Skewed X-chromosome inactivation drives the proportion of DNAAF6-defective airway motile cilia and variable expressivity in primary ciliary dyskinesia.

BACKGROUND: Primary ciliary dyskinesia (PCD) is a rare airway disorder caused by defective motile cilia. Only male patients have been reported with pathogenic mutations in X-linked DNAAF6, which result in the absence of ciliary dynein arms, whereas their heterozygous mothers are supposedly healthy. Our objective was to assess the possible clinical and ciliary consequences of X-chromosome inactivation (XCI) in these mothers. METHODS: XCI patterns of six mothers of male patients with DNAAF6-related PCD were determined by DNA-methylation studies and compared with their clinical phenotype (6/6 mothers), as well as their ciliary phenotype (4/6 mothers), as assessed by immunofluorescence and high-speed videomicroscopy analyses. The mutated X chromosome was tracked to assess the percentage of cells with a normal inactivated DNAAF6 allele. RESULTS: The mothers' phenotypes ranged from absence of symptoms to mild/moderate or severe airway phenotypes, closely reflecting their XCI pattern. Analyses of the symptomatic mothers' airway ciliated cells revealed the coexistence of normal cells and cells with immotile cilia lacking dynein arms, whose ratio closely mirrored their XCI pattern. CONCLUSION: This study highlights the importance of searching for heterozygous pathogenic DNAAF6 mutations in all female relatives of male PCD patients with a DNAAF6 defect, as well as in females consulting for mild chronic respiratory symptoms. Our results also demonstrate that about one-third-ranging from 20% to 50%-normal ciliated airway cells sufficed to avoid severe PCD, a result paving the way for gene therapy.

A critical region of A20 unveiled by missense TNFAIP3 variations that lead to autoinflammation.

A20 haploinsufficiency (HA20) is an autoinflammatory disease caused by heterozygous loss-of-function variations in TNFAIP3, the gene encoding the A20 protein. Diagnosis of HA20 is challenging due to its heterogeneous clinical presentation and the lack of pathognomonic symptoms. While the pathogenic effect of TNFAIP3 truncating variations is clearly established, that of missense variations is difficult to determine. Herein, we identified a novel TNFAIP3 variation, p.(Leu236Pro), located in the A20 ovarian tumor (OTU) domain and demonstrated its pathogenicity. In the patients' primary cells, we observed reduced A20 levels. Protein destabilization was predicted in silico for A20_Leu236Pro and enhanced proteasomal degradation was confirmed in vitro through a flow cytometry-based functional assay. By applying this approach to the study of another missense variant, A20_Leu275Pro, for which no functional characterization has been performed to date, we showed that this variant also undergoes enhanced proteasomal degradation. Moreover, we showed a disrupted ability of A20_Leu236Pro to inhibit the NF-κB pathway and to deubiquitinate its substrate TRAF6. Structural modeling revealed that two residues involved in OTU pathogenic missense variations (i.e. Glu192Lys and Cys243Tyr) establish common interactions with Leu236. Interpretation of newly identified missense variations is challenging, requiring, as illustrated here, functional demonstration of their pathogenicity. Together with functional studies, in silico structure analysis is a valuable approach that allowed us (i) to provide a mechanistic explanation for the haploinsufficiency resulting from missense variations and (ii) to unveil a region within the OTU domain critical for A20 function.

Germline RUNX1 variants in paediatric patients in a French specialised centre.

Familial platelet disorder with associated myeloid malignancy (FPD-MM; OMIM 601399) is related to germline RUNX1 mutation. The pathogenicity of RUNX1 variants was initially linked to FPD-MM phenotype, but the discovery of new variants through the expansion of genetic explorations in leukaemia is questioning this assertion. In this study, we add 10 families with germline RUNX1 variant explored at Armand Trousseau Hospital for leukaemia diagnosis or thrombocytopenia, to the 259 described so far. Detailed description of their personal and family history of haematological pathologies allows identifying three phenotypes related to germline RUNX1 variants: thrombocytopenia and/or malignant haematological disease with family history of haematological diseases, thrombocytopenia with no family history of haematological diseases and acute lymphoblastic leukaemia (ALL) with no family history of haematological diseases. In the latter phenotype, ALL characteristics involving RUNX1 suggest the implication of germline variants in the onset of the malignancy.

De Novo Gain-Of-Function Variations in LYN Associated With an Early-Onset Systemic Autoinflammatory Disorder.

OBJECTIVE: To identify the molecular basis of a severe systemic autoinflammatory disorder (SAID) and define its main phenotypic features, and to functionally assess the sequence variations identified in LYN, a gene encoding a nonreceptor tyrosine kinase. METHODS: We used targeted next-generation sequencing and in vitro functional studies of Lyn phosphorylation state and Lyn-dependent NF-κB activity after expression of recombinant Lyn isoforms carrying different sequence variations. RESULTS: We identified a de novo LYN variation (p.Tyr508His) in a patient presenting since birth with recurrent fever, chronic urticaria, atopic dermatitis, arthralgia, increased inflammatory biomarkers, and elevated plasma cytokine levels. We studied the consequences on Lyn phosphorylation state of the p.Tyr508His variation and of the 2 LYN variations reported so far (p.Tyr508Phe and p.Tyr508*), and found that all 3 variations prevent phosphorylation of residue 508 and lead to autophosphorylation of Tyr397. Additionally, these 3 LYN variations activate the NF-κB pathway. These results show a gain-of-function effect of the variations involving Tyr508 on Lyn activity. CONCLUSION: This study demonstrates the pathogenicity of the first 3 LYN variations identified in SAID patients and delineates the phenotypic spectrum of a disease entity characterized by severe, early-onset, systemic inflammatory disease affecting neonates with no family history of SAID. All 3 LYN variations affect the same tyrosine residue located in the C-terminus of Lyn, thereby demonstrating the critical role of this residue in the proper regulation of Lyn activity in humans.

RNF213-associated urticarial lesions with hypercytokinemia.

BACKGROUND: Urticarial lesions are observed in both cutaneous and systemic disorders. Familial forms of urticarial syndromes are rare and can be encountered in systemic autoinflammatory diseases. OBJECTIVE: We sought to investigate a large family with dominantly inherited chronic urticarial lesions associated with hypercytokinemia. METHODS: We performed a genetic linkage analysis in 14 patients from a 5-generation family, as well as whole-exome sequencing, cytokine profiling, and transcriptomic analyses on samples from 2 patients. The identified candidate protein was studied after in vitro expression of the corresponding normal and mutated recombinant proteins. An unsupervised proteomic approach was used to unveil the associated protein network. RESULTS: The disease phenotype of the most affected family members is characterized by chronic urticarial flares associated with extremely high plasma levels of proinflammatory (IL-1ß, IL-6, and TNF-α) and anti-inflammatory (IL-10 and IL-1 receptor antagonist [IL-1RA]) cytokines, with no secondary organ dysfunction, no susceptibility to infections, no fever, and normal C-reactive protein levels. Monocyte transcriptomic analyses identified an immunotolerant profile in the most affected patient. The affected family members carried a loss-of-function mutation in RNF213 that encodes mysterin, a protein with a poorly known physiologic role. We identified the deubiquitinase CYLD, a major regulator of inflammation, as an RNF213 partner and showed that CYLD expression is inhibited by wild-type but not mutant RNF213. CONCLUSION: We identified a new entity characterized by chronic urticarial lesions associated with a clinically blunted hypercytokinemia. This disease, which is due to loss of function of RNF213, reveals mysterin's key role in the complex molecular network of innate immunity.

Mosaic variants in TNFRSF1A: an emerging cause of tumour necrosis factor receptor-associated periodic syndrome.

OBJECTIVE: To identify the molecular basis of a systemic autoinflammatory disorder (SAID) evocative of TNF receptor-associated periodic syndrome (TRAPS). METHODS: (i) Deep next generation sequencing (NGS) through a SAID gene panel; (ii) variant allele distribution in peripheral blood subpopulations; (iii) in silico analyses of mosaic variants using TNF receptor superfamily 1A (TNFRSF1A) crystal structure; (iv) review of the very rare TNFRSF1A mosaic variants reported previously. RESULTS: In a 36-year-old man suffering from recurrent fever for 12 years, high-depth NGS revealed a TNFRSF1A mosaic variant, c.176G>A p.(Cys59Tyr), which Sanger sequencing failed to detect. This mosaic variant displayed a variant allele fraction of 14% in whole blood; it affects both myeloid and lymphoid lineages. p.(Cys59Tyr), a recurrent germline pathogenic variant, affects a crucial cysteine located in the first cysteine-rich domain (CRD1) and involved in a disulphide bridge. Introduction of a tyrosine at this position is expected to disrupt the CRD1 structure. Review of the three previously reported TNFRSF1A mosaic variants revealed that they are all located in a small region of CRD2 and that germinal cells can be affected. CONCLUSION: This study expands the localization of TNFRSF1A mosaic variants to the CRD1 domain. Noticeably, residues involved in germline TNFRSF1A mutational hot spots can also be involved in post-zygotic mutational events. Including our study, only four patients have been thus far reported with TNFRSF1A mosaicism, highlighting the need for a high-depth NGS-based approach to avoid the misdiagnosis of TRAPS. Genetic counselling has to consider the potential occurrence of TNFRSF1A mosaic variants in germinal cells.

Functional assessment and phenotypic heterogeneity of SFTPA1 and SFTPA2 mutations in interstitial lung diseases and lung cancer.

INTRODUCTION: Interstitial lung diseases (ILDs) can be caused by mutations in the SFTPA1 and SFTPA2 genes, which encode the surfactant protein (SP) complex SP-A. Only 11 SFTPA1 or SFTPA2 mutations have so far been reported worldwide, of which five have been functionally assessed. In the framework of ILD molecular diagnosis, we identified 14 independent patients with pathogenic SFTPA1 or SFTPA2 mutations. The present study aimed to functionally assess the 11 different mutations identified and to accurately describe the disease phenotype of the patients and their affected relatives. METHODS: The consequences of the 11 SFTPA1 or SFTPA2 mutations were analysed both in vitro, by studying the production and secretion of the corresponding mutated proteins and ex vivo, by analysing SP-A expression in lung tissue samples. The associated disease phenotypes were documented. RESULTS: For the 11 identified mutations, protein production was preserved but secretion was abolished. The expression pattern of lung SP-A available in six patients was altered and the family history reported ILD and/or lung adenocarcinoma in 13 out of 14 families (93%). Among the 28 SFTPA1 or SFTPA2 mutation carriers, the mean age at ILD onset was 45 years (range 0.6-65 years) and 48% underwent lung transplantation (mean age 51 years). Seven carriers were asymptomatic. DISCUSSION: This study, which expands the molecular and clinical spectrum of SP-A disorders, shows that pathogenic SFTPA1 or SFTPA2 mutations share similar consequences for SP-A secretion in cell models and in lung tissue immunostaining, whereas they are associated with a highly variable phenotypic expression of disease, ranging from severe forms requiring lung transplantation to incomplete penetrance.

TTC12 Loss-of-Function Mutations Cause Primary Ciliary Dyskinesia and Unveil Distinct Dynein Assembly Mechanisms in Motile Cilia Versus Flagella.

Cilia and flagella are evolutionarily conserved organelles whose motility relies on the outer and inner dynein arm complexes (ODAs and IDAs). Defects in ODAs and IDAs result in primary ciliary dyskinesia (PCD), a disease characterized by recurrent airway infections and male infertility. PCD mutations in assembly factors have been shown to cause a combined ODA-IDA defect, affecting both cilia and flagella. We identified four loss-of-function mutations in TTC12, which encodes a cytoplasmic protein, in four independent families in which affected individuals displayed a peculiar PCD phenotype characterized by the absence of ODAs and IDAs in sperm flagella, contrasting with the absence of only IDAs in respiratory cilia. Analyses of both primary cells from individuals carrying TTC12 mutations and human differentiated airway cells invalidated for TTC12 by a CRISPR-Cas9 approach revealed an IDA defect restricted to a subset of single-headed IDAs that are different in flagella and cilia, whereas TTC12 depletion in the ciliate Paramecium tetraurelia recapitulated the sperm phenotype. Overall, our study, which identifies TTC12 as a gene involved in PCD, unveils distinct dynein assembly mechanisms in human motile cilia versus flagella.

Primary ciliary dyskinesia gene contribution in Tunisia: Identification of a major Mediterranean allele.

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous disease of motile cilia. Even though PCD is widely studied, North-African patients have been rarely explored. In this study, we aim at confirming the clinical diagnosis and explore the genetic spectrum of PCD in a cohort of Tunisian patients. Forty clinically diagnosed patients with PCD belonging to 34 families were recruited from Tunisian pediatric departments. In each proband, targeted capture PCD panel sequencing of the 40 PCD genes was performed. PCD panel sequencing identified bi-allelic mutations in 82% of the families in eight PCD genes. Remarkably, 23.5% of patients carried the same c.2190del CCDC39 mutation. Single nucleotide polymorphism profiling in six unrelated patients carrying this mutation has revealed a founder effect in North-African patients. This mutation is estimated to date back at least 1,400-1,750 years ago. The identification of this major allele allowed us to suggest a cost-effective genetic diagnostic strategy in North-African patients with PCD.

NLRP3-associated autoinflammatory diseases: Phenotypic and molecular characteristics of germline versus somatic mutations.

BACKGROUND: NLRP3-associated autoinflammatory diseases (NLRP3-AIDs) include conditions of various severities, due to germline or somatic mosaic NLRP3 mutations. OBJECTIVE: To identify mosaic- versus germline-specific NLRP3 mutations' characteristics, we reinterpreted all the mutations reported in NLRP3-AIDs and performed an in-depth study of 3 novel patients. METHODS: The pathogenicity of all reported mosaic/germline mutations was reassessed according to international recommendations and their location on the NLRP3 3-dimensional structure. Deep-targeted sequencing and NLRP3-inflammasome-activation assays were used to identify the disease-causing mutation in 3 patients. RESULTS: We identified, in 3 patients, mosaic mutations affecting the same NLRP3 amino acid (Glu569). This residue belongs to 1 of the 2 mosaic mutational hot spots that face each other in the core of the NLRP3 ATPase domain. The review of the 90 NLRP3 mutations identified in 277 patients revealed that those hot spots account for 68.5% of patients (37 of 54) with mosaic mutations. Glu569 is affected in 22% of the patients (12 of 54) with mosaic mutations and in 0.4% of patients (1 of 223) with germline mutations. Only 8 of 90 mutations were found in mosaic and germinal states. All of the germline mutations were associated with a severe phenotype. These data suggest that mutations found only in mosaic state could be incompatible with life if present in germinal state. None of the 5 most frequent germline mutations was identified in mosaic state. Mutations found only in germinal state could, therefore, be asymptomatic in mosaic state. CONCLUSIONS: The phenotypic spectrum of NLRP3-AIDs appears to be related to the germinal/mosaic status and localization of the underlying mutations.

Deep phenotyping, including quantitative ciliary beating parameters, and extensive genotyping in primary ciliary dyskinesia.

BACKGROUND: Primary ciliary dyskinesia (PCD) is a rare genetic disorder resulting in abnormal ciliary motility/structure, extremely heterogeneous at genetic and ultrastructural levels. We aimed, in light of extensive genotyping, to identify specific and quantitative ciliary beating anomalies, according to the ultrastructural phenotype. METHODS: We prospectively included 75 patients with PCD exhibiting the main five ultrastructural phenotypes (n=15/group), screened all corresponding PCD genes and measured quantitative beating parameters by high-speed video-microscopy (HSV). RESULTS: Sixty-eight (91%) patients carried biallelic mutations. Combined outer/inner dynein arms (ODA/IDA) defect induces total ciliary immotility, regardless of the gene involved. ODA defect induces a residual beating with dramatically low ciliary beat frequency (CBF) related to increased recovery stroke and pause durations, especially in case of DNAI1 mutations. IDA defect with microtubular disorganisation induces a low percentage of beating cilia with decreased beating angle and, in case of CCDC39 mutations, a relatively conserved mean CBF with a high maximal CBF. Central complex defect induces nearly normal beating parameters, regardless of the gene involved, and a gyrating motion in a minority of ciliated edges, especially in case of RSPH1 mutations. PCD with normal ultrastructure exhibits heterogeneous HSV values, but mostly an increased CBF with an extremely high maximal CBF. CONCLUSION: Quantitative HSV analysis in PCD objectives beating anomalies associated with specific ciliary ultrastructures and genotypes. It represents a promising approach to guide the molecular analyses towards the best candidate gene(s) to be analysed or to assess the pathogenicity of the numerous sequence variants identified by next-generation-sequencing.

Somatic Mosaic NLRP3 Mutations and Inflammasome Activation in Late-Onset Chronic Urticaria.

Chronic urticaria is a common skin disorder with heterogeneous causes. In the absence of physical triggers, chronic urticarial rash is called idiopathic or spontaneous. The objective of this study was to identify the molecular and cellular bases of a disease condition displayed by two unrelated patients aged over 60 years who presented for two decades with a chronic urticaria resistant to standard therapy that occurred in the context of systemic inflammation not triggered by cold. In both patients, a targeted sequencing approach using a next generation technology identified somatic mosaic mutations in NLRP3, a gene encoding a key inflammasome component. The study of several of both patients' cell types showed that, despite the late onset of the disease, NLRP3 mutations were not found to be restricted to myelomonocytic cells. Rather, the data obtained strongly suggested that the mutational event occurred very early, during embryonic development. As shown by functional studies, the identified mutations-an in-frame deletion and a recurrent NLRP3 missense mutation-have a gain-of-function effect on NLRP3-inflammasome activation. Consistently, a complete remission was obtained in both patients with anti-IL-1 receptor antagonists. This study unveils that in late-onset chronic urticaria, the search for autoinflammatory markers and somatic mosaic NLRP3 mutations may have important diagnostic and therapeutic consequences.

The NLRP3 p.A441V Mutation in NLRP3-AID Pathogenesis: Functional Consequences, Phenotype-Genotype Correlations and Evidence for a Recurrent Mutational Event.

OBJECTIVE: To determine the molecular and cellular bases of autoinflammatory syndromes in a multigenerational French family with Muckle-Wells syndrome and in a patient originating from Portugal with familial cold autoinflammatory syndrome. METHODS: Sequencing of NLRP3 exon 3 was performed in all accessible patients. Microsatellite and whole-genome single nucleotide polymorphism genotyping was used i) to test the intrafamilial segregation of the identified variant and ii) to look for a founder effect. Functional analyses included the study of i) apoptosis-associated speck-like protein containing a CARD (ASC) speck formation in HEK293T cells (stably expressing ASC-green fluorescent protein and pro-caspase 1-FLAG) transiently expressing the wild-type or mutated NLRP3 protein, ii) levels of IL-1ß secreted from transfected THP-1 cells, and iii) inflammasome-related gene expression and cytokine secretion from monocytes isolated from patients in crisis (probands from the two families), related patients out of crisis, and from controls. RESULTS: The same heterozygous mutation (c.1322C>T, p.A441V) located in the NACHT domain, segregating with the disease within the first family, was identified in the two families. This mutation was found to be associated with different core haplotypes. NLRP3-A441V led to increased ASC speck formation and high levels of secreted IL-1ß. Monocyte inflammasome-related gene expression and cytokine secretion, which were within the normal range in patients out of crisis, were found to be differentially regulated between the two probands, correlating with their phenotypic status. CONCLUSION: These molecular and cellular findings, which indicate a recurrent mutational event, clearly demonstrate the pathogenicity of the p.A441V missense mutation in NLRP3-associated autoinflammatory disease and point to the interest of studying patients' primary cells to assess disease activity.

Mutations in DNAH17, Encoding a Sperm-Specific Axonemal Outer Dynein Arm Heavy Chain, Cause Isolated Male Infertility Due to Asthenozoospermia.

Motile cilia and sperm flagella share an evolutionarily conserved axonemal structure. Their structural and/or functional defects are associated with primary ciliary dyskinesia (PCD), a genetic disease characterized by chronic respiratory-tract infections and in which most males are infertile due to asthenozoospermia. Among the well-characterized axonemal protein complexes, the outer dynein arms (ODAs), through ATPase activity of their heavy chains (HCs), play a major role for cilia and flagella beating. However, the contribution of the different HCs (γ-type: DNAH5 and DNAH8 and ß-type: DNAH9, DNAH11, and DNAH17) in ODAs from both organelles is unknown. By analyzing five male individuals who consulted for isolated infertility and displayed a loss of ODAs in their sperm cells but not in their respiratory cells, we identified bi-allelic mutations in DNAH17. The isolated infertility phenotype prompted us to compare the protein composition of ODAs in the sperm and ciliary axonemes from control individuals. We show that DNAH17 and DNAH8, but not DNAH5, DNAH9, or DNAH11, colocalize with α-tubulin along the sperm axoneme, whereas the reverse picture is observed in respiratory cilia, thus explaining the phenotype restricted to sperm cells. We also demonstrate the loss of function associated with DNAH17 mutations in two unrelated individuals by performing immunoblot and immunofluorescence analyses on sperm cells; these analyses indicated the absence of DNAH17 and DNAH8, whereas DNAH2 and DNALI, two inner dynein arm components, were present. Overall, this study demonstrates that mutations in DNAH17 are responsible for isolated male infertility and provides information regarding ODA composition in human spermatozoa.

X-linked primary ciliary dyskinesia due to mutations in the cytoplasmic axonemal dynein assembly factor PIH1D3.

By moving essential body fluids and molecules, motile cilia and flagella govern respiratory mucociliary clearance, laterality determination and the transport of gametes and cerebrospinal fluid. Primary ciliary dyskinesia (PCD) is an autosomal recessive disorder frequently caused by non-assembly of dynein arm motors into cilia and flagella axonemes. Before their import into cilia and flagella, multi-subunit axonemal dynein arms are thought to be stabilized and pre-assembled in the cytoplasm through a DNAAF2-DNAAF4-HSP90 complex akin to the HSP90 co-chaperone R2TP complex. Here, we demonstrate that large genomic deletions as well as point mutations involving PIH1D3 are responsible for an X-linked form of PCD causing disruption of early axonemal dynein assembly. We propose that PIH1D3, a protein that emerges as a new player of the cytoplasmic pre-assembly pathway, is part of a complementary conserved R2TP-like HSP90 co-chaperone complex, the loss of which affects assembly of a subset of inner arm dyneins.

Contribution of LHX4 Mutations to Pituitary Deficits in a Cohort of 417 Unrelated Patients.

Context: LHX4 encodes a LIM-homeodomain transcription factor that is implicated in early pituitary development. In humans, only 13 heterozygous LHX4 mutations have been associated with congenital hypopituitarism. Objective: The aims of this study were to evaluate the prevalence of LHX4 mutations in patients with hypopituitarism, to define the associated phenotypes, and to characterize the functional impact of the identified variants and the respective role of the 2 LIM domains of LHX4. Design and Patients: We screened 417 unrelated patients with isolated growth hormone deficiency or combined pituitary hormone deficiency associated with ectopic posterior pituitary and/or sella turcica anomalies for LHX4 mutations (Sanger sequencing). In vitro studies were performed to assess the functional consequences of the identified variants. Results: We identified 7 heterozygous variations, including p.(Tyr131*), p.(Arg48Thrfs*104), c.606+1G>T, p.Arg65Val, p.Thr163Pro, p.Arg221Gln, and p.Arg235Gln), that were associated with variable expressivity; 5 of the 7 were also associated with incomplete penetrance. The p.(Tyr131*), p.(Arg48Thrfs*104), p.Ala65Val, p.Thr163Pro, and p.Arg221Gln LHX4 variants are unable to transactivate the POU1F1 and GH promoters. As suggested by transactivation, subcellular localization, and protein-protein interaction studies, p.Arg235Gln is probably a rare polymorphism. Coimmunoprecipitation studies identified LHX3 as a potential protein partner of LHX4. As revealed by functional studies of LIM-defective recombinant LHX4 proteins, the LIM1 and LIM2 domains are not redundant. Conclusion: This study, performed in the largest cohort of patients screened so far for LHX4 mutations, describes 6 disease-causing mutations that are responsible for congenital hypopituitarism. LHX4 mutations were found to be associated with variable expressivity, and most of them with incomplete penetrance; their contribution to pituitary deficits that are associated with an ectopic posterior pituitary and/or a sella turcica defect is ∼1.4% in the 417 probands tested.

Mutations in DNAJB13, Encoding an HSP40 Family Member, Cause Primary Ciliary Dyskinesia and Male Infertility.

Primary ciliary dyskinesia (PCD) is an autosomal-recessive disease due to functional or ultra-structural defects of motile cilia. Affected individuals display recurrent respiratory-tract infections; most males are infertile as a result of sperm flagellar dysfunction. The great majority of the PCD-associated genes identified so far encode either components of dynein arms (DAs), which are multiprotein-ATPase complexes essential for ciliary motility, or proteins involved in DA assembly. To identify the molecular basis of a PCD phenotype characterized by central complex (CC) defects but normal DA structure, a phenotype found in ∼15% of cases, we performed whole-exome sequencing in a male individual with PCD and unexplained CC defects. This analysis, combined with whole-genome SNP genotyping, identified a homozygous mutation in DNAJB13 (c.833T>G), a gene encoding a HSP40 co-chaperone whose ortholog in the flagellated alga Chlamydomonas localizes to the radial spokes. In vitro studies showed that this missense substitution (p.Met278Arg), which involves a highly conserved residue of several HSP40 family members, leads to protein instability and triggers proteasomal degradation, a result confirmed by the absence of endogenous DNAJB13 in cilia and sperm from this individual. Subsequent DNAJB13 analyses identified another homozygous mutation in a second family; the study of DNAJB13 transcripts obtained from airway cells showed that this mutation (c.68+1G>C) results in a splicing defect consistent with a loss-of-function mutation. Overall, this study, which establishes mutations in DNAJB13 as a cause of PCD, unveils the key role played by DNAJB13 in the proper formation and function of ciliary and flagellar axonemes in humans.

Familial autoinflammation with neutrophilic dermatosis reveals a regulatory mechanism of pyrin activation.

Pyrin responds to pathogen signals and loss of cellular homeostasis by forming an inflammasome complex that drives the cleavage and secretion of interleukin-1ß (IL-1ß). Mutations in the B30.2/SPRY domain cause pathogen-independent activation of pyrin and are responsible for the autoinflammatory disease familial Mediterranean fever (FMF). We studied a family with a dominantly inherited autoinflammatory disease, distinct from FMF, characterized by childhood-onset recurrent episodes of neutrophilic dermatosis, fever, elevated acute-phase reactants, arthralgia, and myalgia/myositis. The disease was caused by a mutation in MEFV, the gene encoding pyrin (S242R). The mutation results in the loss of a 14-3-3 binding motif at phosphorylated S242, which was not perturbed by FMF mutations in the B30.2/SPRY domain. However, loss of both S242 phosphorylation and 14-3-3 binding was observed for bacterial effectors that activate the pyrin inflammasome, such as Clostridium difficile toxin B (TcdB). The S242R mutation thus recapitulated the effect of pathogen sensing, triggering inflammasome activation and IL-1ß production. Successful therapy targeting IL-1ß has been initiated in one patient, resolving pyrin-associated autoinflammation with neutrophilic dermatosis. This disease provides evidence that a guard-like mechanism of pyrin regulation, originally identified for Nod-like receptors in plant innate immunity, also exists in humans.

Mutations in GAS8, a Gene Encoding a Nexin-Dynein Regulatory Complex Subunit, Cause Primary Ciliary Dyskinesia with Axonemal Disorganization.

Primary ciliary dyskinesia (PCD) is an autosomal recessive disease characterized by chronic respiratory infections of the upper and lower airways, hypofertility, and, in approximately half of the cases, situs inversus. This complex phenotype results from defects in motile cilia and sperm flagella. Among the numerous genes involved in PCD, very few-including CCDC39 and CCDC40-carry mutations that lead to a disorganization of ciliary axonemes with microtubule misalignment. Focusing on this particular phenotype, we identified bi-allelic loss-of-function mutations in GAS8, a gene that encodes a subunit of the nexin-dynein regulatory complex (N-DRC) orthologous to DRC4 of the flagellated alga Chlamydomonas reinhardtii. Unlike the majority of PCD patients, individuals with GAS8 mutations have motile cilia, which, as documented by high-speed videomicroscopy, display a subtle beating pattern defect characterized by slightly reduced bending amplitude. Immunofluorescence studies performed on patients' respiratory cilia revealed that GAS8 is not required for the proper expression of CCDC39 and CCDC40. Rather, mutations in GAS8 affect the subcellular localization of another N-DRC subunit called DRC3. Overall, this study, which identifies GAS8 as a PCD gene, unveils the key importance of the corresponding protein in N-DRC integrity and in the proper alignment of axonemal microtubules in humans.

Germline SFTPA1 mutation in familial idiopathic interstitial pneumonia and lung cancer.

Idiopathic interstitial pneumonias (IIPs) comprise a heterogeneous group of rare lung parenchyma disorders with high morbidity and mortality, which can occur at all ages. In adults, the most common form of IIPs, idiopathic pulmonary fibrosis (IPF), has been associated with an increased frequency of lung cancer. The molecular basis of IIPs remains unknown in most cases. This study investigates IIP pathophysiology in 12 families affected by IPF and lung cancer. We identified, in a multigenerational family, nine members carrying a heterozygous missense mutation with evidence of pathogenicity in SFTPA1 that encodes the surfactant protein (SP)-A1. The mutation (p.Trp211Arg), which segregates with a disease phenotype characterized by either isolated IIP/IPF, or IPF associated with lung adenocarcinoma, is located in the carbohydrate recognition domain (CRD) of SP-A1 and involves a residue invariant throughout evolution, not only in SP-A1, but also in its close paralog SP-A2 and other CRD-containing proteins. As shown through functional studies, the p.Trp211Arg mutation impairs SP-A1 secretion. Immunohistochemistry studies on patient alveolar epithelium showed an altered SP-A expression pattern. Overall, this first report of a germline molecular defect in SFTPA1 unveils the key role of SP-A1 in the occurrence of several chronic respiratory diseases, ranging from severe respiratory insufficiency occurring early in life to the association of lung fibrosis and cancer in adult patients. These data also clearly show that, in spite of their structural and functional similarities, SP-A1 and SP-A2 are not redundant.