Mutations in C11orf70 Cause Primary Ciliary Dyskinesia with Randomization of Left/Right Body Asymmetry Due to Defects of Outer and Inner Dynein Arms

A novel homozygous mutation of CFAP300 identified in a Chinese patient with primary ciliary dyskinesia and infertility

Primary ciliary dyskinesia (PCD) is a clinically rare, genetically and phenotypically heterogeneous condition characterized by chronic respiratory tract infections, male infertility, tympanitis, and laterality abnormalities. PCD is typically resulted from variants in genes encoding assembly or structural proteins that are indispensable for the movement of motile cilia. Here, we identified a novel nonsense mutation, c.466G>T, in cilia- and flagella-associated protein 300 (CFAP300) resulting in a stop codon (p.Glu156 *) through whole-exome sequencing (WES). The proband had a PCD phenotype with laterality defects and immotile sperm flagella displaying a combined loss of the inner dynein arm (IDA) and outer dynein arm (ODA). Bioinformatic programs predicted that the mutation is deleterious. Successful pregnancy was achieved through intracytoplasmic sperm injection (ICSI). Our results expand the spectrum of CFAP300 variants in PCD and provide reproductive guidance for infertile couples suffering from PCD caused by them.

Characterization of pathogenic genetic variants in Russian patients with primary ciliary dyskinesia using gene panel sequencing and transcript analysis

BACKGROUND

Primary ciliary dyskinesia (PCD) is a group of rare genetically heterogeneous disorders caused by defective cilia and flagella motility. The clinical phenotype of PCD patients commonly includes chronic oto-sino-pulmonary disease, infertility, and, in about half of cases, laterality defects due to randomization of left-right body asymmetry. To date, pathogenic variants in more than 50 genes responsible for motile cilia structure and assembly have been reported in such patients. While multiple population-specific mutations have been described in PCD cohorts from different countries, the data on genetic spectrum of PCD in Russian population are still extremely limited.

RESULTS

The present study provides a comprehensive clinical and genetic characterization of 21 Russian families with PCD living in various country regions. Anomalies of ciliary beating in patients` respiratory epithelial cells were confirmed by high-speed video microscopy. In the most cases, custom-designed panel sequencing allowed to uncover causative variants in well-known or rarely mentioned PCD-related genes, including DNAH5, DNAH11, CFAP300, LRRC6, ZMYND10, CCDC103, HYDIN, ODAD4, DNAL1, and OFD1. The variations comprised common mutations, as well as novel genetic variants, some of which probably specific for Russian patients. Additional targeted analysis of mRNA transcripts from ciliated cells enabled us to specify functional effects of newly identified genetic variants in DNAH5 (c.2052+3G>T, c.3599-2A>G), HYDIN (c.10949-2A>G, c.1797C>G), and ZMYND10 (c.510+1G>C) on splicing process. In particular, the splice site variant c.2052+3G>T, detected in four unrelated families, resulted in skipping of exon 14 in DNAH5 transcripts and, according to haplotype analysis of affected probands, was proposed as an ancestral founder mutation in Udmurt population.

CONCLUSIONS

The reported data provide a vital insight into genetic background of primary ciliary dyskinesia in the Russian population. The findings clearly illustrate the utility of gene panel sequencing coupled with transcriptional analysis in identification and clinical interpretation of novel genetic variants.

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.

A novel homozygous missense TTC12 variant identified in an infertile Pakistani man with severe oligoasthenoteratozoospermia and primary ciliary dyskinesia

TTC12 is a cytoplasmic and centromere-localized protein that plays a role in the proper assembly of dynein arm complexes in motile cilia in both respiratory cells and sperm flagella. This finding underscores its significance in cellular motility and function. However, the wide role of TTC12 in human spermatogenesis-associated primary ciliary dyskinesia (PCD) still needs to be elucidated. Whole-exome sequencing (WES) and Sanger sequencing were performed to identify potentially pathogenic variants causing PCD and multiple morphological abnormalities of sperm flagella (MMAF) in an infertile Pakistani man. Diagnostic imaging techniques were used for PCD screening in the patient. Real-time polymerase chain reaction (RT‒PCR) was performed to detect the effect of mutations on the mRNA abundance of the affected genes. Papanicolaou staining and scanning electron microscopy (SEM) were carried out to examine sperm morphology. Transmission electron microscopy (TEM) was performed to examine the ultrastructure of the sperm flagella, and the results were confirmed by immunofluorescence staining. Using WES and Sanger sequencing, a novel homozygous missense variant (c.C1069T; p.Arg357Trp) in TTC12 was identified in a patient from a consanguineous family. A computed tomography scan of the paranasal sinuses confirmed the symptoms of the PCD. RT-PCR showed a decrease in TTC12 mRNA in the patient's sperm sample. Papanicolaou staining, SEM, and TEM analysis revealed a significant change in shape and a disorganized axonemal structure in the sperm flagella of the patient. Immunostaining assays revealed that TTC12 is distributed throughout the flagella and is predominantly concentrated in the midpiece in normal spermatozoa. In contrast, spermatozoa from patient deficient in TTC12 showed minimal staining intensity for TTC12 or DNAH17 (outer dynein arms components). This could lead to MMAF and result in male infertility. This novel TTC12 variant not only illuminates the underlying genetic causes of male infertility but also paves the way for potential treatments targeting these genetic factors. This study represents a significant advancement in understanding the genetic basis of PCD-related infertility.

Mutations in CFAP47, a previously reported MMAF causative gene, also contribute to the respiratory defects in patients with PCD

BACKGROUND

Primary ciliary dyskinesia (PCD) is a genetic ciliopathy characterized by dysfunction of motile cilia. Currently, approximately 50 causative genes accounting for 60%-70% of all PCD cases have been identified in PCD-affected individuals, but the etiology in approximately 30%-40% of PCD cases remains unknown.

METHODS

We analyzed the clinical and genetic data of two PCD individuals who were suspected of having PCD. Whole-exome sequencing and Sanger sequencing were performed to identify and verify the variants in CFAP47. We also evaluated the expression of CFAP47 by real-time quantitative PCR and immunofluorescence. Transmission electron microscopy in respiratory epithelial cells was also conducted to analyze ciliary function.

RESULTS

Two hemizygous missense variants of X-linked CFAP47 in two unrelated PCD individuals were identified. The expression of CFAP47 in two PCD individuals was significantly reduced in vivo and in vitro assays. A reduction in the amount of epithelial ciliary cells and basal bodies from PCD individuals was also observed.

CONCLUSIONS

We describe two hemizygous missense variants of X-linked CFAP47 in two unrelated PCD individuals and prove CFAP47 variants are related to a reduced number of epithelial ciliary cells. Therefore, we suggest that CFAP47 should be known as a novel pathogenic gene of human PCD.

Pathogenic variants in CLXN encoding the outer dynein arm docking-associated calcium-binding protein calaxin cause primary ciliary dyskinesia

PURPOSE

Primary ciliary dyskinesia (PCD) is a heterogeneous disorder that includes respiratory symptoms, laterality defects, and infertility caused by dysfunction of motile cilia. Most PCD-causing variants result in abnormal outer dynein arms (ODAs), which provide the generative force for respiratory ciliary beating and proper mucociliary clearance.

METHODS

In addition to studies in mouse and planaria, clinical exome sequencing and functional analyses in human were performed.

RESULTS

In this study, we identified homozygous pathogenic variants in CLXN (EFCAB1/ODAD5) in 3 individuals with laterality defects and respiratory symptoms. Consistently, we found that Clxn is expressed in mice left-right organizer. Transmission electron microscopy depicted ODA defects in distal ciliary axonemes. Immunofluorescence microscopy revealed absence of CLXN from the ciliary axonemes, absence of the ODA components DNAH5, DNAI1, and DNAI2 from the distal axonemes, and mislocalization or absence of DNAH9. In addition, CLXN was undetectable in ciliary axonemes of individuals with defects in the ODA-docking machinery: ODAD1, ODAD2, ODAD3, and ODAD4. Furthermore, SMED-EFCAB1-deficient planaria displayed ciliary dysmotility.

CONCLUSION

Our results revealed that pathogenic variants in CLXN cause PCD with defects in the assembly of distal ODAs in the respiratory cilia. CLXN should be referred to as ODA-docking complex-associated protein ODAD5.

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.

Identification of novel biallelic LRRC6 variants in male Chinese patients with primary ciliary dyskinesia and infertility

PURPOSE

The aim of this study is to identify the genetic cause of primary ciliary dyskinesia (PCD) and male infertility in two unrelated Han Chinese families.

METHODS

We performed whole-exome sequencing in two unrelated male Han Chinese patients suffering from infertility and PCD to identify the pathogenic variants. Ultrastructural and immunostaining analyses of patient's spermatozoa were performed to characterize the effect of the variants. The pathogenicity of the variants was validated using patient's spermatozoa by western blotting and immunostaining analysis. Intracytoplasmic sperm injection (ICSI) was conducted in the affected families.

RESULTS

Three variants in leucine-rich repeat containing 6 (LRRC6) [patient 1(compound heterozygote): NM_012472: c.538C > T, (p.R180*) and c.64dupT, (p.S22Ffs*19); patient 2 (homozygote): c.863C > A, (p.P288H)] were identified in two unrelated patients with PCD and male infertility. These variants were predicated deleterious and were absent or rare in human population genome data. LRRC6-mutant spermatozoa showed a highly aberrant morphology and ultrastructure with lacked inner and outer dynein arms. The LRRC6 protein was present along the normal sperm flagella, and was significantly decreased in the mutated spermatozoa. Interestingly, both patients were able to conceive through ICSI and birthed a healthy baby.

CONCLUSION

Our results extend the LRRC6 variant spectrum and provide reproductive guidance to families suffering from PCD-linked infertility caused by LRRC6 variants.

Pathogenic gene variants in CCDC39, CCDC40, RSPH1, RSPH9, HYDIN, and SPEF2 cause defects of sperm flagella composition and male infertility

Primary Ciliary Dyskinesia (PCD) is a rare genetic disorder affecting the function of motile cilia in several organ systems. In PCD, male infertility is caused by defective sperm flagella composition or deficient motile cilia function in the efferent ducts of the male reproductive system. Different PCD-associated genes encoding axonemal components involved in the regulation of ciliary and flagellar beating are also reported to cause infertility due to multiple morphological abnormalities of the sperm flagella (MMAF). Here, we performed genetic testing by next generation sequencing techniques, PCD diagnostics including immunofluorescence-, transmission electron-, and high-speed video microscopy on sperm flagella and andrological work up including semen analyses. We identified ten infertile male individuals with pathogenic variants in CCDC39 (one) and CCDC40 (two) encoding ruler proteins, RSPH1 (two) and RSPH9 (one) encoding radial spoke head proteins, and HYDIN (two) and SPEF2 (two) encoding CP-associated proteins, respectively. We demonstrate for the first time that pathogenic variants in RSPH1 and RSPH9 cause male infertility due to sperm cell dysmotility and abnormal flagellar RSPH1 and RSPH9 composition. We also provide novel evidence for MMAF in HYDIN- and RSPH1-mutant individuals. We show absence or severe reduction of CCDC39 and SPEF2 in sperm flagella of CCDC39- and CCDC40-mutant individuals and HYDIN- and SPEF2-mutant individuals, respectively. Thereby, we reveal interactions between CCDC39 and CCDC40 as well as HYDIN and SPEF2 in sperm flagella. Our findings demonstrate that immunofluorescence microscopy in sperm cells is a valuable tool to identify flagellar defects related to the axonemal ruler, radial spoke head and the central pair apparatus, thus aiding the diagnosis of male infertility. This is of particular importance to classify the pathogenicity of genetic defects, especially in cases of missense variants of unknown significance, or to interpret HYDIN variants that are confounded by the presence of the almost identical pseudogene HYDIN2.

CFAP300 mutation causing primary ciliary dyskinesia in Finland

Primary ciliary dyskinesia (PCD) is a rare genetic condition characterized by chronic respiratory tract infections and in some cases laterality defects and infertility. The symptoms of PCD are caused by malfunction of motile cilia, hair-like organelles protruding out of the cell that are responsible for removal of mucus from the airways and organizing internal organ positioning during embryonic development. PCD is caused by mutations in genes coding for structural or assembly proteins in motile cilia. Thus far mutations in over 50 genes have been identified and these variants explain around 70% of all known cases. Population specific genetics underlying PCD has been reported, thus highlighting the importance of characterizing gene variants in different populations for development of gene-based diagnostics. In this study, we identified a recurrent loss-of-function mutation c.198_200delinsCC in CFAP300 causing lack of the protein product. PCD patients homozygous for the identified CFAP300 mutation have immotile airway epithelial cilia associated with missing dynein arms in their ciliary axonemes. Furthermore, using super resolution microscopy we demonstrate that CFAP300 is transported along cilia in normal human airway epithelial cells suggesting a role for CFAP300 in dynein complex transport in addition to preassembly in the cytoplasm. Our results highlight the importance of CFAP300 in dynein arm assembly and improve diagnostics of PCD in Finland.

FBB18 participates in preassembly of almost all axonemal dyneins independent of R2TP complex

Assembly of dynein arms requires cytoplasmic processes which are mediated by dynein preassembly factors (DNAAFs). CFAP298, which is conserved in organisms with motile cilia, is required for assembly of dynein arms but with obscure mechanisms. Here, we show that FBB18, a Chlamydomonas homologue of CFAP298, localizes to the cytoplasm and functions in folding/stabilization of almost all axonemal dyneins at the early steps of dynein preassembly. Mutation of FBB18 causes no or short cilia accompanied with partial loss of both outer and inner dynein arms. Comparative proteomics using 15N labeling suggests partial degradation of almost all axonemal dynein heavy chains (DHCs). A mutant mimicking a patient variant induces particular loss of DHCα. FBB18 associates with 9 DNAAFs and 14 out of 15 dynein HCs but not with IC1/IC2. FBB18 interacts with RuvBL1/2, components of the HSP90 co-chaperone R2TP complex but not the holo-R2TP complex. Further analysis suggests simultaneous formation of multiple DNAAF complexes involves dynein folding/stability and thus provides new insights into axonemal dynein preassembly.

The role of SPAG1 in the assembly of axonemal dyneins in human airway epithelia

Mutations in SPAG1, a dynein axonemal assembly factor (DNAAF) that facilitates the assembly of dynein arms in the cytoplasm before their transport into the cilium, result in primary ciliary dyskinesia (PCD), a genetically heterogenous disorder characterized by chronic oto-sino-pulmonary disease, infertility and laterality defects. To further elucidate the role of SPAG1 in dynein assembly, we examined its expression, interactions and ciliary defects in control and PCD human airway epithelia. Immunoprecipitations showed that SPAG1 interacts with multiple DNAAFs, dynein chains and canonical components of the R2TP complex. Protein levels of dynein heavy chains (DHCs) and interactions between DHCs and dynein intermediate chains (DICs) were reduced in SPAG1 mutants. We also identified a previously uncharacterized 60 kDa SPAG1 isoform, through examination of PCD subjects with an atypical ultrastructural defect for SPAG1 variants, that can partially compensate for the absence of full-length SPAG1 to assemble a reduced number of outer dynein arms. In summary, our data show that SPAG1 is necessary for axonemal dynein arm assembly by scaffolding R2TP-like complexes composed of several DNAAFs that facilitate the folding and/or binding of the DHCs to the DIC complex.

Primary ciliary dyskinesia in Volendam: Diagnostic and phenotypic features in patients with a CCDC114 mutation

Primary ciliary dyskinesia (PCD) is a heterogeneous disease, with impaired mucociliary clearance causing respiratory tract infections. A founding CCDC114 mutation has led to a relatively homogeneous and large Dutch PCD population in Volendam. Our aim was to describe their phenotype. Therefore, all Volendam PCD patients seen at the Amsterdam UMC were included in this study. Data were collected on lung function, microbiology, radiology, and ear‐nose‐throat (ENT) symptoms. A mixed effects model estimated lung function decline in %point per year (95% confidence interval [CI]). Thirty‐three (60%) out of approximately 56 Volendam PCD patients were treated at our center and included in this study. Only 30% of patients had situs inversus. FEV₁ declined in children (−1.43%/year, CI: −1.80/−1.05), but not in adults (0.01%/year, CI: −0.36/0.38). Pseudomonas aeruginosa was cultured in 21% of children and 60% of adults, respectively. Patients who have been infected at some point with P. aeruginosa had a steeper decline in FEV₁ as compared to patients that have never been infected. Neonatal symptoms (79%) and ENT problems (94%) were common; fertility issues however, were not (11%) common. Compared to other PCD cohorts, the Volendam/CCDC114 patients have a moderately severe phenotype with lung function decline predominantly occurring in childhood.

Respiratory symptoms of Swiss people with Primary Ciliary Dyskinesia

Background

Mostly derived from chart reviews, where symptoms are recorded in a nonstandardised manner, clinical data about primary ciliary dyskinesia (PCD) are inconsistent, which leads to missing and unreliable information. We assessed the prevalence and frequency of respiratory and ear symptoms and studied differences by age and sex among an unselected population of Swiss people with PCD.

Methods

We sent a questionnaire that included items from the FOLLOW-PCD standardised questionnaire to all Swiss PCD registry participants.

Results

We received questionnaires from 74 (86%) out of 86 invited persons or their caregivers (median age 23 years, range 3–73 years), including 68% adults (≥18 years) and 51% females. Among participants, 70 (94%) reported chronic nasal symptoms; most frequently runny nose (65%), blocked nose (55%) or anosmia (38%). Ear pain and hearing problems were reported by 58% of the participants. Almost all (99%) reported cough and sputum production. The most common chronic cough complications were gastro-oesophageal reflux (n=11; 15%), vomiting (n=8; 11%) and urinary incontinence (n=6; 8%). Only nine (12%) participants reported frequent wheeze, which occurred mainly during infection or exercise, while 49 (66%) reported shortness of breath, and 9% even at rest or during daily activities. Older patients reported more frequent nasal symptoms and shortness of breath. We found no difference by sex or ultrastructural ciliary defect.

Conclusion

This is the first study to describe patient-reported PCD symptoms. The consistent collection of standardised clinical data will allow us to better characterise the phenotypic variability of the disease and study disease course and prognosis.

Detailed information about patient-reported PCD symptoms will help characterise the phenotypic variability of the disease and could inform the development of individualised treatment strategies for patientshttps://bit.ly/363Zb4T

PCD Genes-From Patients to Model Organisms and Back to Humans

Primary ciliary dyskinesia (PCD) is a hereditary genetic disorder caused by the lack of motile cilia or the assembxly of dysfunctional ones. This rare human disease affects 1 out of 10,000-20,000 individuals and is caused by mutations in at least 50 genes. The past twenty years brought significant progress in the identification of PCD-causative genes and in our understanding of the connections between causative mutations and ciliary defects observed in affected individuals. These scientific advances have been achieved, among others, due to the extensive motile cilia-related research conducted using several model organisms, ranging from protists to mammals. These are unicellular organisms such as the green alga Chlamydomonas, the parasitic protist Trypanosoma, and free-living ciliates, Tetrahymena and Paramecium, the invertebrate Schmidtea, and vertebrates such as zebrafish, Xenopus, and mouse. Establishing such evolutionarily distant experimental models with different levels of cell or body complexity was possible because both basic motile cilia ultrastructure and protein composition are highly conserved throughout evolution. Here, we characterize model organisms commonly used to study PCD-related genes, highlight their pros and cons, and summarize experimental data collected using these models.

HPODNets: deep graph convolutional networks for predicting human protein-phenotype associations

MOTIVATION

Deciphering the relationship between human genes/proteins and abnormal phenotypes is of great importance in the prevention, diagnosis and treatment against diseases. The Human Phenotype Ontology (HPO) is a standardized vocabulary that describes the phenotype abnormalities encountered in human disorders. However, the current HPO annotations are still incomplete. Thus, it is necessary to computationally predict human protein-phenotype associations. In terms of current, cutting-edge computational methods for annotating proteins (such as functional annotation), three important features are (i) multiple network input, (ii) semi-supervised learning and (iii) deep graph convolutional network (GCN), whereas there are no methods with all these features for predicting HPO annotations of human protein.

RESULTS

We develop HPODNets with all above three features for predicting human protein-phenotype associations. HPODNets adopts a deep GCN with eight layers which allows to capture high-order topological information from multiple interaction networks. Empirical results with both cross-validation and temporal validation demonstrate that HPODNets outperforms seven competing state-of-the-art methods for protein function prediction. HPODNets with the architecture of deep GCNs is confirmed to be effective for predicting HPO annotations of human protein and, more generally, node label ranking problem with multiple biomolecular networks input in bioinformatics.

AVAILABILITY AND IMPLEMENTATION

https://github.com/liulizhi1996/HPODNets.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Current and Future Treatments in Primary Ciliary Dyskinesia

Primary ciliary dyskinesia (PCD) is a rare genetic ciliopathy in which mucociliary clearance is disturbed by the abnormal motion of cilia or there is a severe reduction in the generation of multiple motile cilia. Lung damage ensues due to recurrent airway infections, sometimes even resulting in respiratory failure. So far, no causative treatment is available and treatment efforts are primarily aimed at improving mucociliary clearance and early treatment of bacterial airway infections. Treatment guidelines are largely based on cystic fibrosis (CF) guidelines, as few studies have been performed on PCD. In this review, we give a detailed overview of the clinical studies performed investigating PCD to date, including three trials and several case reports. In addition, we explore precision medicine approaches in PCD, including gene therapy, mRNA transcript and read-through therapy.

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.

Ciliary Dyneins and Dynein Related Ciliopathies

Although ubiquitously present, the relevance of cilia for vertebrate development and health has long been underrated. However, the aberration or dysfunction of ciliary structures or components results in a large heterogeneous group of disorders in mammals, termed ciliopathies. The majority of human ciliopathy cases are caused by malfunction of the ciliary dynein motor activity, powering retrograde intraflagellar transport (enabled by the cytoplasmic dynein-2 complex) or axonemal movement (axonemal dynein complexes). Despite a partially shared evolutionary developmental path and shared ciliary localization, the cytoplasmic dynein-2 and axonemal dynein functions are markedly different: while cytoplasmic dynein-2 complex dysfunction results in an ultra-rare syndromal skeleto-renal phenotype with a high lethality, axonemal dynein dysfunction is associated with a motile cilia dysfunction disorder, primary ciliary dyskinesia (PCD) or Kartagener syndrome, causing recurrent airway infection, degenerative lung disease, laterality defects, and infertility. In this review, we provide an overview of ciliary dynein complex compositions, their functions, clinical disease hallmarks of ciliary dynein disorders, presumed underlying pathomechanisms, and novel developments in the field.

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.

Identification of a frame shift mutation in the CCDC151 gene in a Han-Chinese family with Kartagener syndrome

Kartagener syndrome (KS), a subtype of primary ciliary dyskinesia (PCD), is characterized by bronchiectasis, chronic sinusitis, male infertility and situs inversus. KS is a genetically heterogeneous disease that is inherited in an autosomal recessive form; however, X-linked inheritance has also been reported. As of this writing [late 2020], at least 34 loci, most of which have known genes, have been reported in the literature as associating with KS. In the present study, we identified a frame shift mutation, c.167delG (p.G56Dfs*26), in the coiled-coil domain containing 151 gene (CCDC151) responsible for KS in a Han-Chinese family. To our knowledge, this is the first report of a CCDC151 c.167delG mutation in the KS patient. These findings may expand the CCDC151 mutation spectrum of KS, and contribute to future genetic counseling and gene-targeted therapy for this disease.

Limitations and opportunities in the pharmacotherapy of ciliopathies

Ciliopathies are a family of rather diverse conditions, which have been grouped based on the finding of altered or dysfunctional cilia, potentially motile, small cellular antennae extending from the surface of postmitotic cells. Cilia-related disorders include embryonically arising conditions such as Joubert, Usher or Kartagener syndrome, but also afflictions with a postnatal or even adult onset phenotype, i.e. autosomal dominant polycystic kidney disease. The majority of ciliopathies are syndromic rather than affecting only a single organ due to cilia being found on almost any cell in the human body. Overall ciliopathies are considered rare diseases. Despite that, pharmacological research and the strive to help these patients has led to enormous therapeutic advances in the last decade. In this review we discuss new treatment options for certain ciliopathies, give an outlook on promising future therapeutic strategies, but also highlight the limitations in the development of therapeutic approaches of ciliopathies.

Motility of efferent duct cilia aids passage of sperm cells through the male reproductive system

Motile cilia line the efferent ducts of the mammalian male reproductive tract. Several recent mouse studies have demonstrated that a reduced generation of multiple motile cilia in efferent ducts is associated with obstructive oligozoospermia and fertility issues. However, the sole impact of efferent duct cilia dysmotility on male infertility has not been studied so far either in mice or human. Using video microscopy, histological- and ultrastructural analyses, we examined male reproductive tracts of mice deficient for the axonemal motor protein DNAH5: this defect exclusively disrupts the outer dynein arm (ODA) composition of motile cilia but not the ODA composition and motility of sperm flagella. These mice have immotile efferent duct cilia that lack ODAs, which are essential for ciliary beat generation. Furthermore, they show accumulation of sperm in the efferent duct. Notably, the ultrastructure and motility of sperm from these males are unaffected. Likewise, human individuals with loss-of-function DNAH5 mutations present with reduced sperm count in the ejaculate (oligozoospermia) and dilatations of the epididymal head but normal sperm motility, similar to DNAH5 deficient mice. The findings of this translational study demonstrate, in both mice and men, that efferent duct ciliary motility is important for male reproductive fitness and uncovers a novel pathomechanism distinct from primary defects of sperm motility (asthenozoospermia). If future work can identify environmental factors or defects in genes other than DNAH5 that cause efferent duct cilia dysmotility, this will help unravel other causes of oligozoospermia and may influence future practices in genetic and fertility counseling as well as ART.

Defects in the cytoplasmic assembly of axonemal dynein arms cause morphological abnormalities and dysmotility in sperm cells leading to male infertility

Axonemal protein complexes, such as outer (ODA) and inner (IDA) dynein arms, are responsible for the generation and regulation of flagellar and ciliary beating. Studies in various ciliated model organisms have shown that axonemal dynein arms are first assembled in the cell cytoplasm and then delivered into axonemes during ciliogenesis. In humans, mutations in genes encoding for factors involved in this process cause structural and functional defects of motile cilia in various organs such as the airways and result in the hereditary disorder primary ciliary dyskinesia (PCD). Despite extensive knowledge about the cytoplasmic assembly of axonemal dynein arms in respiratory cilia, this process is still poorly understood in sperm flagella. To better define its clinical relevance on sperm structure and function, and thus male fertility, further investigations are required. Here we report the fertility status in different axonemal dynein preassembly mutant males (DNAAF2/ KTU, DNAAF4/ DYX1C1, DNAAF6/ PIH1D3, DNAAF7/ZMYND10, CFAP300/C11orf70 and LRRC6). Besides andrological examinations, we functionally and structurally analyzed sperm flagella of affected individuals by high-speed video- and transmission electron microscopy as well as systematically compared the composition of dynein arms in sperm flagella and respiratory cilia by immunofluorescence microscopy. Furthermore, we analyzed the flagellar length in dynein preassembly mutant sperm. We found that the process of axonemal dynein preassembly is also critical in sperm, by identifying defects of ODAs and IDAs in dysmotile sperm of these individuals. Interestingly, these mutant sperm consistently show a complete loss of ODAs, while some respiratory cilia from the same individual can retain ODAs in the proximal ciliary compartment. This agrees with reports of solely one distinct ODA type in sperm, compared to two different ODA types in proximal and distal respiratory ciliary axonemes. Consistent with observations in model organisms, we also determined a significant reduction of sperm flagellar length in these individuals. These findings are relevant to subsequent studies on the function and composition of sperm flagella in PCD patients and non-syndromic infertile males. Our study contributes to a better understanding of the fertility status in PCD-affected males and should help guide genetic and andrological counselling for affected males and their families.

Impaired male fertility is a major issue and affects several men worldwide. Patients may present with reduced number or complete absence of sperm in the ejaculate, as well as functional and/or morphological sperm defects compromising sperm motility. Despite several diagnostic efforts, the underlying causes of these defects often remain unknown („idiopathic“). The beating of sperm flagella as well as motile cilia, such as those of the respiratory tract, is driven by dynein-based motor protein complexes, namely outer and inner dynein arms. In motile cilia these protein complexes are known to be first assembled in the cytoplasm and then delivered into the cilium. In sperm, this process is still poorly understood. Here we analyze sperm cells of male individuals with mutations in distinct genes encoding factors involved in the preassembly of these motor protein complexes. Consistent with defects in their respiratory ciliated cells, these individuals also demonstrate defects in sperm flagella that cause male infertility due to immotile sperm, with a reduction of flagellar length. Our results strengthen the assumption that the preassembly process of outer and inner dynein arms is clinically relevant also in sperm and provide knowledge that should guide genetic and andrological counselling for a subgroup of men with idiopathic infertility.

Motile cilia and airway disease

A finely regulated system of airway epithelial development governs the differentiation of motile ciliated cells of the human respiratory tract, conferring the body's mucociliary clearance defence system. Human cilia dysfunction can arise through genetic mutations and this is a cause of debilitating disease morbidities that confer a greatly reduced quality of life. The inherited human motile ciliopathy disorder, primary ciliary dyskinesia (PCD), can arise from mutations in genes affecting various aspects of motile cilia structure and function through deficient production, transport and assembly of cilia motility components or through defective multiciliogenesis. Our understanding about the development of the respiratory epithelium, motile cilia biology and the implications for human pathology has expanded greatly over the past 20 years since isolation of the first PCD gene, rising to now nearly 50 genes. Systems level insights about cilia motility in health and disease have been made possible through intensive molecular and omics (genomics, transcriptomics, proteomics) research, applied in ciliate organisms and in animal and human disease modelling. Here, we review ciliated airway development and the genetic stratification that underlies PCD, for which the underlying genotype can increasingly be connected to biological mechanism and disease prognostics. Progress in this field can facilitate clinical translation of research advances, with potential for great medical impact, e.g. through improvements in ciliopathy disease diagnosis, management, family counselling and by enhancing the potential for future genetically tailored approaches to disease therapeutics.

Genetic underpinnings of asthenozoospermia

Asthenozoospermia (AZS), defined by reduced motility or absent sperm motility, is one of the main causes of male infertility. This condition may be divided into isolated AZS in the absence of other symptoms and syndromic AZS, which is characterized by several concurrent clinical symptoms. Sperm motility depends on fully functional flagellum, energy availability, and the crosstalk of several signaling pathways; therefore, mutations in genes involved in flagellar assembly and motile regulation can cause AZS. Thus, it is crucial to understand the genetic causes and mechanisms contributing to AZS. In this review, we summarize the current knowledge about the particular genes and mechanisms involved in intact flagellum, energy availability, and signaling transduction that could cause human AZS and discuss the respective gene defects known to be responsible for these abnormalities. Additionally, we discuss intracytoplasmic sperm injection outcomes and offspring health where available in these cases.

Immunofluorescence Analysis as a Diagnostic Tool in a Spanish Cohort of Patients with Suspected Primary Ciliary Dyskinesia

Primary ciliary dyskinesia (PCD) is an autosomal recessive rare disease caused by an alteration of ciliary structure. Immunofluorescence, consisting in the detection of the presence and distribution of cilia proteins in human respiratory cells by fluorescence, has been recently proposed as a technique to improve understanding of disease-causing genes and diagnosis rate in PCD. The objective of this study is to determine the accuracy of a panel of four fluorescently labeled antibodies (DNAH5, DNALI1, GAS8 and RSPH4A or RSPH9) as a PCD diagnostic tool in the absence of transmission electron microscopy analysis. The panel was tested in nasal brushing samples of 74 patients with clinical suspicion of PCD. Sixty-eight (91.9%) patients were evaluable for all tested antibodies. Thirty-three cases (44.6%) presented an absence or mislocation of protein in the ciliary axoneme (15 absent and 3 proximal distribution of DNAH5 in the ciliary axoneme, 3 absent DNAH5 and DNALI1, 7 absent DNALI1 and cytoplasmatic localization of GAS8, 1 absent GAS8, 3 absent RSPH9 and 1 absent RSPH4A). Fifteen patients had confirmed or highly likely PCD but normal immunofluorescence results (68.8% sensitivity and 100% specificity). In conclusion, immunofluorescence analysis is a quick, available, low-cost and reliable diagnostic test for PCD, although it cannot be used as a standalone test.

Molecular genetics of infertility: loss-of-function mutations in humans and corresponding knockout/mutated mice

BACKGROUND

Infertility is a major issue in human reproductive health, affecting an estimated 15% of couples worldwide. Infertility can result from disorders of sex development (DSD) or from reproductive endocrine disorders (REDs) with onset in infancy, early childhood or adolescence. Male infertility, accounting for roughly half of all infertility cases, generally manifests as decreased sperm count (azoospermia or oligozoospermia), attenuated sperm motility (asthenozoospermia) or a higher proportion of morphologically abnormal sperm (teratozoospermia). Female infertility can be divided into several classical types, including, but not limited to, oocyte maturation arrest, premature ovarian insufficiency (POI), fertilization failure and early embryonic arrest. An estimated one half of infertility cases have a genetic component; however, most genetic causes of human infertility are currently uncharacterized. The advent of high-throughput sequencing technologies has greatly facilitated the identification of infertility-associated gene mutations in patients over the past 20 years.

OBJECTIVE AND RATIONALE

This review aims to conduct a narrative review of the genetic causes of human infertility. Loss-of-function mutation discoveries related to human infertility are summarized and further illustrated in tables. Corresponding knockout/mutated animal models of causative genes for infertility are also introduced.

SEARCH METHODS

A search of the PubMed database was performed to identify relevant studies published in English. The term 'mutation' was combined with a range of search terms related to the core focus of the review: infertility, DSD, REDs, azoospermia or oligozoospermia, asthenozoospermia, multiple morphological abnormalities of the sperm flagella (MMAF), primary ciliary dyskinesia (PCD), acephalic spermatozoa syndrome (ASS), globozoospermia, teratozoospermia, acrosome, oocyte maturation arrest, POI, zona pellucida, fertilization defects and early embryonic arrest.

OUTCOMES

Our search generated ∼2000 records. Overall, 350 articles were included in the final review. For genetic investigation of human infertility, the traditional candidate gene approach is proceeding slowly, whereas high-throughput sequencing technologies in larger cohorts of individuals is identifying an increasing number of causative genes linked to human infertility. This review provides a wide panel of gene mutations in several typical forms of human infertility, including DSD, REDs, male infertility (oligozoospermia, MMAF, PCD, ASS and globozoospermia) and female infertility (oocyte maturation arrest, POI, fertilization failure and early embryonic arrest). The causative genes, their identified mutations, mutation rate, studied population and their corresponding knockout/mutated mice of non-obstructive azoospermia, MMAF, ASS, globozoospermia, oocyte maturation arrest, POI, fertilization failure and early embryonic arrest are further illustrated by tables. In this review, we suggest that (i) our current knowledge of infertility is largely obtained from knockout mouse models; (ii) larger cohorts of clinical cases with distinct clinical characteristics need to be recruited in future studies; (iii) the whole picture of genetic causes of human infertility relies on both the identification of more mutations for distinct types of infertility and the integration of known mutation information; (iv) knockout/mutated animal models are needed to show whether the phenotypes of genetically altered animals are consistent with findings in human infertile patients carrying a deleterious mutation of the homologous gene; and (v) the molecular mechanisms underlying human infertility caused by pathogenic mutations are largely unclear in most current studies.

WILDER IMPLICATIONS

It is important to use our current understanding to identify avenues and priorities for future research in the field of genetic causes of infertility as well as to apply mutation knowledge to risk prediction, genetic diagnosis and potential treatment for human infertility.

Motile ciliopathies

Motile cilia are highly complex hair-like organelles of epithelial cells lining the surface of various organ systems. Genetic mutations (usually with autosomal recessive inheritance) that impair ciliary beating cause a variety of motile ciliopathies, a heterogeneous group of rare disorders. The pathogenetic mechanisms, clinical symptoms and severity of the disease depend on the specific affected genes and the tissues in which they are expressed. Defects in the ependymal cilia can result in hydrocephalus, defects in the cilia in the fallopian tubes or in sperm flagella can cause female and male subfertility, respectively, and malfunctional motile monocilia of the left-right organizer during early embryonic development can lead to laterality defects such as situs inversus and heterotaxy. If mucociliary clearance in the respiratory epithelium is severely impaired, the disorder is referred to as primary ciliary dyskinesia, the most common motile ciliopathy. No single test can confirm a diagnosis of motile ciliopathy, which is based on a combination of tests including nasal nitric oxide measurement, transmission electron microscopy, immunofluorescence and genetic analyses, and high-speed video microscopy. With the exception of azithromycin, there is no evidence-based treatment for primary ciliary dyskinesia; therapies aim at relieving symptoms and reducing the effects of reduced ciliary motility.

Altered Dynein Axonemal Assembly Factor 1 Expression in C-Boutons in Bulbar and Spinal Cord Motor-Neurons in Sporadic Amyotrophic Lateral Sclerosis

Dyneins are major components of microtubules. Dynein assembly is modulated by a heterogeneous group of dynein axonemal assembly factors (DNAAFs). The present study analyzes dynein axonemal assembly factor 1 (DNAAF1) and leucine-rich repeat-containing protein 50 (LRRC50), the corresponding encoded protein, in lower motor neurons in spinal cord of sALS postmortem samples and hSOD1-G93A transgenic mice compared with controls. DNAAF1 mRNA is significantly reduced in the anterior horn in sALS, and LRRC50 immunoreactivity is significantly reduced in C-boutons of the remaining motor neurons of the anterior horn, dorsal nucleus of the vagus nerve, and hypoglossal nuclei at terminal stages of ALS. LRRC50 immunoreactivity has a perinuclear distribution in motor neurons in sALS thus suggesting a disorder of transport. The number of LRRC50-/S1R-immunoreactive structures is also significantly decreased in hSOD1-G93A transgenic mice at the age of 90 days (preclinical stages), and the number of motor neurons with LRRC50-immunoreactive structures is significantly reduced in animals aged 150 days (clinical stages). These observations suggest cholinergic denervation of motor neurons as a pathogenic factor in motor neuron disease. LRRC50 protein levels were not detected in human CSF.

Sperm defects in primary ciliary dyskinesia and related causes of male infertility

The core axoneme structure of both the motile cilium and sperm tail has the same ultrastructural 9 + 2 microtubular arrangement. Thus, it can be expected that genetic defects in motile cilia also have an effect on sperm tail formation. However, recent studies in human patients, animal models and model organisms have indicated that there are differences in components of specific structures within the cilia and sperm tail axonemes. Primary ciliary dyskinesia (PCD) is a genetic disease with symptoms caused by malfunction of motile cilia such as chronic nasal discharge, ear, nose and chest infections and pulmonary disease (bronchiectasis). Half of the patients also have situs inversus and in many cases male infertility has been reported. PCD genes have a role in motile cilia biogenesis, structure and function. To date mutations in over 40 genes have been identified cause PCD, but the exact effect of these mutations on spermatogenesis is poorly understood. Furthermore, mutations in several additional axonemal genes have recently been identified to cause a sperm-specific phenotype, termed multiple morphological abnormalities of the sperm flagella (MMAF). In this review, we discuss the association of PCD genes and other axonemal genes with male infertility, drawing particular attention to possible differences between their functions in motile cilia and sperm tails.

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

CFAP300: Mutations in Slavic Patients with Primary Ciliary Dyskinesia and a Role in Ciliary Dynein Arms Trafficking

Primary ciliary dyskinesia (PCD) is a rare, genetically heterogeneous hereditary disease from a class of ciliopathies. In spite of the recent progress, the genetic basis of PCD in one-third of patients remains unknown. In search for new genes and/or mutations, whole-exome sequencing was performed in 120 unrelated Polish patients with PCD, in whom no genetic cause of PCD was earlier identified. Among a number of pathogenic variants in PCD genes, mutations in CFAP300 (alias C11orf70) were detected. Extended screening in the whole Polish PCD cohort revealed the relatively high frequency (3.6%) of otherwise rare c.[198_200 del_insCC] variant, indicating that it should be included in population-specific genetic tests for PCD in Slavic populations. Immunofluorescence analysis of the respiratory epithelial cells from patients with CFAP300 mutations revealed the absence or aberrant localization of outer and inner dynein arm markers, consistent with transmission electron microscope images indicating the lack of both dynein arms. Interestingly, the disparate localization of DNAH5 and DNALI1 proteins in patients with CFAP300 mutations suggested differential mechanisms for the trafficking of preassembled outer and inner dynein arms to the axoneme. The profile of CFAP300 expression during ciliogenesis in suspension culture was consistent with its role in cilia assembly. Gene silencing experiments, performed in a model organism, Schmidtea mediterranea (flatworm), pointed to the conserved role of CFAP300 in ciliary function.

Implementation of a Gene Panel for Genetic Diagnosis of Primary Ciliary Dyskinesia

INTRODUCTION

Primary ciliary dyskinesia (PCD) is characterized by an alteration in the ciliary structure causing difficulty in the clearance of respiratory secretions. Diagnosis is complex and based on a combination of techniques. The objective of this study was to design a gene panel including all known causative genes, and to corroborate their diagnostic utility in a cohort of Spanish patients.

METHODS

This was a multicenter cross-sectional study of patients with a high suspicion of PCD, according to European Respiratory Society criteria, designed around a gene panel for massive sequencing using SeqCap EZ capture technology that included 44 genes associated with PCD.

RESULTS

We included 79 patients, 53 of whom had a diagnosis of confirmed or highly probable PCD. The sensitivity of the gene panel was 81.1%, with a specificity of 100%. Candidate variants were found in some of the genes of the panel in 43 patients with PCD, 51.2% (22/43) of whom were homozygotes and 48.8% (21/43) compound heterozygotes. The most common causative genes were DNAH5 and CCDC39. We found 52 different variants, 36 of which were not previously described in the literature.

CONCLUSIONS

The design and implementation of a tailored gene panel produces a high yield in the genetic diagnosis of PCD. This panel provides a better understanding of the causative factors involved in these patients and lays down the groundwork for future therapeutic approaches.

Novel DNAAF6 variants identified by whole-exome sequencing cause male infertility and primary ciliary dyskinesia

PURPOSE

To identify the genetic cause of patients with primary ciliary dyskinesia (PCD) and male infertility from two unrelated Han Chinese families.

METHODS

We conducted whole-exome sequencing of three individuals with PCD and male infertility from two unrelated Chinese families, and performed a targeted look-up for DNAAF6 variants in our previously reported cohort of 442 individuals (219 with isolated oligoasthenospermia and 223 fertile controls). Ultrastructural and immunostaining analyses of patients' spermatozoa were performed. The pathogenicity of the variants was validated using patient's spermatozoa and HEK293T cells. Intracytoplasmic sperm injection (ICSI) treatment was conducted in two patients.

RESULTS

We identified one novel hemizygous frameshift variant (NM_173494, c.319_329del: p.R107fs) of DNAAF6 gene (previously named PIH1D3) in family 1 and one novel hemizygous missense variant (c.290G>T: p.G97V) in family 2. No hemizygous deleterious variants in DNAAF6 were detected in the control cohort of 442 individuals. Ultrastructural and immunostaining analyses of patients' spermatozoa showed the absence of outer and inner dynein arms in sperm flagella. Both variants were proven to lead to DNAAF6 protein degradation in HEK293T cells. Both patients carrying DNAAF6 variants underwent one ICSI cycle and delivered one healthy child each.

CONCLUSION

We identified novel DNAAF6 variants causing male infertility and PCD in Han Chinese patients. This finding extended the spectrum of variants in DNAAF6 and revealed new light on the impact of DNAAF6 variants in sperm flagella.

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.

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.

Role of the Novel Hsp90 Co-Chaperones in Dynein Arms' Preassembly

The outer and inner dynein arms (ODAs and IDAs) are composed of multiple subunits including dynein heavy chains possessing a motor domain. These complex structures are preassembled in the cytoplasm before being transported to the cilia. The molecular mechanism(s) controlling dynein arms’ preassembly is poorly understood. Recent evidence suggests that canonical R2TP complex, an Hsp-90 co-chaperone, in cooperation with dynein axonemal assembly factors (DNAAFs), plays a crucial role in the preassembly of ODAs and IDAs. Here, we have summarized recent data concerning the identification of novel chaperone complexes and their role in dynein arms’ preassembly and their association with primary cilia dyskinesia (PCD), a human genetic disorder.

Ciliary Proteins: Filling the Gaps. Recent Advances in Deciphering the Protein Composition of Motile Ciliary Complexes

Cilia are highly evolutionarily conserved, microtubule-based cell protrusions present in eukaryotic organisms from protists to humans, with the exception of fungi and higher plants. Cilia can be broadly divided into non-motile sensory cilia, called primary cilia, and motile cilia, which are locomotory organelles. The skeleton (axoneme) of primary cilia is formed by nine outer doublet microtubules distributed on the cilium circumference. In contrast, the skeleton of motile cilia is more complex: in addition to outer doublets, it is composed of two central microtubules and several diverse multi-protein complexes that are distributed periodically along both types of microtubules. For many years, researchers have endeavored to fully characterize the protein composition of ciliary macro-complexes and the molecular basis of signal transduction between these complexes. Genetic and biochemical analyses have suggested that several hundreds of proteins could be involved in the assembly and function of motile cilia. Within the last several years, the combined efforts of researchers using cryo-electron tomography, genetic and biochemical approaches, and diverse model organisms have significantly advanced our knowledge of the ciliary structure and protein composition. Here, we summarize the recent progress in the identification of the subunits of ciliary complexes, their precise intraciliary localization determined by cryo-electron tomography data, and the role of newly identified proteins in cilia.

Induced Pluripotent Stem Cells for Primary Ciliary Dyskinesia Modeling and Personalized Medicine

Primary ciliary dyskinesia (PCD) is a rare and heterogeneous genetic disorder that affects the structure and function of motile cilia. In the airway epithelium, impaired ciliary motion results in reduced or absent mucociliary clearance that leads to the appearance of chronic airway infection, sinusitis, and bronchiectasis. Currently, there is no effective treatment for PCD, and research is limited by the lack of convenient models to study this disease and investigate innovative therapies. Furthermore, the high heterogeneity of PCD genotypes is likely to hinder the development of a single therapy for all patients. The generation of patient-derived, induced pluripotent stem cells, and their differentiation into airway epithelium, as well as genome editing technologies, could represent major tools for in vitro PCD modeling and for developing personalized therapies. Here, we review PCD pathogenesis and then discuss how human induced pluripotent stem cells could be used to model this disease for the development of innovative, patient-specific biotherapies.

Lack of GAS2L2 Causes PCD by Impairing Cilia Orientation and Mucociliary Clearance

Primary ciliary dyskinesia (PCD) is a genetic disorder in which impaired ciliary function leads to chronic airway disease. Exome sequencing of a PCD subject identified an apparent homozygous frameshift variant, c.887_890delTAAG (p.Val296Glyfs^∗13), in exon 5; this frameshift introduces a stop codon in amino acid 308 of the growth arrest-specific protein 2-like 2 (GAS2L2). Further genetic screening of unrelated PCD subjects identified a second proband with a compound heterozygous variant carrying the identical frameshift variant and a large deletion (c.867_^∗343+1207del; p.?) starting in exon 5. Both individuals had clinical features of PCD but normal ciliary axoneme structure. In this research, using human nasal cells, mouse models, and X.laevis embryos, we show that GAS2L2 is abundant at the apical surface of ciliated cells, where it localizes with basal bodies, basal feet, rootlets, and actin filaments. Cultured GAS2L2-deficient nasal epithelial cells from one of the affected individuals showed defects in ciliary orientation and had an asynchronous and hyperkinetic (GAS2L2-deficient = 19.8 Hz versus control = 15.8 Hz) ciliary-beat pattern. These results were recapitulated in Gas2l2^-/- mouse tracheal epithelial cell (mTEC) cultures and in X. laevis embryos treated with Gas2l2 morpholinos. In mice, the absence of Gas2l2 caused neonatal death, and the conditional deletion of Gas2l2 impaired mucociliary clearance (MCC) and led to mucus accumulation. These results show that a pathogenic variant in GAS2L2 causes a genetic defect in ciliary orientation and impairs MCC and results in PCD.

The Swiss Primary Ciliary Dyskinesia registry: objectives, methods and first results

Primary ciliary dyskinesia (PCD) is a rare, hereditary, multiorgan disease caused by defects in the structure and function of motile cilia. It results in a wide range of clinical manifestations, most commonly in the upper and lower airways. Central data collection in national and international registries is essential to studying the epidemiology of rare diseases and filling in gaps in knowledge of diseases such as PCD. For this reason, the Swiss Primary Ciliary Dyskinesia Registry (CH-PCD) was founded in 2013 as a collaborative project between epidemiologists and adult and paediatric pulmonologists. We describe the objectives and methodology of the CH-PCD, present initial results, and give an overview of current and ongoing projects. The registry records patients of any age, suffering from PCD, who are treated and resident in Switzerland. It collects information from patients identified through physicians, diagnostic facilities and patient organisations. The registry dataset contains data on diagnostic evaluations, lung function, microbiology and imaging, symptoms, treatments and hospitalisations. By May 2018, CH-PCD has contacted 566 physicians of different specialties and identified 134 patients with PCD. At present, this number represents an overall 1 in 63,000 prevalence of people diagnosed with PCD in Switzerland. Prevalence differs by age and region; it is highest in children and adults younger than 30 years, and in Espace Mittelland. The median age of patients in the registry is 25 years (range 5–73), and 41 patients have a definite PCD diagnosis based on recent international guidelines. Data from CH-PCD are contributed to international collaborative studies and the registry facilitates patient identification for nested studies. CH-PCD has proven to be a valuable research tool that already has highlighted weaknesses in PCD clinical practice in Switzerland. Trial registration number NCT03606200

Recessive DNAH9 Loss-of-Function Mutations Cause Laterality Defects and Subtle Respiratory Ciliary-Beating Defects

Dysfunction of motile monocilia, altering the leftward flow at the embryonic node essential for determination of left-right body asymmetry, is a major cause of laterality defects. Laterality defects are also often associated with reduced mucociliary clearance caused by defective multiple motile cilia of the airway and are responsible for destructive airway disease. Outer dynein arms (ODAs) are essential for ciliary beat generation, and human respiratory cilia contain different ODA heavy chains (HCs): the panaxonemally distributed γ-HC DNAH5, proximally located β-HC DNAH11 (defining ODA type 1), and the distally localized β-HC DNAH9 (defining ODA type 2). Here we report loss-of-function mutations in DNAH9 in five independent families causing situs abnormalities associated with subtle respiratory ciliary dysfunction. Consistent with the observed subtle respiratory phenotype, high-speed video microscopy demonstrates distally impaired ciliary bending in DNAH9 mutant respiratory cilia. DNAH9-deficient cilia also lack other ODA components such as DNAH5, DNAI1, and DNAI2 from the distal axonemal compartment, demonstrating an essential role of DNAH9 for distal axonemal assembly of ODAs type 2. Yeast two-hybrid and co-immunoprecipitation analyses indicate interaction of DNAH9 with the ODA components DNAH5 and DNAI2 as well as the ODA-docking complex component CCDC114. We further show that during ciliogenesis of respiratory cilia, first proximally located DNAH11 and then distally located DNAH9 is assembled in the axoneme. We propose that the β-HC paralogs DNAH9 and DNAH11 achieved specific functional roles for the distinct axonemal compartments during evolution with human DNAH9 function matching that of ancient β-HCs such as that of the unicellular Chlamydomonas reinhardtii.