Genetic diagnosis of motile ciliopathies is conducted by healthcare, commercial and private laboratories. 88 genes have been implicated in motile ciliopathies (PCD, male infertility and associated disorders). Gene-disease relationships are uncertain where evidence is limited, risking inaccurate reporting and diagnosis. The ClinGen Motile Ciliopathy Gene Curation Expert Panel (GCEP) was set up collaboratively with BEAT-PCD ERS CRC in 2021. The GCEP comprises geneticists, pulmonologists and biocurators (Canada, France, Germany, Norway, Poland, Spain, Tunisia, UK, USA) tasked with classifying clinical validity of gene-disease relationships in motile ciliopathies to aid interpretation of genetic results. As an early step, the GCEP drew up guidelines to capture the critical details of motile ciliopathy cases and to score genetic and experimental evidence conservatively and consistently. The GCEP meets monthly and so far has curated 33 gene-disease relationships (https://clinicalgenome.org/affiliation/40102/). 22 curations have reached a definitive classification as the role of the gene in disease has been repeatedly demonstrated and upheld over time, 4 were disputed. These efforts provide a basis for future classifications of gene-disease relationships. The goal of the GCEP is to leverage emerging research to enhance the reliability of genetic testing for improved clinical detection and diagnosis of motile ciliopathies.
PCD can be diagnosed by bi-allelic pathogenic mutations in one of >50 ciliary genes. ~ 60% of patients with an identified genetic cause have private mutations not previously reported in another patient. Increasing numbers of variants of unknown significance (VUS, i.e. unknown if they are pathogenic) are identified. As clinical genetic testing is increasingly used for PCD, there is a need to develop a public access resource to identify if variants have previously been reported to be associated with disease. Our aim was to establish an online open database registering gene mutations and specific combinations of variants causing PCD. A panel of clinicians and geneticists with expertise in PCD identified database fields to link each variant with the associated diagnostic, clinical and genetic evidence supporting pathogenicity. A literature search was conducted to identify published mutations causing PCD. Database curators checked mutation nomenclature and classification of variants was carried out following ACMG guidelines. 624 papers were identified. Following abstract review 235 papers yielded 1,282 PCD patients. Additionally, 201 PCD cases from a diagnostic centre were entered to pilot the database. 1214 mutations were included in CiliaVar. The majority of mutations (52%) were in 4 genes DNAH5, DNAH11, CCDC39, CCDC40. The most common variants reported are CCDC40: c.248del (n=41 patients) and DNAI1: c.48+2dupT (n=49). 21% of the distinct variants are classified as VUS. The online open database CiliaVar will improve access to PCD variant information to improve the diagnosis of PCD. Acknowledgments: BEAT-PCD ERS clinical research collobaration
Primary ciliary dyskinesia (PCD) is a genetically heterogeneous disease of motile cilia. Even though PCD is widely studied, North-African patients have been rarely explored. In this study, we aim at confirming the clinical diagnosis and explore the genetic spectrum of PCD in a cohort of Tunisian patients. Forty clinically diagnosed patients with PCD belonging to 34 families were recruited from Tunisian pediatric departments. In each proband, targeted capture PCD panel sequencing of the 40 PCD genes was performed. PCD panel sequencing identified bi-allelic mutations in 82% of the families in eight PCD genes. Remarkably, 23.5% of patients carried the same c.2190del CCDC39 mutation. Single nucleotide polymorphism profiling in six unrelated patients carrying this mutation has revealed a founder effect in North-African patients. This mutation is estimated to date back at least 1,400-1,750 years ago. The identification of this major allele allowed us to suggest a cost-effective genetic diagnostic strategy in North-African patients with PCD.
Primary ciliary dyskinesia (PCD) is a rare autosomal-recessive disorder characterized by abnormal motile ciliary function. Because motile cilia and sperm flagella share common axonemal structures, male individuals are supposed to be infertile and female may have hypofertility. We hypothesize that a correlation may exist between the risk of hypofertility and the genotype in PCD. We retrospectively recorded the fertility status of adult patients with a definite PCD diagnosis, based on ultrastructural phenotype and an established genotype based on the identification of two non-ambiguous mutations in a known PCD gene. Fertility was considered as normal in case of a spontaneous pregnancy. Hypofertility was defined when attempts for spontaneous conception were unsuccessful for at least one year and/or pregnancy was obtained after assisted reproductive technologies. Data on fertility were available for 83 (50 %) patients. Among the 34 included females, 14 (35.8%) had been spontaneously pregnant and among the 49 male patients, 10 (20.4%) had spontaneously fathered a child. When looking at the different genes involved, in groups containing at least 3 patients, we observed that patients with mutations in CCDC39 or CCDC40 (associated with inner dynein arms with microtubular disorganization defects) and those with mutations in DNAAF1 (LRRC50), or LRRC6 (associated with absence of outer and inner dynein arms) were more likely to be hypofertile (chi-squared test 17.5, p=0.004) and whereas those with RSPH4A mutations (associated with abnormal central complex) are more likely to be fertile. Hypofertility is not always observed in PCD and is dependent of gene defect.
Primary ciliary dyskinesia (PCD) is a rare autosomal recessive disorder (prevalence 1:10 000 to 1:40 000 births) characterised by impaired mucociliary clearance because of abnormal motile ciliary function [1, 2]. Five main ultrastructural PCD phenotypes have been described. Most result from a lack of dynein arms (DAs): no outer and inner DAs (2DAs), outer DAs alone (ODA) or inner DAs with microtubular disorganisation (IDA/MTD); or defects yielding an abnormal central complex (CC). Some patients with genetically confirmed PCD have apparently normal ciliary structure on electron microscopy (nEM). More than 30 genes encoding proteins involved in the structure or assembly of the axoneme, the ciliary internal cytoskeleton, are implicated in PCD [3]; their analysis enables identification of bi-allelic disease-causing mutations in 50–75% of patients. Approximately half of PCD cases are associated with situs inversus , thereby defining Kartagener's syndrome. Moreover, because motile cilia and sperm flagella share common axonemal structures, most PCD-affected males are thought to be infertile [4]. According to the literature, male infertility is caused by severe or total asthenozoospermia and is currently treated by recourse to in vitro fertilisation or intracytoplasmic sperm injection [5, 6]. However, spontaneous fatherhood of PCD patients has been reported. Infertility, observed in 75% of male and 61% of female PCD patients, is dependent on ultrastructural and gene defects We thank all the individuals and their families for their cooperation, as well as all the referring physicians. The researchers participate in the network of COST Action BEAT-PCD (Better Evidence to Advance Therapeutic Options for PCD; no. BM 1407). L. Bassinet, I. Honoré, J.-.F Papon, A. Coste, E. Escudier, S. Amselem, B. Maitre, M. Legendre and S. Christin-Maitre are members of the RadiCONetwork (Inserm, France).
Rationale: Although children with primary ciliary dyskinesia (PCD) typically have low nasal nitric oxide (nNO), some children with indisputable PCD may have unexplained high nNO concentrations. Objectives: To look for relationships between nNO measures and genetic findings (and cilia motility or ultrastructure when available) in children with PCD with known genotypes. Methods: We retrospectively studied 73 children with PCD (median age, 9.5 [range, 2.1-18.2] yr). nNO was the mean value of a plateau reached while the velum was closed (nNO-VC; threshold, 77 nl ⋅ min-1) or was calculated as the average of five peaks obtained during tidal breathing (threshold, 40 nl ⋅ min-1). Ciliary beat was classified as either motile (including dyskinetic pattern) or immotile, depending on whether motility was present or absent in all cilia, or as a mixture of motile and immotile cilia. Genotypes were classified as pathogenic mutations in genes known to be associated with high nNO (mild genotype), biallelic truncating mutations in other genes (severe mutations), or putative hypomorphic pathogenic mutations (missense, single amino acid deletion, or moderate splicing mutations) in at least one allele believed to be possibly associated with residual production of a functional protein. Results: nNO was above the discriminant threshold in 16 of 73 (21.9%) children (11 nNO-VC and 5 nNO during tidal breathing). High nNO was less frequent in children with severe mutations (2 of 42) than in those with mild genotypes (7 of 10) or at least one hypomorphic mutation (7 of 21) (P < 0.0001). Median (interquartile range) nNO-VC values (n = 60) were significantly different in the three genotype groups: severe mutations, 18 (10-26) nl ⋅ min-1 (n = 36); possible residual functional protein production (putative hypomorphic mutations), 23 (16-68) nl ⋅ min-1 (n = 17); and mild genotypes, 139 (57-216) nl ⋅ min-1 (n = 7) (P = 0.0002). The higher the cilia motility, the higher the nNO-VC (16 [10-23], 23 [17-56], and 78 [45-93] nl ⋅ min-1 in patients with immotile, dyskinetic motile and immotile, and dyskinetic motile cilia, respectively; P < 0.0001), while nNO values were scattered across different ultrastructure defects (P = 0.07). Conclusions: In children with PCD, high nNO values were linked not only to specific genes but also to potentially hypomorphic mutations in other genes (with possible functional protein production). nNO values increased with the proportion of motile cilia.
