Genetic variants of small airways and interstitial pulmonary disease in children

Emerging cell and molecular targets for treating mucus hypersecretion in asthma

Mucus provides a protective barrier that is crucial for host defense in the lungs. However, excessive or abnormal mucus can have pathophysiological consequences in many pulmonary diseases, including asthma. Patients with asthma are treated with agents that relax airway smooth muscle and reduce airway inflammation, but responses are often inadequate. In part, this is due to the inability of existing therapeutic agents to directly target mucus. Accordingly, there is a critical need to better understand how mucus hypersecretion and airway plugging are affected by the epithelial cells that synthesize, secrete, and transport mucus components. This review highlights recent advances in the biology of mucin glycoproteins with a specific focus on MUC5AC and MUC5B, the chief macromolecular components of airway mucus. An improved mechanistic understanding of key steps in mucin production and secretion will help reveal novel potential therapeutic strategies.

Pulmonary Hypertension in Developmental Lung Diseases

Diverse genetic developmental lung diseases can present in the neonatal period with hypoxemic respiratory failure, often associated with with pulmonary hypertension. Intractable hypoxemia and lack of sustained response to medical management should increase the suspicion of a developmental lung disorder. Genetic diagnosis and lung biopsy are helpful in establishing the diagnosis. Early diagnosis can result in optimizing management and redirecting care if needed. This article reviews normal lung development, various developmental lung disorders that can result from genetic abnormalities at each stage of lung development, their clinical presentation, management, prognosis, and differential diagnoses.

Hereditary Mucin Deficiency Caused by Biallelic Loss of Function of MUC5B

Rationale: Mucin homeostasis is fundamental to airway health. Upregulation of airway mucus glycoprotein MUC5B is observed in diverse common lung diseases and represents a potential therapeutic target. In mice, Muc5b is required for mucociliary clearance and for controlling inflammation after microbial exposure. The consequences of its loss in humans are unclear. Objectives: The goal of this study was to identify and characterize a family with congenital absence of MUC5B protein. Methods: We performed whole-genome sequencing in an adult proband with unexplained bronchiectasis, impaired pulmonary function, and repeated Staphylococcus aureus infection. Deep phenotyping over a 12-year period included assessments of pulmonary radioaerosol mucociliary clearance. Genotyping with reverse phenotyping was organized for eight family members. Extensive experiments, including immunofluorescence staining and mass spectrometry for mucins, were performed across accessible sample types. Measurements and Main Results: The proband, and her symptomatic sibling who also had extensive sinus disease with nasal polyps, were homozygous for a novel splicing variant in the MUC5B gene (NM_002458.2: c.1938 + 1G>A). MUC5B was absent from saliva, sputum, and nasal samples. Mucociliary clearance was impaired in the proband, and large numbers of apoptotic macrophages were present in sputum. Three siblings heterozygous for the familial MUC5B variant were asymptomatic but had a shared pattern of mild lung function impairments. Conclusions: Congenital absence of MUC5B defines a new category of genetic respiratory disease. The human phenotype is highly concordant with that of the Muc5b^-/- murine model. Further study of individuals with decreased MUC5B production could provide unique mechanistic insights into airway mucus biology.

Interstitial lung disease in infancy and early childhood: a clinicopathological primer

Children's interstitial lung disease (chILD) encompasses a wide and heterogeneous spectrum of diseases substantially different from that of adults. Established classification systems divide chILD into conditions more prevalent in infancy and other conditions occurring at any age. This categorisation is based on a multidisciplinary approach including clinical, radiological, genetic and histological findings. The diagnostic evaluation may include lung biopsies if other diagnostic approaches failed to identify a precise chILD entity, or if severe or refractory respiratory distress of unknown cause is present. As the majority of children will be evaluated and diagnosed outside of specialist centres, this review summarises relevant clinical, genetic and histological findings of chILD to provide assistance in clinical assessment and rational diagnostics.

ILD of childhood is comparable by name only to lung disease in adults. A dedicated interdisciplinary team is required to achieve the best possible outcome. This review summarises the current clinicopathological criteria and associated genetic alterations.https://bit.ly/3mpxI3b

A Single-Institution Experience in the Use of Chest Radiographs for Hospitalized Children Labeled as Asthma Exacerbation

Background: Risks of diagnostic radiation have become more notable lately, particularly in young children with chronic medical conditions. This study reports on the cumulative radiation from chest radiographs in children with asthma. Its main purpose was to review our current practice and suggest minimizing the use of chest radiographs. Methods: The study was retrospective and conducted at a pediatric tertiary center. Eligibility criteria included children 2-15 y, admitted between January 2017 and December 2018 for asthma management. Results: Of the 643 children admitted as "asthma exacerbation," 243 [40% females; age (mean ± SD) 5.4±3.3 y] met the study criteria for inclusion. Ninety-two (38%) children had a temperature of 38.8±0.7°C on the day of admission. Antibiotics were prescribed for 148 (61%) children, mainly for presumed pneumonia. Chest radiographs were requested for 214 (88%) children, mainly on the day of admission. Only 38 (18%) chest radiographs showed focal/multifocal pneumonia justifying antibiotic use. Significant predictors for requesting chest radiographs were antibiotic use for presumed pneumonia, lower oxygen saturation at presentation, and a requested blood culture. The rate of chest radiographs per year was negatively related to the child's age; the younger the child the higher the rate (model coefficient -0.259, P < 0.001). For children < 5 y, the rate of chest radiographs was 1.39 ± 1.21/y and radiation dose 0.028 ± 0.025 mSv/y. The corresponding rates for children ≥5 y were 0.78 ± 0.72/y and 0.008 ± 0.007 mSv/y, respectively (P < 0.001). Conclusion: Chest radiographs were commonly requested for children with asthma, especially younger children. Prospective studies are necessary to measure the impact of this practice on the children's health.