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.

Primary Ciliary Dyskinesia Associated Disease-Causing Variants in CCDC39 and CCDC40 Cause Axonemal Absence of Inner Dynein Arm Heavy Chains DNAH1, DNAH6, and DNAH7.

Disease-causing bi-allelic DNA variants in CCDC39 and CCDC40 are frequent causes of the hereditary disorder of primary ciliary dyskinesia (PCD). The encoded proteins form a molecular ruler complex, crucial for maintaining the 96 nm repeat units along the ciliary axonemes. Defects of those proteins cause a stiff, rapid, and flickery ciliary beating pattern, recurrent respiratory infections, axonemal disorganization, and abnormal assembly of GAS8, CCDC39, and DNALI1. We performed molecular characterization of the defects in the 96 nm axonemal ruler due to disease-causing variants in CCDC39 and CCDC40 and analyzed the effect on additional axonemal components. We identified a cohort of 51 individuals with disease-causing variants in CCDC39 and CCDC40 via next-generation sequencing techniques and demonstrated that the IDA heavy chains DNAH1, DNAH6, and DNAH7 are conspicuously absent within the respiratory ciliary axonemes by immunofluorescence analyses. Hence, we show for the first time that the centrin2 (CETN2) containing IDAs are also affected. These findings underscore the crucial role of CCDC39 and CCDC40 in the assembly and function of IDAs in human respiratory cilia. Thus, our data improve the diagnostics of axonemal ruler defects by further characterizing the associated molecular IDA defects.

A novel splicing mutation DNAH5 c.13,338 + 5G > C is involved in the pathogenesis of primary ciliary dyskinesia in a family with primary familial brain calcification.

BACKGROUND: Primary ciliary dyskinesia (PCD) is an autosomal recessive hereditary disease characterized by recurrent respiratory infections. In clinical manifestations, DNAH5 (NM_001361.3) is one of the recessive pathogenic genes. Primary familial brain calcification (PFBC) is a neurodegenerative disease characterized by bilateral calcification in the basal ganglia and other brain regions. PFBC can be inherited in an autosomal dominant or recessive manner. A family with PCD caused by a DNAH5 compound heterozygous variant and PFBC caused by a MYORG homozygous variant was analyzed. METHODS: In this study, we recruited three generations of Han families with primary ciliary dyskinesia combined with primary familial brain calcification. Their clinical phenotype data were collected, next-generation sequencing was performed to screen suspected pathogenic mutations in the proband and segregation analysis of families was carried out by Sanger sequencing. The mutant and wild-type plasmids were constructed and transfected into HEK293T cells instantaneously, and splicing patterns were detected by Minigene splicing assay. The structure and function of mutations were analyzed by bioinformatics analysis. RESULTS: The clinical phenotypes of the proband (II10) and his sister (II8) were bronchiectasis, recurrent pulmonary infection, multiple symmetric calcifications of bilateral globus pallidus and cerebellar dentate nucleus, paranasal sinusitis in the whole group, and electron microscopy of bronchial mucosa showed that the ciliary axoneme was defective. There was also total visceral inversion in II10 but not in II8. A novel splice variant C.13,338 + 5G > C and a frameshift variant C.4314delT (p. Asn1438lysfs *10) were found in the DNAH5 gene in proband (II10) and II8. c.347_348dupCTGGCCTTCCGC homozygous insertion variation was found in the MYORG of the proband. The two pathogenic genes were co-segregated in the family. Minigene showed that DNAH5 c.13,338 + 5G > C has two abnormal splicing modes: One is that part of the intron bases where the mutation site located is translated, resulting in early translation termination of DNAH5; The other is the mutation resulting in the deletion of exon76. CONCLUSIONS: The newly identified DNAH5 splicing mutation c.13,338 + 5G > C is involved in the pathogenesis of PCD in the family, and forms a compound heterozygote with the pathogenic variant DNAH5 c.4314delT lead to the pathogenesis of PCD.

[Clinical and genetic characteristics of a case of primary ciliary dyskinesia caused by new frameshift mutation of the DNAH5 gene].

OBJECTIVE: To investigate the clinical and genetic characteristics of a case of primary ciliary dyskinesia (PCD). METHODS: We collected the clinical data on a case of PCD treated in the Department of Reproductive Medicine of Linyi People's Hospital in July 2020, detected the genes of the patient by whole-exome sequencing (WES), verified the candidate mutations by Sanger sequencing, and predicted the protein structure of the mutant gene by SWISS-MODEL. RESULTS: The proband was found with the clinical phenotypes of chronic rhinitis, bronchiectasis, visceral transposition and male infertility. WES revealed a homozygous frameshift variation of c.12890dup (p.N4297Kfs*13) in exon 74 of the DNAH5 gene, which led to the premature termination of polypeptide chain synthesis and affected the gene function. SWISS-MODEL prediction showed that some of the amino acid residues were deleted after mutation, resulting in a 3D conformational change of the protein. This variation was not recorded in the ClinVar, gnomAD and OMIM databases and, according to the relevant guidelines of the American College of Genetics and Genomics, was classified as a pathogenic variation (PVS1+PM2_P+PM3_P). CONCLUSION: The homozygous variation of the DNAH5 gene c.12890dup (p.N4297Kfs*13) may be the cause of the clinical phenotype of this case of PCD, and the above findings have enriched the variation spectrum of the DNAH5 gene.

Identification of a Homozygous Mutation of CCDC40 in a Chinese Infertile Man with MMAF and PCD-like Phenotypes.

Aims: Asthenozoospermia is the most common factor of male infertility, mainly caused by multiple morphological abnormalities of the sperm flagella (MMAF) and primary ciliary dyskinesia (PCD). Previous studies have shown that genetic factors may contribute to MMAF and PCD. The study aimed to identify novel potentially pathogenic gene mutations in a Chinese infertile man with MMAF and PCD-like phenotypes. Methods: A Chinese infertile man with MMAF and PCD was enrolled in this study. Whole exome sequencing and Sanger sequencing were performed to identify potential causative genes and mutations. Results: A novel homozygous missense mutation (c.1450G>A; p.E484K) of CCDC40 was finally identified and Sanger sequencing confirmed that the patient carried the homozygous mutation, which was inherited from his parents. We reported the first homozygous missense CCDC40 mutation in infertile men with MMAF but had other milder PCD symptoms. Conclusion: Our findings not only broaden the disease-causing mutation spectrum of CCDC40 but also provide new insight into the correlation between CCDC40 mutations and MMAF.

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.

Primary Ciliary Dyskinesia.

Primary ciliary dyskinesia (PCD) is a rare, genetic disease characterized by dysfunctional motile cilia and abnormal mucociliary clearance, resulting in chronic sino-oto-pulmonary disease, neonatal respiratory distress, subfertility, and organ laterality defects. Over the past 2 decades, research and international collaborations have led to an improved understanding of disease prevalence, classic and variable phenotypes, novel diagnostics, genotype-phenotype correlations, long term morbidity, and innovative therapeutics. However, PCD is often underrecognized in clinical settings and the recent analyses of genetic databases suggest that only a fraction of these patients are being accurately diagnosed. Knowledge of significant advancements, from pathophysiology to the expanded range of clinical manifestations, will have important clinical impacts. These may include increasing disease recognition, improving diagnostic testing and management, and establishing an adequate pool of affected patients to enroll in upcoming clinical therapeutic trials. The objective of this state-of-the-art review is for readers to gain a greater understanding of the clinical spectrum of motile ciliopathies, cutting-edge diagnostic practices, emerging genotype-phenotype associations, and currently accepted management of people with PCD.

Novel SPEF2 variants cause male infertility and likely primary ciliary dyskinesia.

PURPOSE: This study aimed to identify the genetic causes of male infertility and primary ciliary dyskinesia (PCD)/PCD-like phenotypes in three unrelated Han Chinese families. METHODS: We conducted whole-exome sequencing of three patients with male infertility and PCD/PCD-like phenotypes from three unrelated Chinese families. Ultrastructural and immunostaining analyses of patient spermatozoa and respiratory cilia and in vitro analyses were performed to analyze the effects of SPEF2 variants. Intracytoplasmic sperm injection (ICSI) was administered to three affected patients. RESULTS: We identified four novel SPEF2 variants, including one novel homozygous splicing site variant [NC_000005.10(NM_024867.4): c.4447 + 1G > A] of the SPEF2 gene in family 1, novel compound heterozygous nonsense variants [NC_000005.10(NM_024867.4): c.1339C > T (p.R447*) and NC_000005.10(NM_024867.4): c.1645G > T (p.E549*)] in family 2, and one novel homozygous missense variant [NC_000005.10(NM_024867.4): c.2524G > A (p.D842N)] in family 3. All the patients presented with male infertility and PCD/likely PCD. All variants were present at very low levels in public databases, predicted to be deleterious in silico prediction tools, and were further confirmed deleterious by in vitro analyses. Ultrastructural analyses of the spermatozoa of the patients revealed the absence of the central pair complex in the sperm flagella. Immunostaining of the spermatozoa and respiratory cilia of the patients validated the pathogenicity of the SPEF2 variants. All patients carrying SPEF2 variants underwent one ICSI cycle and delivered healthy infants. CONCLUSION: Our study reported four novel pathogenic variants of SPEF2 in three male patients with infertility and PCD/PCD-like phenotypes, which not only extend the spectrum of SPEF2 mutations but also provide information for genetic counseling and treatment of such conditions.

Ciliopathy patient variants reveal organelle-specific functions for TUBB4B in axonemal microtubules.

Tubulin, one of the most abundant cytoskeletal building blocks, has numerous isotypes in metazoans encoded by different conserved genes. Whether these distinct isotypes form cell type- and context-specific microtubule structures is poorly understood. Based on a cohort of 12 patients with primary ciliary dyskinesia as well as mouse mutants, we identified and characterized variants in the TUBB4B isotype that specifically perturbed centriole and cilium biogenesis. Distinct TUBB4B variants differentially affected microtubule dynamics and cilia formation in a dominant-negative manner. Structure-function studies revealed that different TUBB4B variants disrupted distinct tubulin interfaces, thereby enabling stratification of patients into three classes of ciliopathic diseases. These findings show that specific tubulin isotypes have distinct and nonredundant subcellular functions and establish a link between tubulinopathies and ciliopathies.

Neurosurgical intervention for the Meckel-Gruber Syndrome: A systematic review.

INTRODUCTION: Meckel-Gruber Syndrome (MKS) is an autosomal recessive genetic disorder, notable for its triad of occipital encephalocele, polycystic renal dysplasia, and postaxial polydactyly. Identified by Johann Friederich Meckel in 1822, MKS is categorized as a ciliopathy due to gene mutations. Diagnosis is confirmed by the presence of at least two key features. The condition is incompatible with life, leading to death in the womb or shortly after birth. Recent studies have largely focused on the genetic aspects of MKS, with limited information regarding the impact of neurosurgical approaches, particularly in treating encephaloceles. METHODS: A systematic review was performed according to the PRISMA statement. The PubMed, Embase, and Web of Science databases were consulted for data screening and extraction, which was conducted by two independent reviewers. The search strategy aimed to encompass studies documenting cases of MKS with published reports of encephalocele excisions, and the search strings for all databases were: Meckel-Gruber syndrome OR Meckel Gruber syndrome OR Meckel-gruber OR Meckel Gruber. RESULTS: The study included 10 newborns with MKS associated with occipital encephalocele or meningocele, all of whom underwent surgical repair of the occipital sac. The mean gestational age at birth was 36 (± 2) weeks. The mean of birth weight was 3.14 (± 0.85) kilograms. The average head circumference at birth was 33.82 cm (± 2.17). The mean diameter of the encephalocele/meningocele was 5.91 (± 1.02) cm. Other common central nervous system abnormalities included hydrocephalus, Dandy-Walker malformation, and agenesis of the corpus callosum. 40% required shunting for hydrocephalus. Surgery to remove the occipital sac occurred at a median age of 2.5 days (1.5-6.5). The most common post-surgical complication was the need for mechanical ventilation. The most common cause of death was pneumonia and the median age at death was 6.66 (0.03-18) months. CONCLUSION: Our findings suggest that neurosurgical intervention, especially for managing encephaloceles, may offer some improvement in survival, albeit within a context of generally poor prognosis. However, these results should be interpreted with caution.

Primary Ciliary Dyskinesia and Retinitis Pigmentosa: Novel RPGR Variant and Possible Modifier Gene.

We report a novel RPGR missense variant co-segregated with a familial X-linked retinitis pigmentosa (XLRP) case. The brothers were hemizygous for this variant, but only the proband presented with primary ciliary dyskinesia (PCD). Thus, we aimed to elucidate the role of the RPGR variant and other modifier genes in the phenotypic variability observed in the family and its impact on motile cilia. The pathogenicity of the variant on the RPGR protein was evaluated by in vitro studies transiently transfecting the mutated RPGR gene, and immunofluorescence analysis on nasal brushing samples. Whole-exome sequencing was conducted to identify potential modifier variants. In vitro studies showed that the mutated RPGR protein could not localise to the cilium and impaired cilium formation. Accordingly, RPGR was abnormally distributed in the siblings' nasal brushing samples. In addition, a missense variant in CEP290 was identified. The concurrent RPGR variant influenced ciliary mislocalisation of the protein. We provide a comprehensive characterisation of motile cilia in this XLRP family, with only the proband presenting PCD symptoms. The variant's pathogenicity was confirmed, although it alone does not explain the respiratory symptoms. Finally, the CEP290 gene may be a potential modifier for respiratory symptoms in patients with RPGR mutations.

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

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

[Genetic analysis of a fetus with Meckel syndrome due to variants of TMEM67 gene].

OBJECTIVE: To carry out prenatal diagnosis for a fetus with Meckel syndrome (MKS) and explore its genetic basis. METHODS: A pregnant woman presented at Suzhou Municipal Hospital in February 2018 was selected as the study subject. Clinical data was collected. Muscle tissue sample from the abortus and peripheral blood samples from the couple were collected. Genomic DNA was extracted and subjected to chromosomal microarray analysis (CMA) and whole exome sequencing. Candidate variant was verified by Sanger sequencing. RESULTS: The fetus was found to have microcephaly, oligohydramnios, polycystic kidneys and banana-shaped cerebellum at 18 weeks of gestation. After induction of labor, it was found to have encephalocele, renal cysts and polydactyly. CMA has found no abnormality. Whole exome sequencing revealed novel compound heterozygous variants c.296delA (p.Lys99SerfsTer6) and c.1243G>A (p.Val415Met) in the TMEM67 gene. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), the c.296delA variant was predicted to be pathogenic (PVS1+PM2_Supporting+PP4), whilst the c.1243G>A variant was predicted to be likely pathogenic (PM2_Supporting+PM3+PP3_Moderate+PP4). CONCLUSION: The c.296delA and c.1243G>A compound heterozygous variants of the TMEM67 gene probably underlay the MKS in this fetus.

Stepwise genetic approach for the diagnosis of primary ciliary dyskinesia in highly consanguineous populations.

BACKGROUND: The American Thoracic Society guidelines for the diagnosis of primary ciliary dyskinesia (PCD) consider the presence of a bi-allelic pathogenic variant confirmatory for the diagnosis of PCD, with genetic testing recommended when other confirmatory diagnostic tests are less accessible. We present our experience with genetic testing as first line with a proposed algorithm for high consanguinity populations. METHODS: Patients with a suspected diagnosis of PCD underwent genetic testing according to a diagnostic algorithm composed of three steps: (1) patients with a previously known causative familial/Bedouin tribal pathogenic variant completed direct testing for a single variant; (2) if the initial test was negative or there was no known pathogenic variant, a PCD genetic panel was completed; (3) if the panel was negative, whole exome sequencing (WES) was completed. RESULTS: Since the implementation of the protocol, diagnosis was confirmed by genetic testing in 21 patients. The majority of them were of Bedouin origin (81%) and had a positive history of consanguinity (65%). Nine patients (43%) had a sibling with a confirmed diagnosis. Most patients (15/21, 71%) were diagnosed by direct pathogenic variant testing and the remainder by genetic panel (19%) and WES (10%). Disease-causing variants were found in nine genes, with DNAL1 (24%) and DNAAF3, DNAAF5, ZMYND10 (14% each) as the most prevalent ones. CONCLUSIONS: In highly consanguineous regions, a stepwise genetic testing approach is recommended. This approach may be particularly useful in areas where the ability to obtain confirmatory diagnostic tests through other modalities is less accessible.

The genetic framework of primary ciliary dyskinesia assessed by soft computing analysis.

BACKGROUND: International guidelines disagree on how best to diagnose primary ciliary dyskinesia (PCD), not least because many tests rely on pattern recognition. We hypothesized that quantitative distribution of ciliary ultrastructural and motion abnormalities would detect most frequent PCD-causing groups of genes by soft computing analysis. METHODS: Archived data on transmission electron microscopy and high-speed video analysis from 212 PCD patients were re-examined to quantitate distribution of ultrastructural (10 parameters) and functional ciliary features (4 beat pattern and 2 frequency parameters). The correlation between ultrastructural and motion features was evaluated by blinded clustering analysis of the first two principal components, obtained from ultrastructural variables for each patient. Soft computing was applied to ultrastructure to predict ciliary beat frequency (CBF) and motion patterns by a regression model. Another model classified the patients into the five most frequent PCD-causing gene groups, from their ultrastructure, CBF and beat patterns. RESULTS: The patients were subdivided into six clusters with similar values to homologous ultrastructural phenotype, motion patterns, and CBF, except for clusters 1 and 4, attributable to normal ultrastructure. The regression model confirmed the ability to predict functional ciliary features from ultrastructural parameters. The genetic classification model identified most of the different groups of genes, starting from all quantitative parameters. CONCLUSIONS: Applying soft computing methodologies to PCD diagnostic tests optimizes their value by moving from pattern recognition to quantification. The approach may also be useful to evaluate atypical PCD, and novel genetic abnormalities of unclear disease-producing potential in the future.

First preimplantation genetic testing case of Meckel syndrome with a novel homozygous TXNDC15 variant in a non-consanguineous Chinese family.

BACKGROUND: Meckel-Gruber syndrome (MKS) is a perinatally lethal, genetically heterogeneous, autosomal recessive condition caused by defective primary cilium formation. So far, the association of TXNDC15-related MKS has been reported in only five independent families from diverse ethnic origins, including Saudi, Pakistani, Estonian, and Indian. Here, we report a fetus diagnosed with MKS at 12 weeks, exhibiting typical ultrasound findings. METHODS: Low-coverage whole-genome sequencing was used to identify chromosomal abnormalities. Trio-base whole exome sequencing (trio-WES) was performed to investigate the potential pathogenic variants associated with MKS. Preimplantation genetic testing for monogenic disorders (PGT-M) was applied to prevent the transmission of the pathogenic variant. RESULTS: A novel homozygous pathogenic variant in the TXNDC15 gene was identified through trio-WES. The application of PGT-M successfully prevented the transmission of the pathogenic variant and resulted in an ongoing pregnancy. CONCLUSION: This is the first report of a TXNDC15 variant in the Chinese population and the first PGT case of TXNDC15-related MKS worldwide. The successful application of PGT-M in this family provides a potential approach for other monogenic diseases. Our case expands the variant spectrum of TXNDC15 and contributes to the molecular diagnosis and genetic counseling for MKS. This case underscores the importance of appropriate genetic testing methods and accurate genetic counseling in the diagnosis of rare monogenic diseases.

Novel homozygous mutations in TXNDC15 causing Meckel syndrome.

BACKGROUND: Meckel syndrome (MKS) is the most severe form of an autosomal recessive ciliopathy and is clinically characterized by occipital encephalocele, severely polycystic kidneys, and postaxial polydactyly (toes). The association of TXNDC15-related MKS has been reported. We report the case of a homozygous mutation in the TXNDC15 gene, causing MKS14 in the Chinese population. METHODS: The fetal skin tissue and parental peripheral blood were retained for whole-exome sequencing and Sanger sequencing, which investigated the potential pathogenic variants associated with MKS. RESULTS: The fetus was homozygous for a mutation in the TXNDC15 gene (NM_024715.3), specifically c.560delA (p.Asn187llefsTer4), and both parents were heterozygous for this mutation. CONCLUSION: Our study identified a new mutation that adds to the mutational landscape of MKS, which provide a basis for genetic counseling and the selection of reproductive options.

Impact of primary ciliary dyskinesia: Beyond sinobronchial syndrome in Japan.

Primary ciliary dyskinesia (PCD) is a rare genetic disorder characterized by impaired motile cilia function, particularly in the upper and lower airways. To date, more than 50 causative genes related to the movement, development, and maintenance of cilia have been identified. PCD mostly follows an autosomal recessive inheritance pattern, in which PCD symptoms manifest only in the presence of pathogenic variants in both alleles. Several genes causing PCD have been recently identified that neither lead to situs inversus nor cause definitive abnormalities in ciliary ultrastructure. Importantly, the distribution of disease-causing genes and pathogenic variants varies depending on ethnicity. In Japan, homozygosity for a ∼27.7-kb deletion of DRC1 is estimated to be the most common cause of PCD, presumably as a founder mutation. The clinical picture of PCD is similar to that of sinobronchial syndrome, thus making its differentiation from diffuse panbronchiolitis and other related disorders difficult. Given the diagnostic challenges, many cases remain undiagnosed or misdiagnosed, particularly in adults. While no fundamental cure is currently available, lifelong medical subsidies are provided in Japan, and proper respiratory management, along with continued prevention and treatment of infections, is believed to mitigate the decline in respiratory function. Timely action will be necessary when specific treatments for PCD become available in the future. This narrative review focuses on variations in the disease status of PCD in a non-Western country.