Primary ciliary dyskinesia (PCD) is a rare inherited condition affecting motile cilia and leading to organ laterality defects, recurrent sino-pulmonary infections, bronchiectasis, and severe lung disease. Research over the past twenty years has revealed variability in clinical presentations, ranging from mild to more severe phenotypes. Genotype and phenotype relationships have emerged. The increasing availability of genetic panels for PCD continue to redefine these genotype-phenotype relationships and reveal milder forms of disease that had previously gone unrecognized.

DNAAF5 is a dynein motor assembly factor associated with the autosomal heterogenic recessive condition of motile cilia, primary ciliary dyskinesia (PCD). The effects of allele heterozygosity on motile cilia function are unknown. We used CRISPR-Cas9 genome editing in mice to recreate a human missense variant identified in patients with mild PCD and a second, frameshift-null deletion in Dnaaf5 . Litters with Dnaaf5 heteroallelic variants showed distinct missense and null gene dosage effects. Homozygosity for the null Dnaaf5 alleles was embryonic lethal. Compound heterozygous animals with the missense and null alleles showed severe disease manifesting as hydrocephalus and early lethality. However, animals homozygous for the missense mutation had improved survival, with partially preserved cilia function and motor assembly observed by ultrastructure analysis. Notably, the same variant alleles exhibited divergent cilia function across different multiciliated tissues. Proteomic analysis of isolated airway cilia from mutant mice revealed reduction in some axonemal regulatory and structural proteins not previously reported in DNAAF5 variants. Transcriptional analysis of mouse and human mutant cells showed increased expression of genes coding for axonemal proteins. These findings suggest allele-specific and tissue-specific molecular requirements for cilia motor assembly that may affect disease phenotypes and clinical trajectory in motile ciliopathies.

Primary ciliary dyskinesia is a rare monogenic syndrome that is associated with chronic respiratory disease, infertility, and laterality defects. Although more than 50 genes causative of primary ciliary dyskinesia have been identified, variants in the genes encoding coiled-coil domain-containing 39 (CCDC39) and CCDC40 in particular cause severe disease that is not explained by loss of ciliary motility alone. Here, we sought to understand the consequences of these variants on cellular functions beyond impaired motility. We used human cells with pathogenic variants in CCDC39 and CCDC40 , Chlamydomonas reinhardtii genetics, cryo–electron microscopy, and proteomics to define perturbations in ciliary assembly and cilia stability, as well as multiple motility-independent pathways. Analysis of proteomics of cilia from patient cells identified that the absence of the axonemal CCDC39/CCDC40 heterodimer resulted in the loss of a network of more than 90 ciliary structural proteins, including 14 that were defined as ciliary address recognition proteins, which provide docking for the missing structures. The absence of the network impaired microtubule architecture, activated cell quality control pathways, switched multiciliated cell fate to mucus-producing cells and resulted in a defective periciliary barrier. In CCDC39 variant cells, these phenotypes were reversed through expression of a normal CCDC39 transgene. These findings indicate that the CCDC39/CCDC40 heterodimer functions as a scaffold to support the assembly of an extensive network of ciliary proteins, whose loss results in both motility-dependent and motility-independent phenotypes that may explain the severity of disease. Gene therapy might be a potential treatment option to be explored in future studies.

Objectives: Evaluate the effects of an asthma de-escalation clinical pathway on selected outcomes for patients admitted to a PICU with status asthmaticus.Design: Time series quality improvement trial.Setting: PICU in a tertiary care children’s hospital.Patients: Children age 2–18 years old with a known diagnosis of asthma presenting with status asthmaticus.Intervention: One-hundred five admissions to a PICU for status asthmaticus were treated according to a new de-escalation pathway between August 15, 2015, and August 30, 2016. This group was compared with a prepathway group of 141.Measurements and Main Results: Primary outcome was variability in PICU length of stay. Secondary outcomes were median PICU length of stay, median hospital length of stay, and median duration a patient received continuous nebulized albuterol. The effectiveness of the intervention was tracked using control charts. The postpathway group demonstrated decreased variability of PICU length of stay and time receiving continuous albuterol. Statistically significant decreases were seen in median PICU length of stay (16 vs 13 hr;p= 0.0009), median duration a child spent receiving continuous nebulized albuterol (10.8 vs 7.3 hr;p= 0.0008), and median hospital length of stay (37 vs 31 hr;p= 0.02). Total number of asthma assessments completed by respiratory therapists increased from 741 to 1,087.Conclusions: Implementation of a PICU asthma de-escalation pathway demonstrated statistical decrease in the reported measures for children with status asthmaticus. Although the clinical significance of these changes may be debatable, the results demonstrate that efforts to standardize asthma care in the PICU setting is an area in need of further study.

Introduction: Childhood interstitial and diffuse lung diseases (chILD) comprise a diverse group of rare disorders. Identifying the underlying cause is crucial for treatment, prognosis, and estimating recurrence risk. The objective of this study was to assess the utilization of genetic testing for subjects enrolled in the United States National Registry for ChILD, a multicenter observational study.Methods: Genetic data from participating sites were reviewed and analyzed in relationship to clinical characteristics.Results: Of 609 children enrolled from 22 centers, genetic testing was performed for 55.5% (n = 338). Genetic testing results were positive (diagnostic) for 22.8% (n = 77), negative for 60.7% (n = 205), and uncertain for 16.6% (n = 56). Most testing was performed through gene panels (55.9%), followed by exome sequencing (ES) or whole genome sequencing (WGS) (26.9%), single gene testing (24.6%), and/or chromosomal microarray (11.8%). For participants with positive (diagnostic) genetic testing results, the majority were diagnosed through gene panel (33.8%; n = 26) or single gene testing (32.5%; n = 25). The most common diagnosis confirmed by genetic testing was SFTPC‐associated surfactant metabolism dysfunction. Of the 59 subjects with unclassified ILD, only 22% (n = 13) had undergone ES or WGS, 61% (n = 36) had received panel testing, and 27% (n = 16) did not have any genetic testing reported.Conclusion: The utilization of genetic testing has been variable in infants and children enrolled in the ChILD Registry. Additional efforts are needed to develop genetic testing recommendations for children with suspected ILD. Furthermore, there is opportunity for broader utilization of ES/WGS and genetic discovery for children with lung disease of unclear etiology.