Wide phenotypic variability in RSPH9-associated primary ciliary dyskinesia: review of a case-series from Cyprus

Analyses of 1236 genotyped primary ciliary dyskinesia individuals identify regional clusters of distinct DNA variants and significant genotype-phenotype correlations

BACKGROUND

Primary ciliary dyskinesia (PCD) represents a group of rare hereditary disorders characterised by deficient ciliary airway clearance that can be associated with laterality defects. We aimed to describe the underlying gene defects, geographical differences in genotypes and their relationship to diagnostic findings and clinical phenotypes.

METHODS

Genetic variants and clinical findings (age, sex, body mass index, laterality defects, forced expiratory volume in 1 s (FEV1)) were collected from 19 countries using the European Reference Network's ERN-LUNG international PCD Registry. Genetic data were evaluated according to American College of Medical Genetics and Genomics guidelines. We assessed regional distribution of implicated genes and genetic variants as well as genotype correlations with laterality defects and FEV1.

RESULTS

The study included 1236 individuals carrying 908 distinct pathogenic DNA variants in 46 PCD genes. We found considerable variation in the distribution of PCD genotypes across countries due to the presence of distinct founder variants. The prevalence of PCD genotypes associated with pathognomonic ultrastructural defects (mean 72%, range 47-100%) and laterality defects (mean 42%, range 28-69%) varied widely among countries. The prevalence of laterality defects was significantly lower in PCD individuals without pathognomonic ciliary ultrastructure defects (18%). The PCD cohort had a reduced median FEV1 z-score (-1.66). Median FEV1 z-scores were significantly lower in CCNO (-3.26), CCDC39 (-2.49) and CCDC40 (-2.96) variant groups, while the FEV1 z-score reductions were significantly milder in DNAH11 (-0.83) and ODAD1 (-0.85) variant groups compared to the whole PCD cohort.

CONCLUSION

This unprecedented multinational dataset of DNA variants and information on their distribution across countries facilitates interpretation of the genetic epidemiology of PCD and indicates that the genetic variant can predict diagnostic and phenotypic features such as the course of lung function.

Primary Ciliary Dyskinesia: A Clinical Review

Primary ciliary dyskinesia (PCD) is a rare, genetically heterogeneous, motile ciliopathy, characterized by neonatal respiratory distress, recurrent upper and lower respiratory tract infections, subfertility, and laterality defects. Diagnosis relies on a combination of tests for confirmation, including nasal nitric oxide (nNO) measurements, high-speed videomicroscopy analysis (HSVMA), immunofluorescent staining, axonemal ultrastructure analysis via transmission electron microscopy (TEM), and genetic testing. Notably, there is no single gold standard confirmatory or exclusionary test. Currently, 54 causative genes involved in cilia assembly, structure, and function have been linked to PCD; this rare disease has a spectrum of clinical manifestations and emerging genotype-phenotype relationships. In this review, we provide an overview of the structure and function of motile cilia, the emerging genetics and pathophysiology of this rare disease, as well as clinical features associated with motile ciliopathies, novel diagnostic tools, and updates on genotype-phenotype relationships in PCD.

Practical guide for the diagnosis and management of primary ciliary dyskinesia

OBJECTIVE

Primary ciliary dyskinesia (PCD) is a relatively rare genetic disorder that affects approximately 1 in 20,000 people. Approximately 50 genes are currently known to cause PCD. In light of differences in causative genes and the medical system in Japan compared with other countries, a practical guide was needed for the diagnosis and management of Japanese PCD patients.

METHODS

An ad hoc academic committee was organized under the Japanese Rhinologic Society to produce a practical guide, with participation by committee members from several academic societies in Japan. The practical guide including diagnostic criteria for PCD was approved by the Japanese Rhinologic Society, Japanese Society of Otolaryngology-Head and Neck Surgery, Japanese Respiratory Society, and Japanese Society of Pediatric Pulmonology.

RESULTS

The diagnostic criteria for PCD consist of six clinical features, six laboratory findings, differential diagnosis, and genetic testing. The diagnosis of PCD is categorized as definite, probable, or possible PCD based on a combination of the four items above. Diagnosis of definite PCD requires exclusion of cystic fibrosis and primary immunodeficiency, at least one of the six clinical features, and a positive result for at least one of the following: (1) Class 1 defect on electron microscopy of cilia, (2) pathogenic or likely pathogenic variants in a PCD-related gene, or (3) impairment of ciliary motility that can be repaired by correcting the causative gene variants in iPS cells established from the patient's peripheral blood cells.

CONCLUSION

This practical guide provides clinicians with useful information for the diagnosis and management of PCD in Japan.

A splice donor variant of GAS8 induces structural disorganization of the axoneme in sperm flagella and leads to nonsyndromic male infertility

Motile cilia and flagella are closely related organelles structured around a highly conserved axoneme whose formation and maintenance involve proteins from hundreds of genes. Defects in many of these genes have been described to induce primary ciliary dyskinesia (PCD) mainly characterized by chronic respiratory infections, situs inversus and/or infertility. In men, cilia/flagella-related infertility is usually caused by asthenozoospermia due to multiple morphological abnormalities of the sperm flagella (MMAF). Here, we investigated a cohort of 196 infertile men displaying a typical MMAF phenotype without any other PCD symptoms. Analysis of WES data identified a single case carrying a deleterious homozygous GAS8 variant altering a splice donor consensus site. This gene, also known as DRC4, encodes a subunit of the Nexin-Dynein Regulatory Complex (N-DRC), and has been already associated to male infertility and mild PCD. Confirming the deleterious effect of the candidate variant, GAS8 staining by immunofluorescence did not evidence any signal from the patient's spermatozoa whereas a strong signal was present along the whole flagella length in control cells. Concordant with its role in the N-DRC, transmission electron microscopy evidenced peripheral microtubule doublets misalignments. We confirm here the importance of GAS8 in the N-DRC and observed that its absence induces a typical MMAF phenotype not necessarily accompanied by other PCD symptoms.

First reports of primary ciliary dyskinesia caused by a shared DNAH11 allele in Canadian Inuit

BACKGROUND

Primary ciliary dyskinesia (PCD) is typically an autosomal recessive disease characterized by recurrent infections of the lower respiratory tract, frequent and severe otitis media, chronic rhinosinusitis, neonatal respiratory distress, and organ laterality defects. While severe lower respiratory tract infections and bronchiectasis are common in Inuit, PCD has not been recognized in this population.

METHODS

We report a case series of seven Inuit patients with PCD identified by genetic testing in three Canadian PCD centers.

RESULTS

Patients ranged from 4 to 59 years of age (at time of last evaluation) and originated in the Qikiqtaaluk region (Baffin Island, n = 5), Nunavut, or Nunavik (northern Quebec, n = 2), Canada. They had typical features of PCD, including neonatal respiratory distress (five patients), situs inversus totalis (four patients), bronchiectasis (four patients), chronic atelectasis (six patients), and chronic otitis media (six patients). Most had chronic rhinitis. Genetic evaluation demonstrated that all had homozygous pathogenic variants in DNAH11 at NM_001277115.1:c.4095+2C>A.

CONCLUSIONS

The discovery of this homozygous DNAH11 variant in widely disparate parts of the Nunangat (Inuit homelands) suggests this is a founder mutation that may be widespread in Inuit. Thus, PCD may be an important cause of chronic lung, sinus, and middle ear disease in this population. Inuit with chronic lung disease, including bronchiectasis or laterality defects, should undergo genetic testing for PCD. Consideration of including PCD genetic analysis in routine newborn screening should be considered in Inuit regions.

Schmidtea mediterranea as a Model Organism to Study the Molecular Background of Human Motile Ciliopathies

Cilia and flagella are evolutionarily conserved organelles that form protrusions on the surface of many growth-arrested or differentiated eukaryotic cells. Due to the structural and functional differences, cilia can be roughly classified as motile and non-motile (primary). Genetically determined dysfunction of motile cilia is the basis of primary ciliary dyskinesia (PCD), a heterogeneous ciliopathy affecting respiratory airways, fertility, and laterality. In the face of the still incomplete knowledge of PCD genetics and phenotype-genotype relations in PCD and the spectrum of PCD-like diseases, a continuous search for new causative genes is required. The use of model organisms has been a great part of the advances in understanding molecular mechanisms and the genetic basis of human diseases; the PCD spectrum is not different in this respect. The planarian model (Schmidtea mediterranea) has been intensely used to study regeneration processes, and-in the context of cilia-their evolution, assembly, and role in cell signaling. However, relatively little attention has been paid to the use of this simple and accessible model for studying the genetics of PCD and related diseases. The recent rapid development of the available planarian databases with detailed genomic and functional annotations prompted us to review the potential of the S. mediterranea model for studying human motile ciliopathies.

Observational study of health utilities in adult primary ciliary dyskinesia patients: preliminary data on associations with molecular diagnosis, clinical phenotype and HRQOL measures

Background

Primary ciliary dyskinesia (PCD) is a congenital disorder characterized by chronic respiratory morbidity. To date, there is no information on PCD-specific preference-based quality of life measures such as health utilities (HU). We cross-sectionally assessed HU in adult PCD patients and explored relationships with genotype, phenotype and quality of life (QOL)-PCD scales.

Methods

Diagnostic testing was performed according to international guidelines, while participants completed the visual analog scale (VAS), time trade off (TTO), standard gamble (SG), and EuroQol 5 dimensions (EQ5D) HU instruments, as well as the QOL-PCD questionnaire. Hierarchical regression was used to identify the QOL-PCD scales that are most predictive of HU.

Results

Among 31 patients, median HU are 0.75 (VAS), 0.86 (EQ5D), 0.91 (TTO) and 0.99 (SG). The underlying genotype is not associated with HU measures. VAS and EQ5D are associated with lung function, while TTO and SG values are not sensitive to any of the examined factors. Among the QOL-PCD scales, physical functioning and lower respiratory symptoms explained much of VAS (R²= 0.419) and EQ5D (R²= 0.538) variability.

Conclusions

Our study demonstrates that HU elicitation in PCD is feasible using both direct and indirect methods. Overall, HU scores are relatively high among adult patients, with higher scores observed in SG and TTO, followed by EQ5D and VAS. VAS and EQ5D HU values are sensitive to lung function as well as to QOL-PCD physical functioning and lower respiratory symptom scores.

Limitations of Nasal Nitric Oxide Measurement for Diagnosis of Primary Ciliary Dyskinesia with Normal Ultrastructure

Rationale Primary ciliary dyskinesia (PCD) is a heterogeneous, multisystem disorder characterized by defective ciliary beating. Diagnostic guidelines of the American Thoracic Society (ATS) and European Respiratory Society (ERS) recommend measurement of nasal nitric oxide (nNO) for PCD diagnosis. Several studies demonstrated low nNO-production rates in PCD individuals but underlying causes remain elusive. Objective To determine nNO-production rates in a well-characterized PCD cohort including subgroup analyses with regard to ultrastructural and ciliary beating phenotypes. Methods This study included 301 individuals assessed according to ERS guidelines. Diagnostic cutoffs for nNO-production rates for this study cohort and subgroups with normal and abnormal ultrastructure were determined. Diagnostic accuracy was also tested for the widely used 77 nl/min-cutoff in this study cohort. The relationship between nNO-production rates and ciliary beat frequencies (CBFs) was evaluated. Results The study cohort comprised 180 individuals with definite PCD diagnosis including 160 individuals with genetic diagnosis, 16 individuals with probable PCD diagnosis and 105 disease controls. The 77 nl/min nNO-cutoff showed a test sensitivity of 0.92 and specificity of 0.86. Test sensitivity was lower (0.85) in the subgroup of 47 PCD individuals with normal ultrastructure compared to 133 PCD individuals with abnormal ultrastructure (0.95). The optimal diagnostic cutoff for the nNO-production rate for the whole study cohort was 69.8 nl/min (sensitivity 0.92, specificity 0.89), however it was 107.8 nl/min (sensitivity 0.89, specificity 0.78) for the subgroup of PCD with normal ultrastructure. PCD individuals with normal ultrastructure compared to abnormal ultrastructure showed higher ciliary motility. Consistently, PCD individuals with higher CBFs showed higher nNO-production rates. In addition, laterality defects occurred less frequently in PCD with normal ultrastructure. Conclusion Measurements of nNO below the widely used 77 nL/min cutoff are less sensitive in detecting PCD individuals with normal ultrastructure. Our findings indicate, that higher nNO-production in this subgroup with a higher cutoff for the nNO-production rate (107.8 nl/min) and higher residual ciliary motility are dependent on the underlying molecular PCD defect. Higher nNO-production rates, higher residual CBFs and the lower prevalence of laterality defects hamper diagnosis of PCD with normal ultrastructure. Adjusting the cutoff of nNO-production rate to 107.8 nl/min might promote diagnosing PCD with normal ultrastructure.

Genetic Regulation of Cytokine Response in Patients with Acute Community-Acquired Pneumonia

Background: Community-acquired pneumonia (CAP) is an acute disease condition with a high risk of rapid deteriorations. We analysed the influence of genetics on cytokine regulation to obtain a better understanding of patient’s heterogeneity. Methods: For up to N = 389 genotyped participants of the PROGRESS study of hospitalised CAP patients, we performed a genome-wide association study of ten cytokines IL-1β, IL-6, IL-8, IL-10, IL-12, MCP-1 (MCAF), MIP-1α (CCL3), VEGF, VCAM-1, and ICAM-1. Consecutive secondary analyses were performed to identify independent hits and corresponding causal variants. Results: 102 SNPs from 14 loci showed genome-wide significant associations with five of the cytokines. The most interesting associations were found at 6p21.1 for VEGF (p = 1.58 × 10⁻²⁰), at 17q21.32 (p = 1.51 × 10⁻⁹) and at 10p12.1 (p = 2.76 × 10⁻⁹) for IL-1β, at 10p13 for MIP-1α (CCL3) (p = 2.28 × 10⁻⁹), and at 9q34.12 for IL-10 (p = 4.52 × 10⁻⁸). Functionally plausible genes could be assigned to the majority of loci including genes involved in cytokine secretion, granulocyte function, and cilial kinetics. Conclusion: This is the first context-specific genetic association study of blood cytokine concentrations in CAP patients revealing numerous biologically plausible candidate genes. Two of the loci were also associated with atherosclerosis with probable common or consecutive pathomechanisms.

Emerging Genotype-Phenotype Relationships in Primary Ciliary Dyskinesia

Primary ciliary dyskinesia (PCD) is a rare inherited condition affecting motile cilia and leading to organ laterality defects, recurrent sino-pulmonary infections, bronchiectasis, and severe lung disease. Research over the past twenty years has revealed variability in clinical presentations, ranging from mild to more severe phenotypes. Genotype and phenotype relationships have emerged. The increasing availability of genetic panels for PCD continue to redefine these genotype-phenotype relationships and reveal milder forms of disease that had previously gone unrecognized.

Implementation of multigene panel NGS diagnosis in the national primary ciliary dyskinesia cohort of Cyprus: An island with a high disease prevalence

We aimed to determine a genetic diagnosis in the national primary ciliary dyskinesia (PCD) cohort of Cyprus, an island with a high disease prevalence. We used targeted next-generation sequencing (NGS) of 39 PCD genes in 48 patients of Greek-Cypriot and other ancestries. We achieved a molecular diagnosis in 74% of the unrelated families tested. We identified 24 different mutations in 11 genes, 12 of which are novel. Homozygosity was more common in Greek-Cypriot than non-Greek-Cypriot patients (88% vs. 46.2%, p = .016). Four mutations (DNAH11:c.5095-2A>G, CFAP300:c.95_103delGCCGGCTCC, TTC25:c.716G>A, RSPH9:c.670+2T>C) were found in 74% of the diagnosed Greek-Cypriot families. Patients with RSPH9 mutations demonstrated higher nasal nitric oxide (57 vs. 15 nl/min, p <.001), higher forced expiratory volume in 1 s (-0.89 vs. -2.37, p = .018) and forced vital capacity (-1.00 vs. -2.16, p = .029) z scores than the rest of the cohort. Targeted multigene-panel NGS is an efficient tool for early diagnosis of PCD, providing insight into genetic disease epidemiology and improved patient stratification.

A novel genetic variant in DNAI2 detected by custom gene panel in a newborn with Primary Ciliary Dyskinesia: case report

BACKGROUND

Primary ciliary dyskinesia (PCD) is a highly heterogeneous genetic disorder caused by defects in motile cilia. The hallmark features of PCD are the chronic infections of the respiratory tract, moreover, clinical manifestations include also laterality defects and risk of male infertility. Clinical phenotypes of PCD are the result of mutations in genes encoding components of axonema or factors involved in axonemal assembly. Recent studies have identified over 45 PCD-associated genes, therefore, molecular analysis represents a powerful diagnostic tool to confirm and uncover new genetic causes of this rare disease.

CASE PRESENTATION

Here, we describe a female infant of Moroccan origin with normal pressure hydrocephalus (NPH) in addition to most common PCD symptoms. Transmission Electron Microscopy (TEM) and molecular tests, such as a Next generation Sequencing panel and a custom array CGH, were performed for diagnosis of PCD. TEM revealed outer dynein arm (ODA) defects, whilst molecular analyses detected a novel 6,9 kb microdeletion in DNAI2 gene.

CONCLUSIONS

Since DNAI2 mutations are very rare, this case report contributes to better delineate the important role of DNAI2 as causative of PCD phenotype, suggesting, furthermore, that the variations in DNAI2 may be as a new genetic risk factor for NPH. Indeed, although the association of hydrocephalus with PCD has been well documented, however, only a small number of human patients show this defect. Furthermore, this study highlights the importance of high-throughput technologies in advancing our understanding of heterogeneous genetic disorders.

Loss of Rsph9 causes neonatal hydrocephalus with abnormal development of motile cilia in mice

Hydrocephalus is a brain disorder triggered by cerebrospinal fluid accumulation in brain cavities. Even though cerebrospinal fluid flow is known to be driven by the orchestrated beating of the bundled motile cilia of ependymal cells, little is known about the mechanism of ciliary motility. RSPH9 is increasingly becoming recognized as a vital component of radial spokes in ciliary "9 + 2" ultrastructure organization. Here, we show that deletion of the Rsph9 gene leads to the development of hydrocephalus in the early postnatal period. However, the neurodevelopment and astrocyte development are normal in embryonic Rsph9^-/- mice. The tubular structure of the central aqueduct was comparable in Rsph9^-/- mice. Using high-speed video microscopy, we visualized lower beating amplitude and irregular rotation beating pattern of cilia bundles in Rsph9^-/- mice compared with that of wild-type mice. And the centriolar patch size was significantly increased in Rsph9^-/- cells. TEM results showed that deletion of Rsph9 causes little impact in ciliary axonemal organization but the Rsph9^-/- cilia frequently had abnormal ectopic ciliary membrane inclusions. In addition, hydrocephalus in Rsph9^-/- mice results in the development of astrogliosis, microgliosis and cerebrovascular abnormalities. Eventually, the ependymal cells sloughed off of the lateral wall. Our results collectively suggested that RSPH9 is essential for ciliary structure and motility of mouse ependymal cilia, and its deletion causes the pathogenesis of hydrocephalus.

Registries and collaborative studies for primary ciliary dyskinesia in Europe

Primary ciliary dyskinesia (PCD) is a rare inherited disease characterised by malfunctioning cilia leading to a heterogeneous clinical phenotype with many organ systems affected. There is a lack of data on clinical presentation, prognosis and effectiveness of treatments, making it mandatory to improve the scientific evidence base.

This article reviews the data resources that are available in Europe for clinical and epidemiological research in PCD, namely established national PCD registries and national cohort studies, plus two large collaborative efforts (the international PCD (iPCD) Cohort and the International PCD Registry), and discusses their strengths, limitations and perspectives.

Denmark, Cyprus, Norway and Switzerland have national population-based registries, while England and France conduct multicentre cohort studies. Based on the data contained in these registries, the prevalence of diagnosed PCD is 3–7 per 100 000 in children and 0.2–6 per 100 000 in adults. All registries, together with other studies from Europe and beyond, contribute to the iPCD Cohort, a collaborative study including data from over 4000 PCD patients, and to the International PCD Registry, which is part of the ERN (European Reference Network)-LUNG network.

This rich resource of readily available, standardised and contemporaneous data will allow obtaining fast answers to emerging clinical and research questions in PCD.

The growing collaborative network of national and international registries and cohort studies of patients with PCD provides an excellent resource for research on this rare diseasehttps://bit.ly/3dto75l

Rare Human Diseases: Model Organisms in Deciphering the Molecular Basis of Primary Ciliary Dyskinesia

Primary ciliary dyskinesia (PCD) is a recessive heterogeneous disorder of motile cilia, affecting one per 15,000-30,000 individuals; however, the frequency of this disorder is likely underestimated. Even though more than 40 genes are currently associated with PCD, in the case of approximately 30% of patients, the genetic cause of the manifested PCD symptoms remains unknown. Because motile cilia are highly evolutionarily conserved organelles at both the proteomic and ultrastructural levels, analyses in the unicellular and multicellular model organisms can help not only to identify new proteins essential for cilia motility (and thus identify new putative PCD-causative genes), but also to elucidate the function of the proteins encoded by known PCD-causative genes. Consequently, studies involving model organisms can help us to understand the molecular mechanism(s) behind the phenotypic changes observed in the motile cilia of PCD affected patients. Here, we summarize the current state of the art in the genetics and biology of PCD and emphasize the impact of the studies conducted using model organisms on existing knowledge.

The value of nasal nitric oxide measurement in the diagnosis of primary ciliary dyskinesia

IMPORTANCE

Nasal nitric oxide (nNO) testing is a method used in the diagnosis of primary ciliary dyskinesia (PCD). It has not been evaluated in Chinese population.

OBJECTIVE

To establish a reference nNO value to assist in the diagnosis of PCD in Chinese children.

METHODS

nNO values were measured in children with PCD (n = 36), cystic fibrosis (CF) (n = 20), asthma (n = 45), post-infectious bronchiolitis obliterans (BO) (n = 41) and non-PCD/non-CF bronchiectasis (n = 32). The receiver operating characteristic nNO value for the diagnosis of PCD was plotted and the area under the curve was calculated.

RESULTS

nNO values were significantly lower in children with PCD (median 25.66 nL/min) than in children with asthma (186.26 ± 58.95 nL/ min), BO (143.47 ± 49.71 nL/min) and non-PCD/non-CF bronchiectasis (173.13 ± 63.80 nL/min), but not in children with CF (90.90 ± 43.20 nL/min). Notably however, no CF patient had an nNO value < 45 nL/min. A cut-off of 76 nL/min yielded the best sensitivity of 86.1%, and specificity of 91.4%, with an area under the curve of 0.920 (95% confidence interval 0.859-0.981) for the diagnosis of PCD. If CF was ruled out the specificity increased to nearly 100%.

INTERPRETATION

nNO testing is able to discriminate between patients with PCD and those with CF, asthma, post-infectious BO and non-PCD/non-CF bronchiectasis. A cut-off of 76 nL/min could be further examined in patients suspected of PCD, to establish an nNO reference value for PCD screening in Chinese children.