DNAI2 mutations cause primary ciliary dyskinesia with defects in the outer dynein arm

Mutations of DNAH11 in patients with primary ciliary dyskinesia with normal ciliary ultrastructure

RATIONALE

Primary ciliary dyskinesia (PCD) is an autosomal recessive, genetically heterogeneous disorder characterised by oto-sino-pulmonary disease and situs abnormalities (Kartagener syndrome) due to abnormal structure and/or function of cilia. Most patients currently recognised to have PCD have ultrastructural defects of cilia; however, some patients have clinical manifestations of PCD and low levels of nasal nitric oxide, but normal ultrastructure, including a few patients with biallelic mutations in dynein axonemal heavy chain 11 (DNAH11).

OBJECTIVES

To test further for mutant DNAH11 as a cause of PCD, DNAH11 was sequenced in patients with a PCD clinical phenotype, but no known genetic aetiology.

METHODS

82 exons and intron/exon junctions in DNAH11 were sequenced in 163 unrelated patients with a clinical phenotype of PCD, including those with normal ciliary ultrastructure (n=58), defects in outer and/or inner dynein arms (n=76), radial spoke/central pair defects (n=6), and 23 without definitive ultrastructural results, but who had situs inversus (n=17), or bronchiectasis and/or low nasal nitric oxide (n=6). Additionally, DNAH11 was sequenced in 13 subjects with isolated situs abnormalities to see if mutant DNAH11 could cause situs defects without respiratory disease.

RESULTS

Of the 58 unrelated patients with PCD with normal ultrastructure, 13 (22%) had two (biallelic) mutations in DNAH11; and two patients without ultrastructural analysis had biallelic mutations. All mutations were novel and private. None of the patients with dynein arm or radial spoke/central pair defects, or isolated situs abnormalities, had mutations in DNAH11. Of the 35 identified mutant alleles, 24 (69%) were nonsense, insertion/deletion or loss-of-function splice-site mutations.

CONCLUSIONS

Mutations in DNAH11 are a common cause of PCD in patients without ciliary ultrastructural defects; thus, genetic analysis can be used to ascertain the diagnosis of PCD in this challenging group of patients.

Mutations in radial spoke head genes and ultrastructural cilia defects in East-European cohort of primary ciliary dyskinesia patients

Primary ciliary dyskinesia (PCD) is a rare (1/20,000), multisystem disease with a complex phenotype caused by the impaired motility of cilia/flagella, usually related to ultrastructural defects of these organelles. Mutations in genes encoding radial spoke head (RSPH) proteins, elements of the ciliary ultrastructure, have been recently described. However, the relative involvement of RSPH genes in PCD pathogenesis remained unknown, due to a small number of PCD families examined for mutations in these genes. The purpose of this study was to estimate the involvement of RSPH4A and RSPH9 in PCD pathogenesis among East Europeans (West Slavs), and to shed more light on ultrastructural ciliary defects caused by mutations in these genes. The coding sequences of RSPH4A and RSPH9 were screened in PCD patients from 184 families, using single strand conformational polymorphism analysis and sequencing. Two previously described (Q109X; R490X) and two new RSPH4A mutations (W356X; IVS3_2–5del), in/around exons 1 and 3, were identified; no mutations were found in RSPH9. We estimate that mutations in RSPH4A, but not in RSPH9, are responsible for 2–3% of cases in the East European PCD population (4% in PCD families without situs inversus; 11% in families preselected for microtubular defects). Analysis of the SNP-haplotype background provided insight into the ancestry of repetitively found mutations (Q109X; R490X; IVS3_2–5del), but further studies involving other PCD cohorts are required to elucidate whether these mutations are specific for Slavic people or spread among other European populations. Ultrastructural defects associated with the mutations were analyzed in the transmission electron microscope images; almost half of the ciliary cross-sections examined in patients with RSPH4A mutations had the microtubule transposition phenotype (9+0 and 8+1 pattern). While microtubule transposition was a prevalent ultrastructural defect in cilia from patients with RSPH4A mutations, similar defects were also observed in PCD patients with mutations in other genes.

Mutations in axonemal dynein assembly factor DNAAF3 cause primary ciliary dyskinesia

Primary Ciliary Dyskinesia (PCD) most often arises from loss of the dynein motors that power ciliary beating. Here we show that PF22/DNAAF3, a previously uncharacterized protein, is essential for the preassembly of dyneins into complexes prior to their transport into cilia. We identified loss-of-function mutations in the human DNAAF3 gene in patients from families with situs inversus and defects in assembly of inner and outer dynein arms. Zebrafish dnaaf3 knockdown likewise disrupts dynein arm assembly and ciliary motility, causing PCD phenotypes including hydrocephalus and laterality malformations. Chlamydomonas reinhardtii PF22 is exclusively cytoplasmic, and a null mutant fails to assemble outer and some inner dynein arms. Altered abundance of dynein subunits in mutant cytoplasm suggests PF22/DNAAF3 acts at a similar stage to other preassembly proteins, PF13/KTU and ODA7/LRRC50, in the dynein preassembly pathway. These results support the existence of a conserved multi-step pathway for cytoplasmic formation of assembly-competent ciliary dynein complexes.

The emerging genetics of primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is an autosomal recessive, rare, genetically heterogeneous condition characterized by oto-sino-pulmonary disease together with situs abnormalities (Kartagener syndrome) owing to abnormal ciliary structure and function. Most patients are currently diagnosed with PCD based on the presence of defective ciliary ultrastructure. However, diagnosis often remains challenging due to variability in the clinical phenotype and ciliary ultrastructural changes. Some patients with PCD have normal ciliary ultrastructure, which further confounds the diagnosis. A genetic test for PCD exists but is of limited value because it investigates only a limited number of mutations in only two genes. The genetics of PCD is complicated owing to the complexity of axonemal structure that is highly conserved through evolution, which is comprised of multiple proteins. Identifying a PCD-causing gene is challenging due to locus and allelic heterogeneity. Despite genetic heterogeneity, multiple tools have been used, and there are 11 known PCD-causing genes. All of these genes combined explain approximately 50% of PCD cases; hence, more genes need to be identified. This review briefly describes the current knowledge regarding the genetics of PCD and focuses on the methodologies used to identify novel PCD-causing genes, including a candidate gene approach using model organisms, next-generation massively parallel sequencing techniques, and the use of genetically isolated populations. In conclusion, we demonstrate the multipronged approach that is necessary to circumvent challenges due to genetic heterogeneity to uncover genetic causes of PCD.

Ciliary motility: the components and cytoplasmic preassembly mechanisms of the axonemal dyneins

Motile cilia and flagella are organelles, which function in cell motility and in the transport of fluids over the surface of cells. Motility defects often result in a rare human disease, primary ciliary dyskinesia (PCD). Cell motility depends on axonemal dynein, a molecular motor that drives the beating of cilia and flagella. The dyneins are composed of multiple subunits, which are thought to be preassembled in the cytoplasm before they are transported into cilia and flagella. Axonemal dyneins have been extensively studied in Chlamydomonas. In addition, analyses of human PCDs over the past decade, together with studies in other model animals, have identified the conserved components required for dynein assembly. Recently also, the first cytoplasmic component of dynein assembly, kintoun (ktu), was elucidated through the analysis of a medaka mutant in combination with human genetics and cell biology and biochemical studies of Chlamydomonas. The components of dynein and the proteins involved in its cytoplasmic assembly process are discussed.

A systems-biology approach to understanding the ciliopathy disorders

'Ciliopathies' are an emerging class of genetic multisystemic human disorders that are caused by a multitude of largely unrelated genes that affect ciliary structure/function. They are unified by shared clinical features, such as mental retardation, cystic kidney, retinal defects and polydactyly, and by the common localization of the protein products of these genes at or near the primary cilium of cells. With the realization that many previously disparate conditions are a part of this spectrum of disorders, there has been tremendous interest in the function of cilia in developmental signaling and homeostasis. Ciliopathies are mostly inherited as simple recessive traits, but phenotypic expressivity is under the control of numerous genetic modifiers, putting these conditions at the interface of simple and complex genetics. In this review, we discuss the ever-expanding ciliopathy field, which has three interrelated goals: developing a comprehensive understanding of genes mutated in the ciliopathies and required for ciliogenesis; understanding how the encoded proteins work together in complexes and networks to modulate activity and structure-function relationships; and uncovering signaling pathways and modifier relationships.

Loss of SPEF2 function in mice results in spermatogenesis defects and primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) results from defects in motile cilia function. Mice homozygous for the mutation big giant head (bgh) have several abnormalities commonly associated with PCD, including hydrocephalus, male infertility, and sinusitis. In the present study, we use a variety of histopathological and cell biological techniques to characterize the bgh phenotype, and we identify the bgh mutation using a positional cloning approach. Histopathological, immunofluorescence, and electron microscopic analyses demonstrate that the male infertility results from shortened flagella and disorganized axonemal and accessory structures in elongating spermatids and mature sperm. In addition, there is a reduced number of elongating spermatids during spermatogenesis and mature sperm in the epididymis. Histological analyses show that the hydrocephalus is characterized by severe dilatation of the lateral ventricles and that bgh sinuses have an accumulation of mucus infiltrated by neutrophils. In contrast to the sperm phenotype, electron microscopy demonstrates that mutant respiratory epithelial cilia are ultrastructurally normal, but video microscopic analysis shows that their beat frequency is lower than that of wild-type cilia. Through a positional cloning approach, we identified two sequence variants in the gene encoding sperm flagellar protein 2 (SPEF2), which has been postulated to play an important role in spermatogenesis and flagellar assembly. A causative nonsense mutation was validated by Western blot analysis, strongly suggesting that the bgh phenotype results from the loss of SPEF2 function. Taken together, the data in this study demonstrate that SPEF2 is required for cilia function and identify a new genetic cause of PCD in mice.

Sperm flagella: comparative and phylogenetic perspectives of protein components

Sperm motility is necessary for the transport of male DNA to eggs in species with both external and internal fertilization. Flagella comprise several proteins for generating and regulating motility. Central cytoskeletal structures called axonemes have been well conserved through evolution. In mammalian sperm flagella, two accessory structures (outer dense fiber and the fibrous sheath) surround the axoneme. The axonemal bend movement is based on the active sliding of axonemal doublet microtubules by the molecular motor dynein, which is divided into outer and inner arm dyneins according to positioning on the doublet microtubule. Outer and inner arm dyneins play different roles in the production and regulation of flagellar motility. Several regulatory mechanisms are known for both dyneins, which are important in motility activation and chemotaxis at fertilization. Although dynein itself has certain properties that contribute to the formation and propagation of flagellar bending, other axonemal structures-specifically, the radial spoke/central pair apparatus-have essential roles in the regulation of flagellar bending. Recent genetic and proteomic studies have explored several new components of axonemes and shed light on the generation and regulation of sperm motility during fertilization.

[The importance of model organisms to study cilia and flagella biology]

Cilia and flagella are ubiquitous organelles that protrude from the surfaces of many cells, and whose architecture is highly conserved from protists to humans. These complex organelles, composed of over 500 proteins, can be either immotile or motile. They are involved in a myriad of biological processes, including sensing (non-motile cilia) and/or cell motility or movement of extracellular fluids (motile cilia). The ever-expanding list of human diseases linked to defective cilia illustrates the functional importance of cilia and flagella. These ciliopathies are characterised by an impressive diversity of symptoms and an often complex genetic etiology. A precise knowledge of cilia and flagella biology is thus critical to better understand these pathologies. However, multi-ciliated cells are terminally differentiated and difficult to manipulate, and a primary cilium is assembled only when the cell exits from the cell cycle. In this context the use of model organisms, that relies on the high degree of structural but also of molecular conservation of these organelles across evolution, is instrumental to decipher the many facets of cilia and flagella biology. In this review, we highlight the specific strengths of the main model organisms to investigate the molecular composition, mode of assembly, sensing and motility mechanisms and functions of cilia and flagella. Pioneering studies carried out in the green alga Chlamydomonas established the link between cilia and several genetic diseases. Moreover, multicellular organisms such as mouse, zebrafish, Xenopus, C. elegans or Drosophila, and protists like Paramecium, Tetrahymena and Trypanosoma or Leishmania each bring specific advantages to the study of cilium biology. For example, the function of genes involved in primary ciliary dyskinesia (due to defects in ciliary motility) can be efficiently assessed in trypanosomes.

Population specificity of the DNAI1 gene mutation spectrum in primary ciliary dyskinesia (PCD)

Background

Mutations in the DNAI1 gene, encoding a component of outer dynein arms of the ciliary apparatus, are the second most important genetic cause of primary ciliary dyskinesia (PCD), the genetically heterogeneous recessive disorder with the prevalence of ~1/20,000. The estimates of the DNAI1 involvement in PCD pathogenesis differ among the reported studies, ranging from 4% to 10%.

Methods

The coding sequence of DNAI1 was screened (SSCP analysis and direct sequencing) in a group of PCD patients (157 families, 185 affected individuals), the first ever studied large cohort of PCD patients of Slavic origin (mostly Polish); multiplex ligation-dependent probe amplification (MLPA) analysis was performed in a subset of ~80 families.

Results

Three previously reported mutations (IVS1+2-3insT, L513P and A538T) and two novel missense substitutions (C388Y and G515S) were identified in 12 families (i.e. ~8% of non-related Polish PCD patients). The structure of background SNP haplotypes indicated common origin of each of the two most frequent mutations, IVS1+2-3insT and A538T. MLPA analysis did not reveal any significant differences between patients and control samples. The Polish cohort was compared with all the previously studied PCD groups (a total of 487 families): IVS1+2-3insT remained the most prevalent pathogenetic change in DNAI1 (54% of the mutations identified worldwide), and the increased global prevalence of A538T (14%) was due to the contribution of the Polish cohort.

Conclusions

The worldwide involvement of DNAI1 mutations in PCD pathogenesis in families not preselected for ODA defects ranges from 7 to 10%; this global estimate as well as the mutation profile differs in specific populations. Analysis of the background SNP haplotypes suggests that the increased frequency of chromosomes carrying A538T mutations in Polish patients may reflects local (Polish or Slavic) founder effect. Results of the MLPA analysis indicate that no large exonic deletions are involved in PCD pathogenesis.

Gene expression studies in cells from primary ciliary dyskinesia patients identify 208 potential ciliary genes

Cilia are small cellular projections that either act as sensors (primary cilia) or propel fluid over the epithelia of various organs (motile cilia). The organellum has gained much attention lately because of its involvement in a group of human diseases called ciliopathies. Primary ciliary dyskinesia (PCD) is an autosomal recessive ciliopathy caused by mutations in cilia motility genes. The disease is characterized by recurrent respiratory tract infections due to the lack of an efficient mucociliary clearance. We performed whole-genome gene expression profiling in bronchial biopsies from PCD patients. We used the quality threshold clustering algorithm to identify groups of genes that revealed highly correlated RNA expression patterns in the biopsies. The largest cluster contained 372 genes and was significantly enriched for genes related to cilia. The database and literature search showed that 164 genes in this cluster were known cilia genes, strongly indicating that the remaining 208 genes were likely to be new cilia genes. The tissue expression pattern of the 208 new cilia genes and the 164 known genes was consistent with the presence of motile cilia in a given tissue. The analysis of the upstream promotor sequences revealed evidence for RFX transcription factors binding site motif in both subgroups. Based on the correlated expression patterns in PCD-affected tissues, we identified 208 genes that we predict to be involved in cilia biology. Our predictions are based directly on the human material and not on model organisms. This list of genes provides candidate genes for PCD and other ciliopathies.

In vitro culturing of ciliary respiratory cells--a model for studies of genetic diseases

Primary ciliary dyskinesia (PCD) is a rare genetic disorder caused by the impaired functioning of ciliated cells. Its diagnosis is based on the analysis of the structure and functioning of cilia present in the respiratory epithelium (RE) of the patient. Abnormalities of cilia caused by hereditary mutations closely resemble and often overlap with defects induced by the environmental factors. As a result, proper diagnosis of PCD is difficult and may require repeated sampling of patients' tissue, which is not always possible. The culturing of differentiated cells and tissues derived from the human RE seems to be the best way to diagnose PCD, to study genotype-phenotype relations of genes involved in ciliary dysfunction, as well as other aspects related to the functioning of the RE. In this review, different methods of culturing differentiated cells and tissues derived from the human RE, along with their potential and limitations, are summarized. Several considerations with respect to the factors influencing the process of in vitro differentiation (cell-to-cell interactions, medium composition, cell-support substrate) are also discussed.

Mechanisms of mammalian ciliary motility: Insights from primary ciliary dyskinesia genetics

Motile cilia and flagella are organelles that, historically, have been poorly understood and inadequately investigated. However, cilia play critical roles in fluid clearance in the respiratory system and the brain, and flagella are required for sperm motility. Genetic studies involving human patients and mouse models of primary ciliary dyskinesia over the last decade have uncovered a number of important ciliary proteins and have begun to elucidate the mechanisms underlying ciliary motility. When combined with genetic, biochemical, and cell biological studies in Chlamydomonas reinhardtii, these mammalian genetic analyses begin to reveal the mechanisms by which ciliary motility is regulated.

Oda16/Wdr69 is essential for axonemal dynein assembly and ciliary motility during zebrafish embryogenesis

In the alga Chlamydomonas reinhardtii, Oda16 functions during ciliary assembly as an adaptor for intraflagellar transport of outer arm dynein. Oda16 orthologs only occur in genomes of organisms that use motile cilia; however, such cilia play multiple roles during vertebrate development and the contribution of Oda16 to their assembly remains unexplored. We demonstrate that the zebrafish Oda16 ortholog (Wdr69) is expressed in organs with motile cilia and retains a role in dynein assembly. Antisense morpholino knockdown of Wdr69 disrupts ciliary motility and results in multiple phenotypes associated with vertebrate ciliopathies. Affected cilia included those in Kupffer's vesicle, where Wdr69 plays a role in generation of asymmetric fluid flow and establishment of organ laterality, and otic vesicles, where Wdr69 is needed to develop normal numbers of otoliths. Analysis of cilium ultrastructure revealed loss of outer dynein arms in morphant embryos. These results support a remarkable level of functional conservation for Oda16/Wdr69.

Amyotrophic lateral sclerosis in a patient with Kartagener syndrome

We present a case of a patient with clinically definite ALS, who had earlier suffered from Kartagener syndrome, which is characterized by the triad comprising chronic sinusitis, bronchiectasis, and situs inversus. Recent linkage and mutational analyses identified several genes that are responsible for Kartagener syndrome. Most of them encode subunits of axonemal dyneins, highlighting the importance of dynein motors to ciliary motility. Recent data indicate that defects in cytoplasmic dynein-mediated retrograde axonal transport are involved in the etiology of ALS. Genes encoding the dynein heavy chain of cytoplasmic and outer arm axonemal dyneins are reported to have similar sequences in their central and 3'-end regions. Although a causal link between ALS and Kartagener syndrome has not yet been definitely established, the precise relationship between disrupted axonemal dynein function in Kartagener syndrome and motor neuron death should be investigated.

An outer arm Dynein conformational switch is required for metachronal synchrony of motile cilia in planaria

Here we use the motile ventral cilia of the planarian S. mediterranea to examine the role of outer arm dynein in the generation and maintenance of metachronal synchrony. We demonstrate that a single dynein light chain plays a mechanosensory role necessary to entrain and maintain the metachronal synchrony of motile cilia.

Motile cilia mediate the flow of mucus and other fluids across the surface of specialized epithelia in metazoans. Efficient clearance of peri-ciliary fluids depends on the precise coordination of ciliary beating to produce metachronal waves. The role of individual dynein motors and the mechanical feedback mechanisms required for this process are not well understood. Here we used the ciliated epithelium of the planarian Schmidtea mediterranea to dissect the role of outer arm dynein motors in the metachronal synchrony of motile cilia. We demonstrate that animals that completely lack outer dynein arms display a significant decline in beat frequency and an inability of cilia to coordinate their oscillations and form metachronal waves. Furthermore, lack of a key mechanosensitive regulatory component (LC1) yields a similar phenotype even though outer arms still assemble in the axoneme. The lack of metachrony was not due simply to a decrease in ciliary beat frequency, as reducing this parameter by altering medium viscosity did not affect ciliary coordination. In addition, we did not observe a significant temporal variability in the beat cycle of impaired cilia. We propose that this conformational switch provides a mechanical feedback system within outer arm dynein that is necessary to entrain metachronal synchrony.

Zilienkrankheiten unter besonderer Berücksichtigung der primären ziliären Dyskinesie

Die primäre ziliäre Dyskinesie („primary ciliary dyskinesia“, PCD) ist eine klinisch und genetisch heterogene Gruppe von Erkrankungen. Der Phänotyp der Erkrankung erklärt sich durch angeborene Defekte motiler respiratorischer Flimmerhärchen (Zilien), die zu einer verminderten mukoziliären Reinigung der Atemwege führt. Bei den meisten PCD-Varianten kommt es zu einer Randomisierung der Links-rechts-Körperasymmetrie, da nodale Zilien während der frühen embryonalen Entwicklung ebenfalls eine Dysmotilität aufweisen. Etwa die Hälfte der PCD-Patienten weisen daher einen Situs inversus (Kartagener-Syndrom) oder eine Heterotaxie auf. Mittlerweile konnten Mutationen in 9 Genen, die für axonemale Motorproteine oder zytoplasmatische Assemblierungsfaktoren kodieren, nachgewiesen werden. Für 2 X-chromosomale syndromale PCD-Varianten, die entweder mit Retinitis pigmentosa oder mentaler Retardierung einhergehen, wurden die Gendefekte aufgeklärt. Bei klinischem Verdacht sollte die Diagnose mittels Hochfrequenzvideomikroskopie (Zilienschlaganalyse) gesichert werden. Nicht alle PCD-Varianten weisen elektronenmikroskopische oder immunfluoreszenzmikroskopische Defekte auf. Die detaillierte Diagnostik erlaubt dann eine gezielte genetische Diagnostik.

Dynein axonemal intermediate chain 2 is required for formation of the left-right body axis and kidney in medaka

Ciliary defects lead to various diseases, such as primary ciliary dyskinesia (PCD) and polycystic kidney disease (PKD). We isolated a medaka mutant mii, which exhibits defects in the left-right (LR) polarity of organs, and found that mii encodes dynein axonemal intermediate chain 2a (dnai2a). Ortholog mutations were recently reported to cause PCD in humans. mii mutant embryos exhibited loss of nodal flow in Kupffer's Vesicle (KV), which is equivalent to the mammalian node, and abnormal expression of the left-specific gene. KV cilia in the mii mutant were defective in their outer dynein arms (ODAs), indicating that Dnai2a is required for ODA formation in KV cilia. While the mii mutant retained motility of the renal cilia and failed to show PKD, the loss of dnai2a and another dnai2 ortholog dnai2b led to PKD. These findings demonstrate that Dnai2 proteins control LR polarity and kidney formation through regulation of ciliary motility.

The molecular basis of human retinal and vitreoretinal diseases

During the last two to three decades, a large body of work has revealed the molecular basis of many human disorders, including retinal and vitreoretinal degenerations and dysfunctions. Although belonging to the group of orphan diseases, they affect probably more than two million people worldwide. Most excitingly, treatment of a particular form of congenital retinal degeneration is now possible. A major advantage for treatment is the unique structure and accessibility of the eye and its different components, including the vitreous and retina. Knowledge of the many different eye diseases affecting retinal structure and function (night and colour blindness, retinitis pigmentosa, cone and cone rod dystrophies, photoreceptor dysfunctions, as well as vitreoretinal traits) is critical for future therapeutic development. We have attempted to present a comprehensive picture of these disorders, including biological, clinical, genetic and molecular information. The structural organization of the review leads the reader through non-syndromic and syndromic forms of (i) rod dominated diseases, (ii) cone dominated diseases, (iii) generalized retinal degenerations and (iv) vitreoretinal disorders, caused by mutations in more than 165 genes. Clinical variability and genetic heterogeneity have an important impact on genetic testing and counselling of affected families. As phenotypes do not always correlate with the respective genotypes, it is of utmost importance that clinicians, geneticists, counsellors, diagnostic laboratories and basic researchers understand the relationships between phenotypic manifestations and specific genes, as well as mutations and pathophysiologic mechanisms. We discuss future perspectives.

Clinical Review#: State of the art for genetic testing of infertile men

Intracytoplasmic sperm injection (ICSI) now provides fertility in many cases of severe idiopathic spermatogenic failure and obstructive azoospermia. Genetic causes must be sought by systematic evaluation of infertile men and affected couples informed about the implications of such diagnoses for assisted reproductive technology outcome and their potential offspring. This review discusses established and emerging genetic disorders related to fertility practice. Chromosomal anomalies are found in about 7% men with idiopathic spermatogenic failure, predominantly numerical/structural in azoospermic men and translocations/inversions in oligospermic men. Routine karyotyping of men with sperm densities less than 10 million/ml, even in the absence of other clinical presentations, is recommended because infertility is associated with higher rates of aneuploidy in ejaculated or testicular sperm and increased chromosomal defects in ICSI offspring. The long arm of the Y chromosome microdeletions are the most common recognized genetic cause of infertility and are found in about 4% men with sperm densities less than 5 million/ml. Routine testing using strict quality assurance procedures is recommended. Azoospermia factor (AZF)-c deletions, the most common form of the long arm of the Y chromosome microdeletions, are usually associated with low levels of sperm in the ejaculate or in testis biopsies, whereas men with AZFa or AZFb+c deletions usually produce no testicular sperm. When AZF-deleted sperm are available and used for ICSI, fertility defects in male offspring seem inevitable. Bilateral congenital absence of the vas is associated with heterozygosity for cystic fibrosis transmembrane receptor mutations making routine gene screening and genetic counseling of the couple essential. Testing for less common genetic associations/defects linked with different reproductive dysfunction may be applicable to specific patients but have not entered routine practice.

Founder mutation(s) in the RSPH9 gene leading to primary ciliary dyskinesia in two inbred Bedouin families

A rare mutation in the RSPH9 gene leading to primary ciliary dyskinesia was previously identified in two Bedouin families, one from Israel and one from the United Arab Emirates (UAE). Herein we analyse mutation segregation in the Israeli family, present the clinical disease spectrum, and estimate mutation age in the two families. Mutation segregation was studied by restriction fragment length analysis. Mutation ages were estimated using a model of the decrease in the length of ancestral haplotypes. The mutations in each of the two families had a common ancestor less than 95 and less than 17 generations in the past. If the mutations in the two families are descended from a common ancestor, that mutation would have to have arisen at least 150 generations ago. If the Bedouin population has been roughly constant in size for at least 6000 years, it is possible that the mutations in the two families are identical by descent. If there were substantial fluctuations in the size of the Bedouin population, it is more likely that there were two independent mutations. Based on the available data, the population genetic analysis does not strongly favour one conclusion over the other.

Cildb: a knowledgebase for centrosomes and cilia

Ciliopathies, pleiotropic diseases provoked by defects in the structure or function of cilia or flagella, reflect the multiple roles of cilia during development, in stem cells, in somatic organs and germ cells. High throughput studies have revealed several hundred proteins that are involved in the composition, function or biogenesis of cilia. The corresponding genes are potential candidates for orphan ciliopathies. To study ciliary genes, model organisms are used in which particular questions on motility, sensory or developmental functions can be approached by genetics. In the course of high throughput studies of cilia in Paramecium tetraurelia, we were confronted with the problem of comparing our results with those obtained in other model organisms. We therefore developed a novel knowledgebase, Cildb, that integrates ciliary data from heterogeneous sources. Cildb links orthology relationships among 18 species to high throughput ciliary studies, and to OMIM data on human hereditary diseases. The web interface of Cildb comprises three tools, BioMart for complex queries, BLAST for sequence homology searches and GBrowse for browsing the human genome in relation to OMIM information for human diseases. Cildb can be used for interspecies comparisons, building candidate ciliary proteomes in any species, or identifying candidate ciliopathy genes.

Database URL:http://cildb.cgm.cnrs-gif.fr

Deletions and point mutations of LRRC50 cause primary ciliary dyskinesia due to dynein arm defects

Genetic defects affecting motility of cilia and flagella cause chronic destructive airway disease, randomization of left-right body asymmetry, and, frequently, male infertility in primary ciliary dyskinesia (PCD). The most frequent defects involve outer and inner dynein arms (ODAs and IDAs) that are large multiprotein complexes responsible for cilia-beat generation and regulation, respectively. Here, we demonstrate that large genomic deletions, as well as point mutations involving LRRC50, are responsible for a distinct PCD variant that is characterized by a combined defect involving assembly of the ODAs and IDAs. Functional analyses showed that LRRC50 deficiency disrupts assembly of distally and proximally DNAH5- and DNAI2-containing ODA complexes, as well as DNALI1-containing IDA complexes, resulting in immotile cilia. On the basis of these findings, we assume that LRRC50 plays a role in assembly of distinct dynein-arm complexes.

Loss-of-function mutations in the human ortholog of Chlamydomonas reinhardtii ODA7 disrupt dynein arm assembly and cause primary ciliary dyskinesia

Cilia and flagella are evolutionarily conserved structures that play various physiological roles in diverse cell types. Defects in motile cilia result in primary ciliary dyskinesia (PCD), the most prominent ciliopathy, characterized by the association of respiratory symptoms, male infertility, and, in nearly 50% of cases, situs inversus. So far, most identified disease-causing mutations involve genes encoding various ciliary components, such those belonging to the dynein arms that are essential for ciliary motion. Following a candidate-gene approach based on data from a mutant strain of the biflagellated alga Chlamydomonas reinhardtii carrying an ODA7 defect, we identified four families with a PCD phenotype characterized by the absence of both dynein arms and loss-of-function mutations in the human orthologous gene called LRRC50. Functional analyses performed in Chlamydomonas reinhardtii and in another flagellated protist, Trypanosoma brucei, support a key role for LRRC50, a member of the leucine-rich-repeat superfamily, in cytoplasmic preassembly of dynein arms.

Non-cystic fibrosis bronchiectasis: review and recent advances

Bronchiectasis is an abnormal dilatation of bronchi and bronchioles associated with repeated cycles of airway infection and inflammation. This review will focus on non-cystic fibrosis bronchiectasis in children, with regard to etiology, diagnosis, treatment options, and recent advances.

Clinical and genetic aspects of primary ciliary dyskinesia/Kartagener syndrome

Primary ciliary dyskinesia is a genetically heterogeneous disorder of motile cilia. Most of the disease-causing mutations identified to date involve the heavy (dynein axonemal heavy chain 5) or intermediate(dynein axonemal intermediate chain 1) chain dynein genes in ciliary outer dynein arms, although a few mutations have been noted in other genes. Clinical molecular genetic testing for primary ciliary dyskinesia is available for the most common mutations. The respiratory manifestations of primary ciliary dyskinesia (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 patients with primary ciliary dyskinesia 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 patients with primary ciliary dyskinesia 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 primary ciliary dyskinesia.

Primary ciliary dyskinesia: improving the diagnostic approach

PURPOSE OF REVIEW

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 production and systematic analysis for mutations in genes encoding ciliary proteins.

RECENT FINDINGS

Clinical manifestations of PCD have been expanded to include neonatal respiratory distress and heterotaxy. Measurement of nasal nitric oxide has emerged as a useful screening test for PCD based on the very low levels in PCD (approximately 1/10 of normal values). Genetic testing is emerging for PCD and demonstrates extensive genetic heterogeneity. Some genes and gene mutations involved in PCD have been defined. Approximately one-third of PCD cases have identifiable gene mutations in one of six different genes. An international effort is focused on defining PCD-causing defects in other genes.

SUMMARY

The incorporation of nasal nitric oxide measurement as a screening test to define probable PCD cases and gene mutation analysis to make a definitive diagnosis of PCD should enhance diagnostic evaluation of PCD.

Ciliary defects and genetics of primary ciliary dyskinesia

Cilia are evolutionarily conserved structures that play key roles in diverse cell types. Motile cilia are involved in the most prominent ciliopathy called primary ciliary dyskinesia (PCD) that combines respiratory symptoms, male infertility, and, in nearly 50% cases, situs inversus. The diagnosis of PCD relies on the identification of ciliary abnormalities that mainly concern outer and/or inner dynein arms (ODA, IDA). PCD is a genetic condition, usually inherited as an autosomal recessive trait. To date, six genes have been clearly implicated in PCD. Two "major" genes, DNAI1 and DNAH5, underlie PCD in nearly half of the patients with ODA defects, whereas RPGR, DNAH11 and TXNDC3 are implicated in rare families with specific phenotypes (retinitis pigmentosa, abnormal beating of structurally normal cilia, and situs ambiguous, respectively). The relative contribution of DNAI2 is currently being assessed. In all the other patients with ODA or other ultrastructural defects, the causative genes remain to be identified.

The dynamic cilium in human diseases

Cilia are specialized organelles protruding from the cell surface of almost all mammalian cells. They consist of a basal body, composed of two centrioles, and a protruding body, named the axoneme. Although the basic structure of all cilia is the same, numerous differences emerge in different cell types, suggesting diverse functions. In recent years many studies have elucidated the function of 9+0 primary cilia. The primary cilium acts as an antenna for the cell, and several important pathways such as Hedgehog, Wnt and planar cell polarity (PCP) are transduced through it. Many studies on animal models have revealed that during embryogenesis the primary cilium has an essential role in defining the correct patterning of the body. Cilia are composed of hundreds of proteins and the impairment or dysfunction of one protein alone can cause complete loss of cilia or the formation of abnormal cilia. Mutations in ciliary proteins cause ciliopathies which can affect many organs at different levels of severity and are characterized by a wide spectrum of phenotypes. Ciliary proteins can be mutated in more than one ciliopathy, suggesting an interaction between proteins. To date, little is known about the role of primary cilia in adult life and it is tempting to speculate about their role in the maintenance of adult organs. The state of the art in primary cilia studies reveals a very intricate role. Analysis of cilia-related pathways and of the different clinical phenotypes of ciliopathies helps to shed light on the function of these sophisticated organelles. The aim of this review is to evaluate the recent advances in cilia function and the molecular mechanisms at the basis of their activity.

Ciliary beating recovery in deficient human airway epithelial cells after lentivirus ex vivo gene therapy

Primary Ciliary Dyskinesia is a heterogeneous genetic disease that is characterized by cilia dysfunction of the epithelial cells lining the respiratory tracts, resulting in recurrent respiratory tract infections. Despite lifelong physiological therapy and antibiotics, the lungs of affected patients are progressively destroyed, leading to respiratory insufficiency. Recessive mutations in Dynein Axonemal Intermediate chain type 1 (DNAI1) gene have been described in 10% of cases of Primary Ciliary Dyskinesia. Our goal was to restore normal ciliary beating in DNAI1–deficient human airway epithelial cells. A lentiviral vector based on Simian Immunodeficiency Virus pseudotyped with Vesicular Stomatitis Virus Glycoprotein was used to transduce cultured human airway epithelial cells with a cDNA of DNAI1 driven by the Elongation Factor 1 promoter. Transcription and translation of the transduced gene were tested by RT–PCR and western blot, respectively. Human airway epithelial cells that were DNAI1–deficient due to compound heterozygous mutations, and consequently had immotile cilia and no outer dynein arm, were transduced by the lentivirus. Cilia beating was recorded and electron microscopy of the cilia was performed. Transcription and translation of the transduced DNAI1 gene were detected in human cells treated with the lentivirus. In addition, immotile cilia recovered a normal beat and outer dynein arms reappeared. We demonstrated that it is possible to obtain a normalization of ciliary beat frequency of deficient human airway epithelial cells by using a lentivirus to transduce cells with the therapeutic gene. This preliminary step constitutes a conceptual proof that is indispensable in the perspective of Primary Ciliary Dyskinesia's in vivo gene therapy. This is the first time that recovery of cilia beating is demonstrated in this disease.

This manuscript reports on a successful gene therapy attempt on human airway epithelial cells of a patient suffering from Primary Ciliary Dyskinesia. In this autosomal recessive disease, cilia of the epithelial cells that border the upper and lower respiratory tracks are not functioning. As a result, patients suffer from recurrent airway infections leading progressively to respiratory insufficiency. There is no treatment as of today that could restore normal ciliary beating. In this report, we showed that it is feasible to transfer a therapeutic gene to human airway epithelial cells with a lentivirus. This transferred gene is transcribed and expressed. Moreover, defective cells that had immotile cilia due to compound heterozygous mutations in the DNAI1 gene recovered ciliary beating after treatment with a lentivirus containing a normal DNAI1 gene. This is the first report on gene therapy in Primary Ciliary Dyskinesia. Since lentivirus is able to insert therapeutic genes into the cell genome, this result may have impact on in vivo gene therapy in this disease and in diseases related to human epithelial airway cells such as cystic fibrosis.

Ziliopathien

Zilien erfüllen viele unterschiedliche Funktionen, sie dienen als Mechano-, Chemo- und Osmosensoren und spielen bei zahlreichen Signalwegen, für eine adäquate Organentwicklung, für die Aufrechterhaltung der Gewebehomöostase und bei grundsätzlichen Entwicklungsprozessen eine wichtige Rolle. Die meisten Zelltypen im Körper weisen primäre Zilien auf, motile Zilien kommen v. a. im Respirationstrakt, ependymal in den Hirnventrikeln sowie auf Eileiterepithelien vor. Mit einem Funktionsverlust der Zilien einhergehende Krankheiten werden als Ziliopathien bezeichnet. Im vorliegenden Beitrag werden einige Erkrankungen, wie die primäre ziliäre Dyskinesie (PCD) oder polyzystische Nierenerkrankungen (PKD) und hier insbesondere die ADPKD (autosomal-dominante PKD), vorgestellt. Zudem werden die bisher identifizierten Gene, die bei der Pathogenese von Ziliopathien eine Rolle spielen, vorgestellt. Dabei verursachen viele der Genmutationen mehr als nur eine Erkrankung, und viele der aufgeführten Merkmale kommen bei verschiedenen Krankheiten vor.

Mutations in radial spoke head protein genes RSPH9 and RSPH4A cause primary ciliary dyskinesia with central-microtubular-pair abnormalities

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous inherited disorder arising from dysmotility of motile cilia and sperm. This is associated with a variety of ultrastructural defects of the cilia and sperm axoneme that affect movement, leading to clinical consequences on respiratory-tract mucociliary clearance and lung function, fertility, and left-right body-axis determination. We performed whole-genome SNP-based linkage analysis in seven consanguineous families with PCD and central-microtubular-pair abnormalities. This identified two loci, in two families with intermittent absence of the central-pair structure (chromosome 6p21.1, Zmax 6.7) and in five families with complete absence of the central pair (chromosome 6q22.1, Zmax 7.0). Mutations were subsequently identified in two positional candidate genes, RSPH9 on chromosome 6p21.1 and RSPH4A on chromosome 6q22.1. Haplotype analysis identified a common ancestral founder effect RSPH4A mutation present in UK-Pakistani pedigrees. Both RSPH9 and RSPH4A encode protein components of the axonemal radial spoke head. In situ hybridization of murine Rsph9 shows gene expression restricted to regions containing motile cilia. Investigation of the effect of knockdown or mutations of RSPH9 orthologs in zebrafish and Chlamydomonas indicate that radial spoke head proteins are important in maintaining normal movement in motile, "9+2"-structure cilia and flagella. This effect is rescued by reintroduction of gene expression for restoration of a normal beat pattern in zebrafish. Disturbance in function of these genes was not associated with defects in left-right axis determination in humans or zebrafish.