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Primary ciliary dyskinesia (PCD) is predominantly an autosomal recessively inherited condition that affects ~1 in 15,000 people. Diagnosis of PCD can be complex and is ordinarily based on the results of multiple investigations. These investigations include nasal nitric oxide, high-speed video microscopy, genotyping, and electron microscopy analysis of ciliary ultrastructure. A diagnosis is ultimately confirmed by the presence of a hallmark defect identified by transmission electron microscopy or biallelic variants in a known PCD gene. Secondary ciliary defects are commonly seen in samples submitted for diagnosis of PCD. Acquired secondary ciliary ultrastructural abnormalities, which are not caused by a variant in a ciliary gene, are usually transient and reversible however failure to separate primary versus secondary defects can lead to misdiagnosis. In this review, we describe causes of secondary ciliary defects, identify the ultrastructural appearances associated with secondary ciliary dyskinesia and finally suggest methods to avoid misdiagnosis of PCD due to these acquired ciliary defects.

BackgroundPrimary ciliary dyskinesia (PCD), a genetically heterogeneous condition enriched in some consanguineous populations, results from recessive mutations affecting cilia biogenesis and motility. Currently, diagnosis requires multiple expert tests.MethodsThe diagnostic utility of multigene panel next-generation sequencing (NGS) was evaluated in 161 unrelated families from multiple population ancestries.ResultsMost (82%) families had affected individuals with biallelic or hemizygous (75%) or single (7%) pathogenic causal alleles in known PCD genes. Loss-of-function alleles dominate (73% frameshift, stop-gain, splice site), most (58%) being homozygous, even in non-consanguineous families. Although 57% (88) of the total 155 diagnostic disease variants were novel, recurrent mutations and mutated genes were detected. These differed markedly between white European (52% of families carry DNAH5 or DNAH11 mutations), Arab (42% of families carry CCDC39 or CCDC40 mutations) and South Asian (single LRRC6 or CCDC103 mutations carried in 36% of families) patients, revealing a striking genetic stratification according to population of origin in PCD. Genetics facilitated successful diagnosis of 81% of families with normal or inconclusive ultrastructure and 67% missing prior ultrastructure results.ConclusionsThis study shows the added value of high-throughput targeted NGS in expediting PCD diagnosis. Therefore, there is potential significant patient benefit in wider and/or earlier implementation of genetic screening.

Primary ciliary dyskinesia (PCD) is associated with abnormal organ positioning (situs) and congenital heart disease (CHD). This study investigated genotype–phenotype associations in PCD to facilitate risk predictions for cardiac and laterality defects. This retrospective cohort study of 389 UK patients with PCD found 51% had abnormal situs and 25% had CHD and/or laterality defects other than situs inversus totalis. Patients with biallelic mutations in a subset of nine PCD genes had normal situs. Patients with consanguineous parents had higher odds of situs abnormalities than patients with non-consanguineous parents. Patients with abnormal situs had higher odds of CHD and/or laterality defects.

International audience; Motile cilia move body fluids and gametes and the beating of cilia lining the airway epithelial surfaces ensures that they are kept clear and protected from inhaled pathogens and consequent respiratory infections. Dynein motor proteins provide mechanical force for cilia beating. Dynein mutations are a common cause of primary ciliary dyskinesia (PCD), an inherited condition characterized by deficient mucociliary clearance and chronic respiratory disease coupled with laterality disturbances and subfertility. Using next-generation sequencing, we detected mutations in the ciliary outer dynein arm (ODA) heavy chain gene DNAH9 in individuals from PCD clinics with situs inversus and in one case male infertility. DNAH9 and its partner heavy chain DNAH5 localize to type 2 ODAs of the distal cilium and in DNAH9-mutated nasal respiratory epithelial cilia we found a loss of DNAH9/DNAH5-containing type 2 ODAs that was restricted to the distal cilia region. This confers a reduced beating frequency with a subtle beating pattern defect affecting the motility of the distal cilia portion. 3D electron tomography ultrastructural studies confirmed regional loss of ODAs from the distal cilium, manifesting as either loss of whole ODA or partial loss of ODA volume. Paramecium DNAH9 knockdown confirms an evolutionarily conserved function for DNAH9 in cilia motility and ODA stability. We find that DNAH9 is widely expressed in the airways, despite DNAH9 mutations appearing to confer symptoms restricted to the upper respiratory tract. In summary, DNAH9 mutations reduce cilia function but some respiratory mucociliary clearance potential may be retained, widening the PCD disease spectrum.

International audience; Primary ciliary dyskinesia (PCD) is a genetically and phenotypically heterogeneous disorder characterized by destructive respiratory disease and laterality abnormalities due to randomized left-right body asymmetry. PCD is mostly caused by mutations affecting the core axoneme structure of motile cilia that is essential for movement. Genes that cause PCD when mutated include a group that encode proteins essential for the assembly of the ciliary dynein motors and the active transport process that delivers them from their cytoplasmic assembly site into the axoneme. We screened a cohort of affected individuals for disease-causing mutations using a targeted next generation sequencing panel and identified two unrelated families (three affected children) with mutations in the uncharacterized C11orf70 gene (official gene name CFAP300). The affected children share a consistent PCD phenotype from early life with laterality defects and immotile respiratory cilia displaying combined loss of inner and outer dynein arms (IDA+ODA). Phylogenetic analysis shows C11orf70 is highly conserved, distributed across species similarly to proteins involved in the intraflagellar transport (IFT)-dependant assembly of axonemal dyneins. Paramecium C11orf70 RNAi knockdown led to combined loss of ciliary IDA+ODA with reduced cilia beating and swim velocity. Tagged C11orf70 in Paramecium and Chlamydomonas localizes mainly in the cytoplasm with a small amount in the ciliary component. IFT139/TTC21B (IFT-A protein) and FLA10 (IFT kinesin) depletion experiments show that its transport within cilia is IFT dependent. During ciliogenesis, C11orf70 accumulates at the ciliary tips in a similar distribution to the IFT-B protein IFT46. In summary, C11orf70 is essential for assembly of dynein arms and C11orf70 mutations cause defective cilia motility and PCD.

RationalePrimary ciliary dyskinesia is a genetically heterogeneous inherited condition characterised by progressive lung disease arising from abnormal cilia function. Approximately half of patients have situs inversus. The estimated prevalence of primary ciliary dyskinesia in the UK South Asian population is 1:2265. Early, accurate diagnosis is key to implementing appropriate management but clinical diagnostic tests can be equivocal.ObjectivesTo determine the importance of genetic screening for primary ciliary dyskinesia in a UK South Asian population with a typical clinical phenotype, where standard testing is inconclusive.MethodsNext-generation sequencing was used to screen 86 South Asian patients who had a clinical history consistent with primary ciliary dyskinesia. The effect of a CCDC103 p.His154Pro missense variant compared with other dynein arm-associated gene mutations on diagnostic/phenotypic variability was tested. CCDC103 p.His154Pro variant pathogenicity was assessed by oligomerisation assay.ResultsSixteen of 86 (19%) patients carried a homozygous CCDC103 p.His154Pro mutation which was found to disrupt protein oligomerisation. Variable diagnostic test results were obtained including normal nasal nitric oxide levels, normal ciliary beat pattern and frequency and a spectrum of partial and normal dynein arm retention. Fifteen (94%) patients or their sibling(s) had situs inversus suggesting CCDC103 p.His154Pro patients without situs inversus are missed.ConclusionsThe CCDC103 p.His154Pro mutation is more prevalent than previously thought in the South Asian community and causes primary ciliary dyskinesia that can be difficult to diagnose using pathology-based clinical tests. Genetic testing is critical when there is a strong clinical phenotype with inconclusive standard diagnostic tests.

Introduction Primary ciliary dyskinesia (PCD) is a heterogeneous, recessive disease, characterised by dysfunction of motile cilia that arises from structural defects. Symptoms include chronic pulmonary disease, rhinosinusitis, otitis media, laterality defects, congenital heart disease and subfertility. The most commonly affected cilia structure is the outer dynein arm (ODA), a complex structure composed of a docking complex and multiple heavy, light and intermediate dynein chains. An understanding of the relationship between the genetic and structural phenotype of ODA variants will allow patient stratification and improve diagnosis through verification of new candidate genes. Methods 195 PCD patients were genotyped using next generation sequencing. Candidate variants were confirmed by Sanger sequencing and familial segregation analysis. For selected ODA mutations, electron tomography, an extension to transmission electron microscopy, was used to produce high-resolution 3D models of ciliary axonemal microtubular doublets and ODA volume ratios. The data were analysed to determine the impact of eight different gene mutations causing different structural defects of the ODAs. Results 39% of patients had bi-allelic mutations identified which are associated with ODA structure. These include variants in known PCD genes: DNAH5 (n=39), DNAH11 (n=18), DNAI1 (n=8), DNAI2 (n=5), ARMC4 (n=3), CCDC114 (n=2), DNAL1 (n=1) and mutations in the novel candidate DNAH9. Variants in DNAH9 have been suggested as a cause of PCD previously but disregarded due to lack of phenotypic evidence. 3D models of the ODA complex identified genotype specific changes in the ODA complex in PCD. The ODA structure in PCD was different in the proximal region, in proximity to the microvili, when compared to the distal region, towards the tip of the axoneme. A significant deficiency in the ODA volume was detected at the distal part of the axoneme in the patient with DNAH9 defects, whereas the proximal portion was unaffected, reflecting the protein position of DNAH9. Conclusion 3D electron tomography can be used to detect subtle changes in the ultrastructure of the ODA in PCD patients with differences detected in the impact of mutations in proximal versus distal regions of the cilia.

Primary ciliary dyskinesia (PCD) is a genetically and phenotypically heterogeneous disorder characterized by destructive respiratory disease and laterality abnormalities due to randomised left-right body asymmetry. PCD is mostly caused by mutations affecting components of the core axoneme structure of motile cilia that are essential for cilia movement. In addition, there is a growing group of PCD genes that encode proteins essential for the assembly of the ciliary dynein motors and the active transport process that delivers them from their cytoplasmic assembly site into the axoneme. We screened a cohort of affected individuals for disease-causing mutations using a targeted next generation sequencing panel and identified 2 unrelated families (3 affected children) with mutations in the uncharacterized C11orf70 gene. The affected children share a consistent PCD phenotype from early life with laterality defects and immotile respiratory cilia displaying combined loss of inner and outer dynein arms (IDA+ODA). Phylogenetic analysis shows C11orf70 is highly conserved, distributed across species similarly to proteins involved in the intraflagellar transport (IFT)-dependant assembly of axonemal dyneins. Paramecium C11orf70 RNAi knockdown led to combined loss of ciliary IDA+ODA with reduced cilia beating and swim velocity. Fluorescently tagged C11orf70 in Paramecium and Chlamydomonas localises mainly in the cytoplasm with a small amount in the ciliary component, its abundance in the axoneme being IFT-dependant. During ciliogenesis, C11orf70 accumulates at the ciliary tips in a similar distribution to the IFT-B protein IFT46. In summary, C11orf70 is essential for IFT-dependant assembly of dynein arms and C11orf70 mutations cause defective cilia motility and PCD.

BACKGROUND Cilia line the surface of the respiratory tract and beat in a coordinated wave to protect the lungs against infection. Bardet Biedl Syndrome (BBS) is a rare condition attributed to cilia dysfunction. Murine models of BBS suggest a respiratory phenotype; however, no reports have studied the translation of these findings in patients. METHODS We assessed the clinical symptoms of motile cilia dysfunction and the histology of ciliated respiratory epithelium in patients with BBS. RESULTS We report an increased prevalence of neonatal respiratory distress at birth (12%), general practitioner-diagnosed asthma (21%), otitis media (33%), and rhinitis (36%) in patients with BBS. These symptoms, however, occurred at a significantly reduced prevalence compared with patients with known motile cilia dysfunction (primary ciliary dyskinesia). Respiratory epithelial assessment revealed cellular damage, significant ciliary depletion (on 60% of ciliated cells), and goblet cell hyperplasia in patients with BBS (50% goblet cells). These findings were quantifiably similar to those of patients with asthma ( P > .05). Surprisingly, motile cilia function and ultrastructure were grossly normal with the exception of occasional unique inclusions within the ciliary membrane. CONCLUSIONS In conclusion, motile ciliary structure and function are essentially normal in patients with BBS.

Primary Ciliary Dyskinesia (PCD) is a genetically heterogeneous condition where dysfunction of motile cilia results in chronic respiratory disease. Ciliary ultrastructure examined by Transmission Electron Microscopy (TEM) or biallelic mutations in a known PCD gene are usually used to confirm the diagnosis. However, 15-30% cases of PCD have apparently normal ciliary ultrastructure or no known genetic cause, making diagnosis difficult. Electron tomography, an extension of TEM, produces high resolution 3D ultrastructural reconstructions. We hypothesise that electron tomography can be performed on existing diagnostic material to detect ultrastructural abnormalities in patients with PCD and ‘normal ultrastructure’ and/or novel gene variants. Longitudinal and transverse sections of proximal cilia were examined from araldite embedded nasal brush biopsies. 14 patients with PCD and 6 healthy controls were studied. Dual axis tomograms were collected on a Jeol 1400+ TEM. The data were analysed and averaged using IMOD software. Electron tomography indicated deficiency in the outer dynein arm volume (n=7), absence of central pair projections (n=3) and partial absence of nexin link structures (n=3) in patients with PCD and previously reported ‘normal ultrastructure’. A subset of the inner dynein arms were shown to be missing in a patient previously reported as an IDA defect with a variant in the novel gene PIH1D3. Electron tomography performed on diagnostic samples is effective in visualising defects which are difficult to identify using conventional TEM. Tomography could be used with genotyping to confirm a diagnosis and to investigate new PCD genes.

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous condition characterised by progressive lung disease arising from abnormal motile ciliary function. Approximately half of patients have situs inversus. The estimated prevalence of PCD in the UK South Asian population is 1:2,265. Early, accurate diagnosis is key to implementing appropriate management but clinical diagnostic tests can be equivocal. The aim of this study was to determine the importance of genetic screening for primary ciliary dyskinesia in a UK South Asian population with a typical clinical phenotype, where standard testing is inconclusive. Next-generation sequencing was used to screen 86 South Asian patients who had a clinical history consistent with PCD. The effect of a CCDC103 c.461A>C p.His154Pro missense variant on phenotypic variability was tested and variant pathogenicity was assessed by oligomerisation assay. Sixteen of 86(19%) patients carried a homozygous CCDC103 p.His154Pro mutation which was found to disrupt protein oligomerisation. Variable diagnostic test results were obtained including normal nasal nitric oxide levels (7/15 patients tested), normal ciliary beat pattern or frequency (9/16 cases) and a spectrum of partial and normal dynein arm retention (9/16 cases). Fifteen (94%) patients or their sibling (s) had situs inversus suggesting in CCDC103 p.His154Pro patients without situs inversus the diagnosis is missed. In conclusion, the CCDC103 p.His154Pro mutation is more prevalent than previously thought in the South Asian community and causes PCD that can be difficult to diagnose using pathology-based clinical tests. Genetic testing is critical when there is a strong clinical phenotype with inconclusive or normal diagnostic tests

The standard approach to diagnosis of primary ciliary dyskinesia (PCD) in the United Kingdom consists of assessing ciliary function by high-speed microscopy and ultrastructure by election microscopy, but equipment and expertise is not widely available internationally. The identification of biallelic disease-causing mutations is also diagnostic, but many disease-causing genes are unknown, and testing is not widely available outside the United States. Fluorescent antibodies to ciliary proteins are used to validate research genetic studies, but diagnostic utility in this disease has not been systematically evaluated.To determine utility of a panel of six fluorescent labeled antibodies as a diagnostic tool for PCD.The study used immunofluorescent labeling of nasal brushings from a discovery cohort of 35 patients diagnosed with PCD by ciliary ultrastructure, and a diagnostic accuracy cohort of 386 patients referred with symptoms suggestive of disease. The results were compared with diagnostic outcome.Immunofluorescence correctly identified mislocalized or absent staining in 100% of the discovery cohort. In the diagnostic cohort immunofluorescence successfully identified 22 of 25 patients with PCD and normal staining in all 252 in whom PCD was considered highly unlikely. In addition, immunofluorescence provided a result in 55% (39) of cases that were previously inconclusive. Immunofluorescence results were available within 14 days, costing $187 per sample compared with electron microscopy (27 days; cost $1,452).Immunofluorescence is a highly specific diagnostic test for PCD, and it improves the speed and availability of diagnostic testing. However, sensitivity is limited and immunofluorescence is not suitable as a stand-alone test.

Primary ciliary dyskinesia is an autosomal recessive disorder affecting the motility of cilia. There are a range of ultrastructural ciliary defects that lead to associated clinical symptoms including ineffective mucus clearance, reduced lung function, infertility, and left-right isomerism. Mutations in radial spoke head proteins are a known cause of primary ciliary dyskinesia. Ultrastructually these defects are identified by a portion of cilia lacking a central pair and transposed outer microtubular doublets. We have repeatedly observed an intermittent loss of the central pair in patients with a transposition defect. To further understand the central pair changes in these radial spoke head mutations we employ electron tomography, a high resolution electron microscope technique, to elucidate in three dimensions the ultrastructural arrangements caused by mutation of the RSPH4A gene. We thereby provide an explanation of the structures observed by conventional electron microscopy studies. We demonstrate that the central pair can be present within the cilium. In some cilia, the central pair rotates at the base of the axoneme. We propose that it is this rotation that gives rise to an intermittent appearance of the central pair when viewed under conventional electron microscopy. We discuss the potential causes and consequences of these findings. © 2014 Wiley Periodicals, Inc.

Background The examination of ciliary ultrastructure in a nasal sample remains a definitive diagnostic test for primary ciliary dyskinesia (PCD). Methods The quantitative assessment of ciliary ultrastructure in the diagnosis of PCD over a 20-year period was reviewed. Results During this period, 1182 patients were referred for ciliary ultrastructural analysis, 242 (20%) of whom were confirmed as having the disease. The two main causes of PCD identified were a lack of outer dynein arms (43%) and a lack of both inner and outer dynein arms (24%). Other causes included transposition, radial spoke and inner dynein arm defects. No specific ultrastructural defects were detected in 33 patients (3%) diagnosed as having PCD on the basis of their clinical features and screening tests that included a low nasal nitric oxide concentration or slow saccharine clearance and abnormal ciliary beat frequency or pattern. Conclusions Electron microscopy analysis can confirm but does not always exclude a diagnosis of PCD.

In primary ciliary dyskinesia (PCD), motile ciliary dysfunction arises from ciliary defects usually confirmed by transmission electron microscopy (TEM). In 30% of patients, such as those with DNAH11 mutations, apparently normal ultrastructure makes diagnosis difficult. Genetic analysis supports diagnosis, but may not identify definitive causal variants. Electron tomography, an extension of TEM, produces three-dimensional ultrastructural ciliary models with superior resolution to TEM. Our hypothesis is that tomography using existing patient samples will enable visualisation of DNAH11-associated ultrastructural defects. Dual axis tomograms from araldite-embedded nasal cilia were collected in 13 PCD patients with normal ultrastructure (DNAH11 n=7, HYDIN n=2, CCDC65 n=3 and DRC1 n=1) and six healthy controls, then analysed using IMOD and Chimera software.DNAH11 protein is localised to the proximal ciliary region. Within this region, electron tomography indicated a deficiency of >25% of proximal outer dynein arm volume in all patients with DNAH11 mutations (n=7) compared to other patients with PCD and normal ultrastructure (n=6) and healthy controls (n=6). DNAH11 mutations cause a shared abnormality in ciliary ultrastructure previously undetectable by TEM. Advantageously, electron tomography can be used on existing diagnostic samples and establishes a structural abnormality where ultrastructural studies were previously normal.

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous inherited disorder arising from dysmotility of motile cilia and sperm. This is associated with a variety of ultrastructural defects of the cilia and sperm axoneme that affect movement, leading to clinical consequences on respiratory-tract mucociliary clearance and lung function, fertility, and left-right body-axis determination. We performed whole-genome SNP-based linkage analysis in seven consanguineous families with PCD and central-microtubular-pair abnormalities. This identified two loci, in two families with intermittent absence of the central-pair structure (chromosome 6p21.1, Zmax 6.7) and in five families with complete absence of the central pair (chromosome 6q22.1, Zmax 7.0). Mutations were subsequently identified in two positional candidate genes, RSPH9 on chromosome 6p21.1 and RSPH4A on chromosome 6q22.1. Haplotype analysis identified a common ancestral founder effect RSPH4A mutation present in UK-Pakistani pedigrees. Both RSPH9 and RSPH4A encode protein components of the axonemal radial spoke head. In situ hybridization of murine Rsph9 shows gene expression restricted to regions containing motile cilia. Investigation of the effect of knockdown or mutations of RSPH9 orthologs in zebrafish and Chlamydomonas indicate that radial spoke head proteins are important in maintaining normal movement in motile, “9+2”-structure cilia and flagella. This effect is rescued by reintroduction of gene expression for restoration of a normal beat pattern in zebrafish. Disturbance in function of these genes was not associated with defects in left-right axis determination in humans or zebrafish.

Cilia line the surface of the respiratory tract and beat in a coordinated wave to protect the lungs against infection. Bardet Biedl Syndrome (BBS) is a rare condition attributed to cilia dysfunction. Murine models of BBS suggest a respiratory phenotype; however, no reports have studied the translation of these findings in patients.We assessed the clinical symptoms of motile cilia dysfunction and the histology of ciliated respiratory epithelium in patients with BBS.We report an increased prevalence of neonatal respiratory distress at birth (12%), general practitioner-diagnosed asthma (21%), otitis media (33%), and rhinitis (36%) in patients with BBS. These symptoms, however, occurred at a significantly reduced prevalence compared with patients with known motile cilia dysfunction (primary ciliary dyskinesia). Respiratory epithelial assessment revealed cellular damage, significant ciliary depletion (on 60% of ciliated cells), and goblet cell hyperplasia in patients with BBS (50% goblet cells). These findings were quantifiably similar to those of patients with asthma (P.05). Surprisingly, motile cilia function and ultrastructure were grossly normal with the exception of occasional unique inclusions within the ciliary membrane.In conclusion, motile ciliary structure and function are essentially normal in patients with BBS.

Primary Ciliary Dyskinesia (PCD) is a genetically heterogeneous condition. characterised by impaired mucociliary clearance and chronic sino-pulmonary disease. Over 30 causative gene mutations resulting in dysfunctional ciliary motility and structure have been identified. Ciliary ultrastructure examined by Transmission Electron Microscopy (TEM) is currently the diagnostic gold standard. Patients with mutations in the gene DNAH11 have a hyperfrequent ciliary beat and clinical symptoms of PCD. Diagnosis of a DNAH11 defect by TEM is difficult due to apparently normal ciliary ultrastructure. The electron tomography technique, an extension of TEM, produces 3D models of cilia with superior resolution. The aim of this study was to determine if electron tomography can detect ultrastructural abnormalities in patients with DNAH11 defects. Immunofluorescence by specific antibodies for DNAH11 showed localisation to the proximal portion of cilia. Proximal cilia cross sections from araldite embedded nasal brush biopsies were examined. Dual axis tomograms were collected on a Philips CM200 electron microscope. The data were analysed using IMOD software and averaged using PEET. Electron tomography and averaging of cilia cross sections indicated a deficiency in the outer dynein arm, consistent across all patients with a DNAH11 defect (n = 5) compared to healthy controls (n = 3) and patients with PCD due to a defect of the central pair or nexin link (n = 3) (Figure 1). A reduction in outer dynein arm volume of 30% was identified compared to healthy and PCD controls. In conclusion, a mutation in DNAH11 results in a subtle abnormality in ultrastructure. The defects are specific to the ‘forearm’ of the outer dynein arm and only detectable at the base of the cilium where DNAH11 is located. Electron tomography is highly effective in visualising this defect.

Primary ciliary dyskinesia is an autosomal recessive disorder affecting the motility of cilia. There are a range of ultrastructural ciliary defects that lead to associated clinical symptoms including ineffective mucus clearance, reduced lung function, infertility, and left-right isomerism. Mutations in radial spoke head proteins are a known cause of primary ciliary dyskinesia. Ultrastructually these defects are identified by a portion of cilia lacking a central pair and transposed outer microtubular doublets. We have repeatedly observed an intermittent loss of the central pair in patients with a transposition defect. To further understand the central pair changes in these radial spoke head mutations we employ electron tomography, a high resolution electron microscope technique, to elucidate in three dimensions the ultrastructural arrangements caused by mutation of the RSPH4A gene. We thereby provide an explanation of the structures observed by conventional electron microscopy studies. We demonstrate that the central pair can be present within the cilium. In some cilia, the central pair rotates at the base of the axoneme. We propose that it is this rotation that gives rise to an intermittent appearance of the central pair when viewed under conventional electron microscopy. We discuss the potential causes and consequences of these findings. © 2014 Wiley Periodicals, Inc.

Primary ciliary dyskinesia (PCD) is a genetic condition in which there is a defect in cilia motility. This can be caused by the absence of the inner dynein arm motor (IDA). The IDA can be difficult to observe by electron microscopy and has been shown to transiently disappear, making accurate diagnosis difficult. This study reviewed cases of PCD due to an IDA defect on the Royal Brompton Hospital database in order to confirm or retract the diagnosis. This was achieved using current methods of diagnosis (nasal nitric oxide, light and electron microscopy) and new techniques to improve visualisation of the IDA such as immunofluorescence analysis and 3D electron tomography. Four patients received normal results and the diagnosis of PCD was reversed. Three patients had another structural defect in combination with absence of IDAs. The remaining five patients had an absence of IDA in mean (SD) 42(22) % of their cilia. In these group diagnostic findings were heterogeneous with a diverse range of cilia beat pattern and frequencies. Immunofluorescent antibodies revealed the presence of the IDA component protein DNALI1 in all patients and high resolution electron tomography confirmed the presence of some IDA structures. Nasal nitric oxide values ranged from 3 to 463 ppb. In conclusion, PCD due to an IDA defect is difficult to diagnose as the IDA appears transiently absent on TEM. Diagnosis is reversed by repeat sampling in 38% patients. We suggest an isolated absence of IDA shown by TEM is not sufficient to confirm a diagnosis of PCD.

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous inherited disorder characterised by recurrent respiratory tract infections, bronchiectasis and subfertility which arises from cilia/sperm dysmotility associated with axonemal ultrastructural abnormalities. Laterality is randomized with ~50% of patients having situs inversus. Up to 15% of PCD cases show perturbation of the 9+2 microtubule structure and loss of the inner dynein arms, and these have tended to be referred to as ‘radial spoke defect’ cases. The radial spokes are essential for axoneme motility, mediating signal transduction between the central microtubular pair and dynein arm motors. Two genes causing this specific ultrastructural defect are known: CCDC39 (Merveille et. al., Nat Genet. 2011 43:72-8) and CCDC40 (Becker-Heck et. al. Nat Genet. 2011 43:79-84). We sequenced these genes in 22 PCD families with an ultrastructural defect involving microtubule disorganisation, either with or without accompanying loss of the inner dynein arms. We found recesively inherited CCDC39 mutations in 8/22 families and CCDC40 mutations in 7/22 families in the cohort, jointly accounting for a remarkable 68% (15/22) of families. The majority of CCDC39 and CCDC40 mutations were nonsense or frameshift resulting in early protein truncation, predicted to cause major disruption to the axoneme. Furthermore, there was a preponderance of homozygous mutations accounting for disease, even in families from outbred populations. Our results highlight the key role of the CCDC39 and CCDC40 genes in PCD with radial spoke defect, and suggest that disease is associated with complete protein loss (null alleles). These two genes represent prime targets for genetic testing in this disease phenotype. Work is in progress to identify the disease genes in the remaining patients within this subgroup, by next generation whole exome sequencing.

The ultrastructures of cilia and flagella are highly similar and well conserved through evolution. Consequently, Chlamydomonas is commonly used as a model organism for the study of human respiratory cilia. Since detailed models of Chlamydomonas axonemes were generated using cryoelectron tomography, disparities among some of the ultrastructural features have become apparent when compared with human cilia. Extrapolating information on human disease from the Chlamydomonas model may lead to discrepancies in translational research. This study aimed to establish the first three-dimensional ultrastructural model of human cilia. Tomograms of transverse sections (n = 6) and longitudinal sections (n = 9) of human nasal respiratory cilia were generated from three healthy volunteers. Key features of the cilium were resolved using subatomic averaging, and were measured. For validation of the method, a model of the well characterized structure of Chlamydomonas reinhardtii was simultaneously generated. Data were combined to create a fully quantified three-dimensional reconstruction of human nasal respiratory cilia. We highlight key differences in the axonemal sheath, microtubular doublets, radial spokes, and dynein arms between the two structures. We show a decreased axial periodicity of the radial spokes, inner dynein arms, and central pair protrusions in the human model. We propose that this first human model will provide a basis for research into the function and structure of human respiratory cilia in health and in disease.

Introduction and objectives Mutation type may affect clinical phenotype in PCD, as shown by differences in forced expiratory volume in 1 s (FEV 1 ) (AJRCCM 2015;191:316–324). LCI, measured using multi-breath washout (MBW) is raised in PCD (AJRCCM 2013;188:545–549) but the relative sensitivities of the two physiological measurements is disputed (Thorax 2015;70:339–345, and 305–306). We hypothesised that LCI would be more sensitive to genotype-phenotype differences in PCD. Methods MBW (using sulphur hexafluoride MBW with a photoacoustic gas analyser) and spirometry were performed in 77 PCD patients (mean age 16.4 years (range 4–62.2), 33 males, mean FEV 1 z score -2.09 (range - 5.33–1.59)). 44 had outer dynein arms (ODA) defects, or both inner (IDA) and ODA, 18 had microtubular defects (either transposition or microtubule disorganisation with absent IDA), 15 had normal ultrastructure (diagnosis made on either genetics (n = 10), low nasal NO, clinical phenotype and consistent dyskinesia on light microscopy (n = 1), or low nasal NO, clinical phenotype and an affected sibling (n = 3)). There was no significant difference in age or gender composition between the 3 groups. Results Patients with normal ultrastructure had significantly higher FEV 1 and lower LCI, indicating milder disease. Those with ODA +/- IDA had a more normal LCI than those with microtubular defects (Figure 1), but similar FEV 1 . Conclusions PCD patients with normal ultrastructure have the milder disease, and those with microtubular defects more severe. Differences were more apparent on LCI than FEV 1 , suggesting LCI may be more sensitive to worse distal small airway disease in PCD.

Motile cilia in the respiratory tract beat to clear mucus from the airways, keeping the lung clean and free from infection. In the inherited genetic condition Primary Ciliary Dyskinesia (PCD) cilia beat is ineffective, resulting in chronic cough, recurrent chest infections and rhinosinustitis. The definitive diagnostic test for PCD is electron microscopy of ciliary ultrastructure. There are a number of known ultrastructural defects associated with PCD. We have recently established the first three dimensional model of human respiratory cilia ultrastructure using electron tomography. Electron tomography is an electron microscopy technique which allows increased resolution and visualisation of structures in three dimensions. Our model highlights key features of the axoneme which cannot be resolved using traditional electron microscopy. The aim of this study was to characterise in 3D the ultrastructure of defects associated with PCD using the normal model as a template. Tomograms of transverse and longitudinal sections of cilia were generated from nasal brush biopsies taken from patients with PCD. Key features of the cilium were resolved using sub- volume or sub-tomographic averaging and measured. We show in detail the ultrastructural phenotype of radial spoke, dynein arm and central pair defects allowing insight into the structure of human respiratory tract cilium and primary ciliary dyskinesia.