Primary Ciliary Dyskinesia

Primary ciliary dyskinesia (PCD) is an autosomal recessive disorder of cilia structure, function, and biogenesis leading to chronic infections of the respiratory tract, fertility problems and disorders of organ laterality. The diagnosis can be challenging, using traditional tools such as characteristic clinical features, ciliary functional and ultra-structural defects; newer screening tools such as nasal nitric oxide levels and genetic testing add to the diagnostic algorithm. There are thirty-two known PCD causing genes, and in the future, comprehensive genetic testing may screen young infants prior to developing symptoms thus improving survival. Therapies include surveillance of pulmonary function and microbiology, in addition to airway clearance, antibiotics and ideally, early referral to bronchiectasis centers. As with CF, standardized care at specialized centers using a multidisciplinary approach likely improves outcomes. In conjunction with the CF foundation, the PCD foundation, and with lead investigators and clinicians, is developing a network of PCD clinical centers to coordinate the effort in North America and Europe. As the network grows, care and knowledge will improve

Primary ciliary dyskinesia: improving the diagnostic approach

The diagnosis of primary ciliary dyskinesia (PCD) has relied on analysis of ciliary motility and ultrastructure; however, these tests are not readily available and have not been standardized. Consequently, the diagnosis of PCD may be delayed or missed or made incorrectly. This review outlines the potential utility of new diagnostic tests, including measurement of nasal nitric oxide (NO) production and systematic analysis for mutations in gene encoding ciliary proteins

The prevalence of clinical features associated with primary ciliary dyskinesia in a heterotaxy population: results of a web-based survey

Primary ciliary dyskinesia and heterotaxy are rare but not mutually exclusive disorders, which result from cilia dysfunction. Heterotaxy occurs in at least 12.1% of primary ciliary dyskinesia patients, but the prevalence of primary ciliary dyskinesia within the heterotaxy population is unknown. We designed and distributed a web-based survey to members of an international heterotaxy organisation to determine the prevalence of respiratory features that are common in primary ciliary dyskinesia and that might suggest the possibility of primary ciliary dyskinesia. A total of 49 members (25%) responded, and 37% of the respondents have features suggesting the possibility of primary ciliary dyskinesia, defined as (1) the presence of at least two chronic respiratory symptoms, or (2) bronchiectasis or history of respiratory pathogens suggesting primary ciliary dyskinesia. Of the respondents, four completed comprehensive, in-person evaluations, with definitive primary ciliary dyskinesia confirmed in one individual, and probable primary ciliary dyskinesia identified in two others. The high prevalence of respiratory features compatible with primary ciliary dyskinesia in this heterotaxy population suggests that a subset of heterotaxy patients have dysfunction of respiratory, as well as embryonic nodal cilia. To better assess the possibility of primary ciliary dyskinesia, heterotaxy patients with chronic oto-sino-respiratory symptoms should be referred for a primary ciliary dyskinesia evaluation

Primary Ciliary Dyskinesia. Recent Advances in Diagnostics, Genetics, and Characterization of Clinical Disease

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous recessive disorder of motile cilia that leads to oto-sino-pulmonary diseases and organ laterality defects in approximately 50% of cases. The estimated incidence of PCD is approximately 1 per 15,000 births, but the prevalence of PCD is difficult to determine, primarily because of limitations in diagnostic methods that focus on testing ciliary ultrastructure and function. Diagnostic capabilities have recently benefitted from (1) documentation of low nasal nitric oxide production in PCD and (2) discovery of biallelic mutations in multiple PCD-causing genes. The use of these complementary diagnostic approaches shows that at least 30% of patients with PCD have normal ciliary ultrastructure. More accurate identification of patients with PCD has also allowed definition of a strong clinical phenotype, which includes neonatal respiratory distress in >80% of cases, daily nasal congestion and wet cough starting soon after birth, and early development of recurrent/chronic middle-ear and sinus disease. Recent studies, using advanced imaging and pulmonary physiologic assessments, clearly demonstrate early onset of lung disease in PCD, with abnormal air flow mechanics by age 6–8 years that is similar to cystic fibrosis, and age-dependent onset of bronchiectasis. The treatment of PCD is not standardized, and there are no validated PCD-specific therapies. Most patients with PCD receive suboptimal management, which should include airway clearance, regular surveillance of pulmonary function and respiratory microbiology, and use of antibiotics targeted to pathogens. The PCD Foundation is developing a network of clinical centers, which should improve diagnosis and management of PCD

A New Tool Improves Diagnostic Test Performance for Transmission EM Evaluation of Axonemal Dynein Arms

Diagnosis of primary ciliary dyskinesia (PCD) by identification of dynein arm loss in transmission electron microscopy (TEM) images can be confounded by high background noise due to random electron-dense material within the ciliary matrix, leading to diagnostic uncertainty even for experienced morphologists. We developed a novel image analysis tool to average the axonemal peripheral microtubular doublets, thereby increasing microtubular signal and reducing random background noise. In a randomized, double-blinded study that compared two experienced morphologists and three different diagnostic approaches, we found that use of this tool led to improvement in diagnostic TEM test performance

Cri du Chat Syndrome and Primary Ciliary Dyskinesia: A Common Genetic Cause on Chromosome 5p

Cri du chat syndrome (CdCS) and primary ciliary dyskinesia (PCD) are rare diseases that present with frequent respiratory symptoms. PCD can be caused by hemizygous DNAH5 mutation in combination with a 5p segmental deletion attributable to CdCS on the opposite chromosome. Chronic oto-sino-pulmonary symptoms or organ laterality defects in CdCS should prompt an evaluation for PCD

Next generation massively parallel sequencing of targeted exomes to identify genetic mutations in primary ciliary dyskinesia: Implications for application to clinical testing

Advances in genetic sequencing technology have the potential to enhance testing for genes associated with genetically heterogeneous clinical syndromes, such as primary ciliary dyskinesia (PCD). The objective of this study was to investigate the performance characteristics of exon-capture technology coupled with massively parallel sequencing for clinical diagnostic evaluation

Clinical and genetic aspects of primary ciliary dyskinesia/Kartagener syndrome

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous disorder of motile cilia. Most of the disease-causing mutations identified to date involve the heavy (DNAH5) or intermediate (DNAI1) chain dynein genes in ciliary outer dynein arms, although a few mutations have been noted in other genes. Clinical molecular genetic testing for PCD is available for the most common mutations. The respiratory manifestations of PCD (chronic bronchitis leading to bronchiectasis, chronic rhino-sinusitis and chronic otitis media) reflect impaired mucociliary clearance owing to defective axonemal structure. Ciliary ultrastructural analysis in most patients (>80%) reveals defective dynein arms, although defects in other axonemal components have also been observed. Approximately 50% of PCD patients have laterality defects (including situs inversus totalis and, less commonly, heterotaxy and congenital heart disease), reflecting dysfunction of embryological nodal cilia. Male infertility is common and reflects defects in sperm tail axonemes. Most PCD patients have a history of neonatal respiratory distress, suggesting that motile cilia play a role in fluid clearance during the transition from a fetal to neonatal lung. Ciliopathies involving sensory cilia, including autosomal dominant or recessive polycystic kidney disease, Bardet-Biedl syndrome, and Alstrom syndrome, may have chronic respiratory symptoms and even bronchiectasis suggesting clinical overlap with PCD

Mutation of CFAP57, a protein required for the asymmetric targeting of a subset of inner dynein arms in Chlamydomonas, causes primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is characterized by chronic airway disease, reduced fertility, and randomization of the left/right body axis. It is caused by defects of motile cilia and sperm flagella. We screened a cohort of affected individuals that lack an obvious axonemal defect for pathogenic variants using whole exome capture, next generation sequencing, and bioinformatic analysis assuming an autosomal recessive trait. We identified one subject with an apparently homozygous nonsense variant [(c.1762C\u3eT), p.(Arg588*)] in the uncharacterized CFAP57 gene. Interestingly, the variant results in the skipping of exon 11 (58 amino acids), which may be due to disruption of an exonic splicing enhancer. In normal human nasal epithelial cells, CFAP57 localizes throughout the ciliary axoneme. Nasal cells from the PCD patient express a shorter, mutant version of CFAP57 and the protein is not incorporated into the axoneme. The missing 58 amino acids include portions of WD repeats that may be important for loading onto the intraflagellar transport (IFT) complexes for transport or docking onto the axoneme. A reduced beat frequency and an alteration in ciliary waveform was observed. Knockdown of CFAP57 in human tracheobronchial epithelial cells (hTECs) recapitulates these findings. Phylogenetic analysis showed that CFAP57 is highly conserved in organisms that assemble motile cilia. CFAP57 is allelic with the BOP2/IDA8/FAP57 gene identified previously in Chlamydomonas reinhardtii. Two independent, insertional fap57 Chlamydomonas mutant strains show reduced swimming velocity and altered waveforms. Tandem mass tag (TMT) mass spectroscopy shows that FAP57 is missing, and the g inner dyneins (DHC7 and DHC3) and the d inner dynein (DHC2) are reduced, but the FAP57 paralog FBB7 is increased. Together, our data identify a homozygous variant in CFAP57 that causes PCD that is likely due to a defect in the inner dynein arm assembly process

DYX1C1 is required for axonemal dynein assembly and ciliary motility

Dyx1c1 has been associated with dyslexia and neuronal migration in the developing neocortex. Unexpectedly, we found that deletion of Dyx1c1 exons 2–4 in mice caused a phenotype resembling primary ciliary dyskinesia (PCD), a genetically heterogeneous disorder characterized by chronic airway disease, laterality defects, and male infertility. This phenotype was confirmed independently in mice with a Dyx1c1c.T2A start codon mutation recovered from an ENU mutagenesis screen. Morpholinos targeting dyx1c1 in zebrafish also created laterality and ciliary motility defects. In humans, recessive loss-of-function DYX1C1 mutations were identified in twelve PCD individuals. Ultrastructural and immunofluorescence analyses of DYX1C1-mutant motile cilia in mice and humans revealed disruptions of outer and inner dynein arms (ODA/IDA). DYX1C1 localizes to the cytoplasm of respiratory epithelial cells, its interactome is enriched for molecular chaperones, and it interacts with the cytoplasmic ODA/IDA assembly factor DNAAF2/KTU. Thus, we propose that DYX1C1 is a newly identified dynein axonemal assembly factor (DNAAF4)