2 (8.4)3.46 (8.01)<0.0001GAD-7 (anxiety) (135)7.7 (5.5)5.0 (5.3)-1.73 (0.40)<0.0001HADS anxiety(137)8.5 (3.9)7.8 (3.9)-0.64 (2.91)0.0113EQ5D(139)0.55 (0.31)0.61 (0.29)0.06 (0.24)0.0078PCS (catastrophizing) (137)18.9 (13.3)15.9 (11.1)-3.10 (9.60)0.0003

Disclosure of Interests:

None declared

POS1003 CATASTROPHIZING IN PATIENTS WITH SPONDYLOARTHRITIS

Background:

Catastrophizing is a negative cognitivo-affective response to an anxiety-provoking stimulus, especially anticipated or actual pain. It can be assessed quickly using a validated questionnaire: the Pain Catastrophizing Scale (PCS)1. Catastrophizing plays a role in maintaining chronic pain and is associated with several pain-related outcomes in osteoarthritis and low back pain. There is a lack of knowledge about catastrophizing in axial spondyloarthritis (AS) with only one study2 so far.

Objectives:

To assess the prevalence of catastrophizing and associated factors in spondyloarthritis.

Methods:

We performed an observational, prospective, bi-centric study. All patients aged 18 or over with AS fulfilling the 2009 Assessment in Spondyloarthritis International Society (ASAS) criteria were consecutively included. Sociodemographic data, information on the disease and its treatments were collected as well as questionnaires regarding disease activity (BASDAI), function (HAQ, BASFI), quality of life (SF12, EQ5D), anxiety and depression (HADS, GAD7), fibromyalgia (FiRST), insomnia (ISI) and catastrophizing scores (PCS). Statistical analysis included a samples t-test, one-way variance analysis, Spearman’s correlation coefficient, the Chi2 test, Fisher’s exact test, the Wilcoxon test, multivariate linear regression (considering catastrophizing as a continuous variable) and multivariate logistics regression (considering catastrophizing as a categorical variable: PCS ≥ 20 = high level catastrophizing).

Results:

From September 2019 to March 2020, 168 AS patients were included: 48.5% were women, the median age was 48.5 years and 100 patients (60.2%) were professionally active. Almost all patients (95.8%) had a disease lasting for more than 2 years; 110 (72%) were HLA-B27+; 84 (50%) had MRI sacroiliitis and 62 (37.6%) radiographic sacroiliitis. In all, 166 (98.8%) had axial involvement, 99 (58.9%) had peripheral involvement and 44 (26.2%) had enthesitic involvement. The median BASDAI score was 6.30 [Q1-Q3 4.65-6.30].

The prevalence of a PCS score ≥20 was 45.5% [38.0;53.0]. The median PCS score was 18 [7-27]. In multivariate logistics regression, high-level catastrophizing was significantly associated with the HADS anxiety score (OR=1.54 [1.22-2.0]), HADS depression score (OR=1.25 [1.10-1.43]) and disease activity (BASDAI OR=1.14 [1.01-1.26]). In multivariate linear regression, catastrophizing was also significantly associated with anxiety (p<0.0001), depression (p<0.0001) and disease activity (p=0.0008).

Conclusion:

Almost half the patients with AS were high catastrophizers. Catastrophizing is linked to anxiety, depression, and disease activity. It may be interesting to detect catastrophizing in order to improve the management of our patients.

References:

[1]Sullivan MJL. et al. Psychological Assessment. 1995;7(4):524–32

[2]Penhoat M. et al. Joint Bone Spine. 2014;81(3):235–9

Disclosure of Interests:

None declared.

POS0566 CATASTROPHIZING IN PATIENTS WITH RHEUMATOID ARTHRITIS

Background:

Catastrophizing is conceptualized as a negative cognitive–affective response to an anxiety-provoking stimulus, especially anticipated or actual pain. Catastrophizing can be assessed quickly using a validated questionnaire: the Pain Catastrophizing Scale (PCS)1. Catastrophizing plays a role in maintaining chronic pain and is associated with several pain-related outcomes in osteoarthritis and low back pain.

Objectives:

To assess the prevalence of catastrophizing and associated factors in rheumatoid arthritis (RA).

Methods:

We performed an observational, prospective, bi-centric study. All patients aged 18 or over with RA and fulfilling the ACR-EULAR 2010 criteria were consecutively included. Sociodemographic data, information on the disease and its treatments were collected as well as questionnaires for disease activity (DAS28), function (HAQ), quality of life (SF12, EQ5D), anxiety and depression (HADS, GAD7), fibromyalgia (FiRST), insomnia (ISI) and catastrophizing scores (PCS). Statistical analysis included the samples t-test, one-way variance analysis, the Spearman’s correlation test, the Chi2 test, Fisher’s exact test, the Wilcoxon test, multivariate linear regression (considering catastrophizing as a continuous variable) and multivariate logistics regression (considering catastrophizing as a categorical variable: PCS ≥ 20 = high level catastrophizing).

Results:

From September 2019 to March 2020, 201 patients with RA were included: 78.1% were women and the median age was 63.0 years. In all, 64.1% of patients were RF+, 65.7% ACPA+, and 46% had erosive disease. Median DAS28 CRP was 2.9 [2.1-4.0]. with 45% of patients in remission, 14.8% with low, 31.2% moderate and 9 % high activity. The majority of patients (92 %) had a disease lasting for more than 2 years.

The prevalence of a PCS score ≥20 was 48.0% [41.0;54.9]. The median PCS score was 18 [7-28]. In multivariate logistics regression, high-level catastrophizing was significantly associated with DAS28-CRP (OR= 1.61 [1.18-2.20]), HADS anxiety score (OR=1.25 [1.11-1.40]) and the HADS depression score (OR=1.19 [1.07-1.33]). In multivariate linear regression, catastrophizing was significantly associated with the HADS anxiety score (p< 0.0001), HADS depression score (p=0.0055), HAQ (p=0.0015) and the ISI insomnia score (p=0.005).

Conclusion:

Almost half the patients with RA were high catastrophizers. Catastrophizing is linked to anxiety, depression, disease activity, function impairment and insomnia. It may be interesting to detect catastrophizing in order to improve the management of our patients.

References:

[1]Sullivan MJL. et al. Psychological Assessment. 1995;7(4):524–32

Disclosure of Interests:

None declared

FRI0101 EFFECTS OF IL6 INHIBITORS ON THE INCIDENCE OF MAJOR ADVERSE CARDIOVASCULAR EVENTS IN RHEUMATOID ARTHRITIS PATIENTS: A SYSTEMATIC REVIEW WITH META ANALYSIS

Background:

Rheumatoid arthritis (RA) is associated with a 2 fold increased risk of cardiovascular events (CVE) and mortality when compared to the general population. The systemic inflammation in RA seems to play a pivotal role by creating endothelial dysfunction and thus accelerating atherosclerosis. This long lasting inflammatory process potentiates the effects of additional classical cardiovascular risk factors. Since the 2000s, numerous therapeutic advances, in particular biologics, allow better control of this inflammation. Among these, IL6 inhibitors (IL6i) are known to provide rapid and sustained improvements in clinical, biological and radiographic outcomes. However, an increase in circulating lipid concentrations in patients treated with IL6i is usual. This raises the question of the risk -to -benefit ratio of IL6i.

Objectives:

The purpose of this systematic literature review and meta-analysis was to evaluate the impact of IL6i on the incidence of major adverse cardiovascular events in RA patients in comparison with TNFalpha inhibitors (TNFi), non TNFi bDMARDs or csDMARDS.

Methods:

A systematic literature search of MEDLINE (via PubMed), EMBASE and the Cochrane Library databases until February 2019 was performed. Included studies were observational studies or randomized controlled trials having reported relevant confirmed CVEs (death from CVE, myocardial infarction, heart failure and stroke) in patients with RA treated with IL6i, and a suitable control group. A meta-analysis of the relative risk for each CVE in RA patients treated with IL6i compared to patients in the control groups was performed. A random effect model was applied in case of substantial heterogeneity.

Results:

Of 6869 studies, 23 randomized controlled trials and 6 controlled cohorts could be included. IL6i were significantly associated with a reduction in the risk of myocardial infarction in comparison with TNFi (OR, 0.73; 95% CI [0.56 to 0.96]). No other significant effects were observed with regard to the risks of stroke, heart failure (HF), and death from CVE in comparison with csDMARDs, TNFi, or non-TNFi bDMARDs (table 1).

Table 1.

Pooled relative risks of cardiovascular events in RA patients treated with IL-6 inhibitors and respective control groups

Cs DMARDSTNFiNon TNFi bDMARDSMyocardial infarction1.44 [0.50;4.17]0.73 [0.56; 0.96]0.81 [0.48; 1.36]Stroke1.08 [0.40; 2.91]1.20 [0.82; 1.77]0.73 [0.39; 1.37]Heart failure0.17 [0.01; 4.08]1.51 [0.61; 3.70]1.19 [0.71; 1.98]Cardiovascular death1.59 [0.62; 4.11]1.13 [0.72; 1.78]NA

Our findings of a potentially protective effect of IL6i use on the risk of MI are reassuring. Although several beneficial effects might be involved, like the effective control of systemic inflammation, the anti-arrhythmia effect or the improvement of endothelial and left ventricle dysfunction, a potential indication bias with a decreased likelihood to prescribe these drugs in patients with high cardiovascular risk cannot be excluded.

Conclusion:

This review of the literature with meta-analysis provides reassuring results about the association between use of IL6i and CVE in RA patients. Data from long-term observational studies is however needful to confirm and ascertain this result.

Disclosure of Interests:

None declared

Genetic heterogeneity of polydactyly in Maine Coon cats

OBJECTIVES

Polydactyly has been described in two breeds of domestic cats (Maine Coon and Pixie Bob) and in some outbred domestic cats (eg, Hemingway cats). In most cases, feline polydactyly is a non-syndromic preaxial polydactyly. Three variants located in a regulatory sequence involved in limb development, named ZRS (zone of polarising activity regulatory sequence), have been identified to be responsible for feline polydactyly. These variants have been found in outbred domestic cats in the UK (UK1 and UK2 variants) and in Hemingway cats in the USA (Hw variant). The aim of this study was to characterise the genetic features of polydactyly in Maine Coon cats.

METHODS

Genotyping assay was used to identify the variant(s) segregating in a cohort of 75 polydactyl and non-polydactyl Maine Coon cats from different breeding lines from Europe, Canada and the USA. The authors performed a segregation analysis to identify the inheritance pattern of polydactyly in this cohort and analysed the population structure.

RESULTS

The Hw allele was identified in a subset of polydactyl cats. Sequencing of two regulatory sequences involved in limb development did not reveal any other variant in polydactyl cats lacking the Hw allele. Additionally, genotype-phenotype and segregation analyses revealed the peculiar inheritance pattern of polydactyly in Maine Coon cats. The population structure analysis demonstrated a genetic distinction between Hw and Hw-free polydactyl cats.

CONCLUSIONS AND RELEVANCE

Polydactyly in Maine Coon cats is inherited as an autosomal dominant trait with incomplete penetrance and variable expressivity, and this trait is characterised by genetic heterogeneity in the Maine Coon breed. Maine Coon breeders should be aware of this situation and adapt their breeding practices accordingly.

Functional characterization of tektin-1 in motile cilia and evidence for TEKT1 as a new candidate gene for motile ciliopathies

A child presenting with Mainzer-Saldino syndrome (MZSDS), characterized by renal, retinal and skeletal involvements, was also diagnosed with lung infections and airway ciliary dyskinesia. These manifestations suggested dysfunction of both primary and motile cilia, respectively. Targeted exome sequencing identified biallelic mutations in WDR19, encoding an IFT-A subunit previously associated with MZSDS-related chondrodysplasia, Jeune asphyxiating thoracic dysplasia and cranioectodermal dysplasia, linked to primary cilia dysfunction, and in TEKT1 which encodes tektin-1 an uncharacterized member of the tektin family, mutations of which may cause ciliary dyskinesia. Tektin-1 localizes at the centrosome in cycling cells, at basal bodies of both primary and motile cilia and to the axoneme of motile cilia in airway cells. The identified mutations impaired these localizations. In addition, airway cells from the affected individual showed severe motility defects without major ultrastructural changes. Knockdown of tekt1 in zebrafish resulted in phenotypes consistent with a function for tektin-1 in ciliary motility, which was confirmed by live imaging. Finally, experiments in the zebrafish also revealed a synergistic effect of tekt1 and wdr19. Altogether, our data show genetic interactions between WDR19 and TEKT1 likely contributing to the overall clinical phenotype observed in the affected individual and provide strong evidence for TEKT1 as a new candidate gene for primary ciliary dyskinesia.

Mutations in MAPKBP1 Cause Juvenile or Late-Onset Cilia-Independent Nephronophthisis

Nephronophthisis (NPH), an autosomal-recessive tubulointerstitial nephritis, is the most common cause of hereditary end-stage renal disease in the first three decades of life. Since most NPH gene products (NPHP) function at the primary cilium, NPH is classified as a ciliopathy. We identified mutations in a candidate gene in eight individuals from five families presenting late-onset NPH with massive renal fibrosis. This gene encodes MAPKBP1, a poorly characterized scaffolding protein for JNK signaling. Immunofluorescence analyses showed that MAPKBP1 is not present at the primary cilium and that fibroblasts from affected individuals did not display ciliogenesis defects, indicating that MAPKBP1 may represent a new family of NPHP not involved in cilia-associated functions. Instead, MAPKBP1 is recruited to mitotic spindle poles (MSPs) during the early phases of mitosis where it colocalizes with its paralog WDR62, which plays a key role at MSP. Detected mutations compromise recruitment of MAPKBP1 to the MSP and/or its interaction with JNK2 or WDR62. Additionally, we show increased DNA damage response signaling in fibroblasts from affected individuals and upon knockdown of Mapkbp1 in murine cell lines, a phenotype previously associated with NPH. In conclusion, we identified mutations in MAPKBP1 as a genetic cause of juvenile or late-onset and cilia-independent NPH.

Novel NEK8 Mutations Cause Severe Syndromic Renal Cystic Dysplasia through YAP Dysregulation

Ciliopathies are a group of genetic multi-systemic disorders related to dysfunction of the primary cilium, a sensory organelle present at the cell surface that regulates key signaling pathways during development and tissue homeostasis. In order to identify novel genes whose mutations would cause severe developmental ciliopathies, >500 patients/fetuses were analyzed by a targeted high throughput sequencing approach allowing exome sequencing of >1200 ciliary genes. NEK8/NPHP9 mutations were identified in five cases with severe overlapping phenotypes including renal cystic dysplasia/hypodysplasia, situs inversus, cardiopathy with hypertrophic septum and bile duct paucity. These cases highlight a genotype-phenotype correlation, with missense and nonsense mutations associated with hypodysplasia and enlarged cystic organs, respectively. Functional analyses of NEK8 mutations in patient fibroblasts and mIMCD3 cells showed that these mutations differentially affect ciliogenesis, proliferation/apoptosis/DNA damage response, as well as epithelial morphogenesis. Notably, missense mutations exacerbated some of the defects due to NEK8 loss of function, highlighting their likely gain-of-function effect. We also showed that NEK8 missense and loss-of-function mutations differentially affect the regulation of the main Hippo signaling effector, YAP, as well as the expression of its target genes in patient fibroblasts and renal cells. YAP imbalance was also observed in enlarged spheroids of Nek8-invalidated renal epithelial cells grown in 3D culture, as well as in cystic kidneys of Jck mice. Moreover, co-injection of nek8 MO with WT or mutated NEK8-GFP RNA in zebrafish embryos led to shortened dorsally curved body axis, similar to embryos injected with human YAP RNA. Finally, treatment with Verteporfin, an inhibitor of YAP transcriptional activity, partially rescued the 3D spheroid defects of Nek8-invalidated cells and the abnormalities of NEK8-overexpressing zebrafish embryos. Altogether, our study demonstrates that NEK8 human mutations cause major organ developmental defects due to altered ciliogenesis and cell differentiation/proliferation through deregulation of the Hippo pathway.

Genes mutated in ciliopathies encode proteins with various localizations and functions at the primary cilium. Here we report novel NEK8 mutations in patients with renal cystic hypodysplasia and associated ciliopathy defects. NEK8 belongs to a protein complex defining the Inversin compartment of the cilium. It is also a negative regulator of the Hippo signaling pathway that controls organ growth. We report genotype-phenotype correlation in the patients. We functionally demonstrate that the two types of mutations (missense versus nonsense) differentially affect ciliogenesis, cell apoptosis and epithelialisation. We also show that all the mutations lead to dysregulation of the Hippo pathway through nuclear YAP imbalance but that the nature of this imbalance is different according to the type of mutation. We confirm alteration of the Hippo pathway associated with Nek8 mutation in vivo in Jck mice. Remarkably, we show that morphogenesis defects observed in Nek8 knockdown epithelial cells or zebrafish embryos are rescued by Verteporfin, a specific inhibitor of YAP transcriptional activity, demonstrating the causative role of YAP dysregulation in the occurrence of these defects. Altogether, this study links NEK8 mutations to dysregulation of the Hippo pathway and provide molecular clues to understand the variability of the multiorgan defects in the patients.

Mutations in TRAF3IP1/IFT54 reveal a new role for IFT proteins in microtubule stabilization

Ciliopathies are a large group of clinically and genetically heterogeneous disorders caused by defects in primary cilia. Here we identified mutations in TRAF3IP1 (TNF Receptor-Associated Factor Interacting Protein 1) in eight patients from five families with nephronophthisis (NPH) and retinal degeneration, two of the most common manifestations of ciliopathies. TRAF3IP1 encodes IFT54, a subunit of the IFT-B complex required for ciliogenesis. The identified mutations result in mild ciliary defects in patients but also reveal an unexpected role of IFT54 as a negative regulator of microtubule stability via MAP4 (microtubule-associated protein 4). Microtubule defects are associated with altered epithelialization/polarity in renal cells and with pronephric cysts and microphthalmia in zebrafish embryos. Our findings highlight the regulation of cytoplasmic microtubule dynamics as a role of the IFT54 protein beyond the cilium, contributing to the development of NPH-related ciliopathies.

Nephrophthisis (NPH) is a common manifestation of ciliopathy diseases. Here the authors identify mutations in intraflagellar transport 54 (IFT54) in patients with NPH and discover an extra-ciliary role for IFT54 in regulating cytoplasmic microtubule dynamics, that contributes to the pathophysiology of this disease.

A homozygous PDE6D mutation in Joubert syndrome impairs targeting of farnesylated INPP5E protein to the primary cilium

Joubert syndrome (JS) is characterized by a distinctive cerebellar structural defect, namely the << molar tooth sign >>. JS is genetically heterogeneous, involving 20 genes identified to date, which are all required for cilia biogenesis and/or function. In a consanguineous family with JS associated with optic nerve coloboma, kidney hypoplasia, and polydactyly, combined exome sequencing and mapping identified a homozygous splice-site mutation in PDE6D, encoding a prenyl-binding protein. We found that pde6d depletion in zebrafish leads to renal and retinal developmental anomalies and wild-type but not mutant PDE6D is able to rescue this phenotype. Proteomic analysis identified INPP5E, whose mutations also lead to JS or mental retardation, obesity, congenital retinal dystrophy, and micropenis syndromes, as novel prenyl-dependent cargo of PDE6D. Mutant PDE6D shows reduced binding to INPP5E, which fails to localize to primary cilia in patient fibroblasts and tissues. Furthermore, mutant PDE6D is unable to bind to GTP-bound ARL3, which acts as a cargo-release factor for PDE6D-bound INPP5E. Altogether, these results indicate that PDE6D is required for INPP5E ciliary targeting and suggest a broader role for PDE6D in targeting other prenylated proteins to the cilia. This study identifies PDE6D as a novel JS disease gene and provides the first evidence of prenyl-binding-dependent trafficking in ciliopathies.

Mutations of CEP83 cause infantile nephronophthisis and intellectual disability

Ciliopathies are a group of hereditary disorders associated with defects in cilia structure and function. The distal appendages (DAPs) of centrioles are involved in the docking and anchoring of the mother centriole to the cellular membrane during ciliogenesis. The molecular composition of DAPs was recently elucidated and mutations in two genes encoding DAPs components (CEP164/NPHP15, SCLT1) have been associated with human ciliopathies, namely nephronophthisis and orofaciodigital syndrome. To identify additional DAP components defective in ciliopathies, we independently performed targeted exon sequencing of 1,221 genes associated with cilia and 5 known DAP protein-encoding genes in 1,255 individuals with a nephronophthisis-related ciliopathy. We thereby detected biallelic mutations in a key component of DAP-encoding gene, CEP83, in seven families. All affected individuals had early-onset nephronophthisis and four out of eight displayed learning disability and/or hydrocephalus. Fibroblasts and tubular renal cells from affected individuals showed an altered DAP composition and ciliary defects. In summary, we have identified mutations in CEP83, another DAP-component-encoding gene, as a cause of infantile nephronophthisis associated with central nervous system abnormalities in half of the individuals.

A homozygous missense mutation in the ciliary gene TTC21B causes familial FSGS

Several genes, mainly involved in podocyte cytoskeleton regulation, have been implicated in familial forms of primary FSGS. We identified a homozygous missense mutation (p.P209L) in the TTC21B gene in seven families with FSGS. Mutations in this ciliary gene were previously reported to cause nephronophthisis, a chronic tubulointerstitial nephropathy. Notably, tubular basement membrane thickening reminiscent of that observed in nephronophthisis was present in patients with FSGS and the p.P209L mutation. We demonstrated that the TTC21B gene product IFT139, an intraflagellar transport-A component, mainly localizes at the base of the primary cilium in developing podocytes from human fetal tissue and in undifferentiated cultured podocytes. In contrast, in nonciliated adult podocytes and differentiated cultured cells, IFT139 relocalized along the extended microtubule network. We further showed that knockdown of IFT139 in podocytes leads to primary cilia defects, abnormal cell migration, and cytoskeleton alterations, which can be partially rescued by p.P209L overexpression, indicating its hypomorphic effect. Our results demonstrate the involvement of a ciliary gene in a glomerular disorder and point to a critical function of IFT139 in podocytes. Altogether, these data suggest that this homozygous TTC21B p.P209L mutation leads to a novel hereditary kidney disorder with both glomerular and tubulointerstitial damages.

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.

ANKS6 is a central component of a nephronophthisis module linking NEK8 to INVS and NPHP3

Nephronophthisis (NPH) is an autosomal recessive cystic kidney disease that leads to renal failure in childhood or adolescence. Most NPHP gene products form molecular networks. We have identified ANKS6 as a new NPHP family member that connects NEK8 (NPHP9) to INVERSIN (INVS, NPHP2) and NPHP3 to form a distinct NPHP module. ANKS6 localizes to the proximal cilium and knockdown experiments in zebrafish and Xenopus confirmed a role in renal development. Genetic screening identified six families with ANKS6 mutations and NPH, including severe cardiovascular abnormalities, liver fibrosis and situs inversus. The oxygen sensor HIF1AN (FIH) hydroxylates ANKS6 and INVS, while knockdown of Hif1an in Xenopus resembled the loss of other NPHP proteins. HIF1AN altered the composition of the ANKS6/INVS/NPHP3 module. Network analyses, uncovering additional putative NPHP-associated genes, placed ANKS6 at the center of the NPHP module, explaining the overlapping disease manifestation caused by mutations of either ANKS6, NEK8, INVS or NPHP3.

Mainzer-Saldino syndrome is a ciliopathy caused by IFT140 mutations

Mainzer-Saldino syndrome (MSS) is a rare disorder characterized by phalangeal cone-shaped epiphyses, chronic renal failure, and early-onset, severe retinal dystrophy. Through a combination of ciliome resequencing and Sanger sequencing, we identified IFT140 mutations in six MSS families and in a family with the clinically overlapping Jeune syndrome. IFT140 is one of the six currently known components of the intraflagellar transport complex A (IFT-A) that regulates retrograde protein transport in ciliated cells. Ciliary abundance and localization of anterograde IFTs were altered in fibroblasts of affected individuals, a result that supports the pivotal role of IFT140 in proper development and function of ciliated cells.

Ciliopathies with skeletal anomalies and renal insufficiency due to mutations in the IFT-A gene WDR19

A subset of ciliopathies, including Sensenbrenner, Jeune, and short-rib polydactyly syndromes are characterized by skeletal anomalies accompanied by multiorgan defects such as chronic renal failure and retinitis pigmentosa. Through exome sequencing we identified compound heterozygous mutations in WDR19 in a Norwegian family with Sensenbrenner syndrome. In a Dutch family with the clinically overlapping Jeune syndrome, a homozygous missense mutation in the same gene was found. Both families displayed a nephronophthisis-like nephropathy. Independently, we also identified compound heterozygous WDR19 mutations by exome sequencing in a Moroccan family with isolated nephronophthisis. WDR19 encodes IFT144, a member of the intraflagellar transport (IFT) complex A that drives retrograde ciliary transport. We show that IFT144 is absent from the cilia of fibroblasts from one of the Sensenbrenner patients and that ciliary abundance and morphology is perturbed, demonstrating the ciliary pathogenesis. Our results suggest that isolated nephronophthisis, Jeune, and Sensenbrenner syndromes are clinically overlapping disorders that can result from a similar molecular cause.