Primary ciliary dyskinesia: a big data genomics approach

How can the real-life frequency of a complicated condition that occurs irregularly, with a clinically variable presentation that is often difficult to diagnose, be calculated? This is a challenge for understanding the societal and medical impacts of an estimated 7000 rare disorders (those affecting more than one in 2000 people each) that can be poorly understood and often missed, especially if lacking clear-cut indicatory tests. The collective rare disease burden affects over one in 20 people, involving a disparate range of health-care services and creating unmet medical needs with potential for incorrect management. Better diagnostics and disease prevalence estimates are key to improving inequalities for millions of affected families worldwide

A high prevalence CCDC103 p.His154Pro mutation causing primary ciliary dyskinesia disrupts protein oligomerisation and is associated with normal diagnostic investigations

RATIONALE: Primary ciliary dyskinesia is a genetically heterogeneous inherited condition characterised by progressive lung disease arising from abnormal cilia function. Approximately half of patients have situs inversus. The estimated prevalence of primary ciliary dyskinesia in the UK South Asian population is 1:2265. Early, accurate diagnosis is key to implementing appropriate management but clinical diagnostic tests can be equivocal. OBJECTIVES: To determine the importance of genetic screening for primary ciliary dyskinesia in a UK South Asian population with a typical clinical phenotype, where standard testing is inconclusive. METHODS: Next-generation sequencing was used to screen 86 South Asian patients who had a clinical history consistent with primary ciliary dyskinesia. The effect of a CCDC103 p.His154Pro missense variant compared with other dynein arm-associated gene mutations on diagnostic/phenotypic variability was tested. CCDC103 p.His154Pro variant pathogenicity was assessed by oligomerisation assay. RESULT: Sixteen of 86 (19%) patients carried a homozygous CCDC103 p.His154Pro mutation which was found to disrupt protein oligomerisation. Variable diagnostic test results were obtained including normal nasal nitric oxide levels, normal ciliary beat pattern and frequency and a spectrum of partial and normal dynein arm retention. Fifteen (94%) patients or their sibling(s) had situs inversus suggesting CCDC103 p.His154Pro patients without situs inversus are missed. CONCLUSIONS: The CCDC103 p.His154Pro mutation is more prevalent than previously thought in the South Asian community and causes primary ciliary dyskinesia that can be difficult to diagnose using pathology-based clinical tests. Genetic testing is critical when there is a strong clinical phenotype with inconclusive standard diagnostic tests

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

Photoreceptor phagosome processing defects and disturbed autophagy in retinal pigment epithelium of Cln3Δex1-6 mice modelling juvenile neuronal ceroid lipofuscinosis (Batten disease)

Retinal degeneration and visual impairment are the first signs of juvenile neuronal ceroid lipofuscinosis caused by CLN3 mutations, followed by inevitable progression to blindness. We investigated retinal degeneration in Cln3Δex1-6 null mice, revealing classic ‘fingerprint’ lysosomal storage in the retinal pigment epithelium (RPE), replicating the human disease. The lysosomes contain mitochondrial F0-ATP synthase subunit c along with undigested membranes, indicating a reduced degradative capacity. Mature autophagosomes and basal phagolysosomes, the terminal degradative compartments of autophagy and phagocytosis, are also increased in Cln3Δex1-6 RPE, reflecting disruption to these key pathways that underpin the daily phagocytic turnover of photoreceptor outer segments (POS) required for maintenance of vision. The accumulated autophagosomes have post-lysosome fusion morphology, with undigested internal contents visible, while accumulated phagosomes are frequently docked to cathepsin D-positive lysosomes, without mixing of phagosomal and lysosomal contents. This suggests lysosome-processing defects affect both autophagy and phagocytosis, supported by evidence that phagosomes induced in Cln3Δex1-6-derived mouse embryonic fibroblasts have visibly disorganized membranes, unprocessed internal vesicles and membrane contents, in addition to reduced LAMP1 membrane recruitment. We propose that defective lysosomes in Cln3Δex1-6 RPE have a reduced degradative capacity that impairs the final steps of the intimately connected autophagic and phagocytic pathways that are responsible for degradation of POS. A build-up of degradative organellar by-products and decreased recycling of cellular materials is likely to disrupt processes vital to maintenance of vision by the RPE

Clinical and genetic spectrum in 33 Egyptian families with suspected primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is a rare genetic disorder of motile cilia dysfunction generally inherited as an autosomal recessive disease. Genetic testing is increasingly considered an early step in the PCD diagnostic workflow. We used targeted panel next generation sequencing (NGS) for genetic screening of 33 Egyptian families with highly clinically suspected PCD. All variants prioritized were Sanger confirmed in the affected individuals and correctly segregated within the family. Targeted NGS yielded a high diagnostic output (70%) with bi‐allelic mutations identified in known PCD genes. Mutations were identified in 13 genes overall, with CCDC40 and CCDC39 the most frequently mutated genes among Egyptian patients. Most identified mutations were predicted null effect variants (79%) and not reported before (85%). This study reveals that the genetic landscape of PCD among Egyptians is highly heterogeneous, indicating that a targeted NGS approach covering multiple genes will provide a superior diagnostic yield than Sanger sequencing for genetic diagnosis. The high diagnostic output achieved here highlights the potential of placing genetic testing early within the diagnostic workflow for PCD, in particular in developing countries where other diagnostic tests can be less available

Hydrocephalus and diffuse choroid plexus hyperplasia in primary ciliary dyskinesia-related MCIDAS mutation

OBJECTIVE: To report a neuroradiologic phenotype associated with reduced generation of multiple motile cilia (RGMC) and mutations in the multicilin gene. We hypothesize that the observed phenotype may reflect the emerging role that ependymal cilia play in regulating CSF production. METHOD: Clinical and radiologic records were retrospectively reviewed for 7 consecutive patients diagnosed by the Leicester UK national primary ciliary dyskinesia (PCD) diagnostic laboratory. RESULTS: On MRI scanning, all patients demonstrated hydrocephalus, choroid plexus hyperplasia (CPH), and arachnoid cysts. No patient had any sign of neurologic deficit. All patients had significant lung disease. CONCLUSIONS: We conclude that there is a high incidence of hydrocephalus, arachnoid cysts, and CPH in MCIDAS-associated RGMC. In all cases, the observed hydrocephalus seems arrested in childhood without progression or adverse neurologic sequelae. Our new observation of CPH, which is associated with CSF overproduction, is the first macroscopic evidence that ependymal cilia may be involved in the regulation of CSF production and flow. We suggest that brain imaging should be performed in all cases of RGMC and that a diagnosis of PCD or RGMC be strongly considered in patients with unexplained hydrocephalus and a lifelong “wet”-sounding cough

Hydrocephalus and diffuse choroid plexus hyperplasia in primary ciliary dyskinesia-related MCIDAS mutation

Objective: To report a neuroradiologic phenotype associated with reduced generation of multiple motile cilia (RGMC) and mutations in the multicilin gene. We hypothesize that the observed phenotype may reflect the emerging role that ependymal cilia play in regulating CSF production. Method: Clinical and radiologic records were retrospectively reviewed for 7 consecutive patients diagnosed by the Leicester UK national primary ciliary dyskinesia (PCD) diagnostic laboratory. Results: On MRI scanning, all patients demonstrated hydrocephalus, choroid plexus hyperplasia (CPH), and arachnoid cysts. No patient had any sign of neurologic deficit. All patients had significant lung disease. Conclusions: We conclude that there is a high incidence of hydrocephalus, arachnoid cysts, and CPH in MCIDAS-associated RGMC. In all cases, the observed hydrocephalus seems arrested in childhood without progression or adverse neurologic sequelae. Our new observation of CPH, which is associated with CSF overproduction, is the first macroscopic evidence that ependymal cilia may be involved in the regulation of CSF production and flow. We suggest that brain imaging should be performed in all cases of RGMC and that a diagnosis of PCD or RGMC be strongly considered in patients with unexplained hydrocephalus and a lifelong “wet”-sounding cough

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