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.

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.

Les séquelles de virose en pneumopédiatrie

L’immaturité du système immunitaire explique une part de la vulnérabilité aux pathogènes respiratoires durant l’enfance. Une infection virale respiratoire aiguë chez l’enfant peut être secondaire à 1 des 200 virus génétiquement différents et identifiables par les outils moléculaires. Les cellules ciliées distribuées tout au long de l’épithélium des voies respiratoires sont la cible des virus. Les études épidémiologiques rapportent une diminution de la fonction respiratoire chez l’adulte indépendamment de facteurs confondants lorsqu’une pneumonie est survenue avant l’âge de 2 voire 7 ans. Cette réduction de la fonction respiratoire est le reflet probable de l’atteinte initiale malgré les processus de réparation (altération potentielle de croissance pulmonaire) et à l’âge adulte d’une accélération du déclin physiologique des capacités ventilatoires. Les études portant sur l’origine des dilatations des bronches retrouvent des antécédents de pneumopathies infectieuses plus d’une fois sur deux. Les infections à adénovirus sont particulièrement en cause. Une bronchiolite obstructive post-infectieuse peut survenir même chez l’enfant immunocompétent ; le tableau initial est très souvent pseudo-grippal, puis est marqué par une dissociation entre des signes fonctionnels importants et un examen clinique pauvre. L’évolution au long cours est peu prévisible mais peut conduire à l’insuffisance respiratoire chronique létale. Les pneumopathies infiltratives diffuses sont caractérisées par une infiltration diffuse de la charpente conjonctivale du poumon par des cellules inflammatoires et de la fibrose. Le rôle des virus dans son développement a été évoqué en raison de la présence d’inclusions cellulaires évoquant des particules virales dans le poumon d’enfants atteints. Enfin la plupart des études épidémiologiques soulignent l’association entre une symptomatologie sifflante secondaire à une agression virale durant l’enfance et le risque ultérieur de développement d’un asthme.

TTC12 Loss-of-Function Mutations Cause Primary Ciliary Dyskinesia and Unveil Distinct Dynein Assembly Mechanisms in Motile Cilia Versus Flagella

Cilia and flagella are evolutionarily conserved organelles whose motility relies on the outer and inner dynein arm complexes (ODAs and IDAs). Defects in ODAs and IDAs result in primary ciliary dyskinesia (PCD), a disease characterized by recurrent airway infections and male infertility. PCD mutations in assembly factors have been shown to cause a combined ODA-IDA defect, affecting both cilia and flagella. We identified four loss-of-function mutations in TTC12, which encodes a cytoplasmic protein, in four independent families in which affected individuals displayed a peculiar PCD phenotype characterized by the absence of ODAs and IDAs in sperm flagella, contrasting with the absence of only IDAs in respiratory cilia. Analyses of both primary cells from individuals carrying TTC12 mutations and human differentiated airway cells invalidated for TTC12 by a CRISPR-Cas9 approach revealed an IDA defect restricted to a subset of single-headed IDAs that are different in flagella and cilia, whereas TTC12 depletion in the ciliate Paramecium tetraurelia recapitulated the sperm phenotype. Overall, our study, which identifies TTC12 as a gene involved in PCD, unveils distinct dynein assembly mechanisms in human motile cilia versus flagella.

Caffeine treatment for bronchiolitis-related apnea in the pediatric intensive care unit

INTRODUCTION

Apnea is commonly encountered in children with bronchiolitis. Despite the lack of recommendations regarding bronchiolitis-related apnea (BRA) management, some pediatric intensive care unit (PICU) practitioners use caffeine treatment based on extrapolation from the recommendations for prematurity-related apnea management. The objectives of this study were to describe the management of BRA in our PICU, evaluate the caffeine prescription rate for this indication, and explore its potential effects on clinical outcomes.

METHODS

This was a retrospective study in a university hospital PICU between January 1st, 2009 and December 31st, 2016. All children under 1 year of age admitted to the PICU with a diagnosis of BRA were included. Patients were allocated to a control group or a caffeine group depending on the administration of caffeine.

RESULTS

In total, 54 infants were included and caffeine treatment was administered to 49 (91%) of them. Patient characteristics were similar between the two groups. Ventilatory support was initiated for 50 patients (93%). Supportive care and length of PICU stay were similar between the two groups. Caffeine was not associated with adverse events.

CONCLUSION

Caffeine treatment in BRA could be considered as a local standard practice. This retrospective study was underpowered to show any benefit of caffeine treatment on clinical outcomes. This treatment was not associated with significant adverse effects. We raised the question of the appropriate caffeine dosing regimen for BRA in this postterm population. Further studies on this topic are warranted.

Deep phenotyping, including quantitative ciliary beating parameters, and extensive genotyping in primary ciliary dyskinesia

Background

Primary ciliary dyskinesia (PCD) is a rare genetic disorder resulting in abnormal ciliary motility/structure, extremely heterogeneous at genetic and ultrastructural levels. We aimed, in light of extensive genotyping, to identify specific and quantitative ciliary beating anomalies, according to the ultrastructural phenotype.

Methods

We prospectively included 75 patients with PCD exhibiting the main five ultrastructural phenotypes (n=15/group), screened all corresponding PCD genes and measured quantitative beating parameters by high-speed video-microscopy (HSV).

Results

Sixty-eight (91%) patients carried biallelic mutations. Combined outer/inner dynein arms (ODA/IDA) defect induces total ciliary immotility, regardless of the gene involved. ODA defect induces a residual beating with dramatically low ciliary beat frequency (CBF) related to increased recovery stroke and pause durations, especially in case of DNAI1 mutations. IDA defect with microtubular disorganisation induces a low percentage of beating cilia with decreased beating angle and, in case of CCDC39 mutations, a relatively conserved mean CBF with a high maximal CBF. Central complex defect induces nearly normal beating parameters, regardless of the gene involved, and a gyrating motion in a minority of ciliated edges, especially in case of RSPH1 mutations. PCD with normal ultrastructure exhibits heterogeneous HSV values, but mostly an increased CBF with an extremely high maximal CBF.

Conclusion

Quantitative HSV analysis in PCD objectives beating anomalies associated with specific ciliary ultrastructures and genotypes. It represents a promising approach to guide the molecular analyses towards the best candidate gene(s) to be analysed or to assess the pathogenicity of the numerous sequence variants identified by next-generation-sequencing.

[Planned home versus planned hospital births: adverse outcomes comparison by reviewing the international literature]

OBJECTIVE

To assess the safety of planned home birth compared to hospital birth, in low-risk pregnancies.

METHOD

An international literature review was conducted. Mortality, adverse outcomes and medical interventions were compared.

RESULTS

Home birth was not associated with higher mortality rates, but with lower maternal adverse outcomes. Perinatal adverse outcomes are not significantly different at home and in hospital. Medical interventions are more frequent in hospital births.

CONCLUSION

Home birth attended by a well-trained midwife is not associated with increased mortality and morbidity rates, but with less medical interventions.