Persistent Lung Disease in Adults with NKX2.1 Mutation and Familial Neuroendocrine Cell Hyperplasia of Infancy

Genetic Disorders of Surfactant Metabolism

Genetic disorders affecting surfactant protein production and function can result in respiratory distress and severe respiratory failure in late-preterm and term neonates. Pathogenic variants in surfactant pulmonary-associated protein B (SFTPB) are typically loss-of-function and disrupt surfactant protein B (SP-B) production and surfactant function. Dominant variants in surfactant pulmonary-associated protein C (SFTPC) generally result in a toxic gain-of-function with disruption of surfactant protein C (SP-C) processing and trafficking in the alveolar epithelial type 2 cells. Adenosine triphosphate binding cassette transporter A3 (ABCA3) variants include loss-of-function or "null" variants in which no ABCA3 protein is made or missense variants that disrupt intracellular trafficking of ABCA3 or impair phospholipid transport. Pathogenic variants and deletions of the NK2 homeobox 1 gene (NKX2-1) result in haploinsufficiency and alter transcription of surfactant-associated genes as well as genes for brain and thyroid development. Diagnosis of these disorders requires a high index of clinical suspicion because presentations may vary between and within diseases. Prognosis is highly variable, ranging from requiring supportive care with improvement in respiratory status over time to severe disease with early mortality without lung transplantation. Neonatologists and pulmonologists alike should recognize early presentations of these rare genetic disorders of surfactant metabolism to identify and care for affected infants and to counsel families regarding prognosis, treatment options, recurrence risk, and risk assessment for other family members.

Childhood Interstitial Lung Diseases: Lessons Learned From 15-Year Observation at a Polish Referral Center

BACKGROUND

Childhood interstitial lung diseases (chILD) are rare, chronic lung diseases characterized by symptoms such as tachypnea, dyspnea, hypoxemia, crackles, and diffuse parenchymal abnormalities on chest imaging.

OBJECTIVE

To evaluate the etiologic spectrum, clinical presentation, management, and outcomes of chILD at a Polish referral center.

METHODS

We retrospectively reviewed data from patients (0-18 years) diagnosed with chILD, admitted to the Department of Pediatric Pulmonology and Allergy, Medical University of Warsaw, from June 2009 to February 2024, classified according to the chILD-EU categorization system.

RESULTS

A total of 275 patients (65.5% male) were included, with a median age at diagnosis of 13 months (range: 1-221). Persistent tachypnea of infancy (PTI)/neuroendocrine cell hyperplasia of infancy (NEHI) was the most common diagnosis (52.4%), followed by disorders related to systemic diseases (11.3%) and related to exposures (10.2%). 13.8% of diseases remained undefined. The predominant symptoms included crackles (81.5%), dyspnea (72.7%) and tachypnea (68.3%). All children underwent chest computed tomography. Bronchoscopy, genetic testing, and lung biopsy were performed in 46.2%, 34.9%, and 21.4% of cases, respectively. Most children (92.7%) received some form of treatment, including inhaled bronchodilators/steroids (68.8%), systemic steroids (26.5%), long-term macrolides (16.3%), and immunosuppressants (11.6%). Oxygen supplementation and nutritional support were required in 50.5% and 29.8% of patients, respectively. At a median follow-up of 31.5 months, 92.9% of patients achieved clinical improvement or stabilization, and 6.2% deteriorated, including seven deaths. The 5-year survival rate was 95.66%.

CONCLUSION

This study highlights the significant diversity within chILD, with PTI/NEHI being the most common condition.

Interstitial lung disease in the newborn

Although relatively rare, interstitial lung diseases may present with respiratory distress in the newborn period. Most commonly these include developmental and growth disorders, disorders of surfactant synthesis and homeostasis, pulmonary interstitial glycogenosis, and neuroendocrine cell hyperplasia of infancy. Although the diagnosis of these disorders is sometimes made based on clinical presentation and imaging, due to the significant overlap between disorders and phenotypic variability, lung biopsy or, increasingly genetic testing is needed for diagnosis. These diseases may result in significant morbidity and mortality. Effective medical treatment options are in some cases limited and/or invasive. The genetic basis for some of these disorders has been identified, and with increased utilization of exome and whole genome sequencing even before lung biopsy, further insights into their genetic etiologies should become available.

ABCA3 c.838C>T (p.Arg280Cys, R280C) and c.697C>T (p.Gln233Ter, Q233X, Q233*) as Causative Variants for RDS: A Family Case Study and Literature Review

Background: Respiratory distress syndrome (RDS) is the primary cause of respiratory failure in preterm infants, but it also affects 5-7% of term infants. Dysfunctions in pulmonary surfactant metabolism, resulting from mutations of the lung surfactant genes, are rare diseases, ranging from fatal neonatal RDS to interstitial lung disease, associated with increased morbidity and mortality. This study aims to clarify the clinical significance of ABCA3 variants found in a specific family case, as existing data in the literature are inconsistent. Material and Methods: A family case report was conducted; targeted panel genetic testing identified a variant of the SFTPB gene and two variants of ABCA3 genes. Comprehensive research involving a systematic review of PubMed, Google Scholar databases, and genome browsers was used to clarify the pathogenicity of the two ABCA3 variants found in the index patient. Advanced prediction tools were employed to assess the pathogenicity of the two ABCA3 variants, ensuring the validity and reliability of our findings. Results: The index case exhibited fatal neonatal RDS. Genetic testing revealed the presence of the SFTPB p.Val267Ile variant, which was not previously reported but is a benign variant based on family genetic testing and history. Additionally, two ABCA3 gene variants were identified: c.697C>T, not yet reported, and c.838C>T. These variants were found to affect ABCA3 protein function and were likely associated with neonatal RDS. Prediction tools and data from nine other cases in the literature supported this conclusion. Conclusions: Based on in silico predictors, an analysis of the presented family, and cases described in the literature, it is reasonable to consider reclassifying the two ABCA3 variants identified in the index case as pathogenic/pathogenic. Reclassification will improve genetic counseling accuracy and facilitate correct diagnosis.

Innovations in Childhood Interstitial and Diffuse Lung Disease

Children's interstitial and diffuse lung diseases (chILDs) are a heterogenous and diverse group of lung disorders presenting during childhood. Infants and children with chILD disorders present with respiratory signs and symptoms as well as diffuse lung imaging abnormalities. ChILD disorders are associated with significant health care resource utilization and high morbidity and mortality. The care of patients with chILD has been improved through multidisciplinary care, multicenter collaboration, and the establishment of patient research networks in the United Stated and abroad. This review details past and current innovations in the diagnosis and clinical care of children with chILD.

Genetics and Genomics of Pulmonary Fibrosis: Charting the Molecular Landscape and Shaping Precision Medicine

Recent genetic and genomic advancements have elucidated the complex etiology of idiopathic pulmonary fibrosis (IPF) and other progressive fibrotic interstitial lung diseases (ILDs), emphasizing the contribution of heritable factors. This state-of-the-art review synthesizes evidence on significant genetic contributors to pulmonary fibrosis (PF), including rare genetic variants and common SNPs. The MUC5B promoter variant is unusual, a common SNP that markedly elevates the risk of early and established PF. We address the utility of genetic variation in enhancing understanding of disease pathogenesis and clinical phenotypes, improving disease definitions, and informing prognosis and treatment response. Critical research gaps are highlighted, particularly the underrepresentation of non-European ancestries in PF genetic studies and the exploration of PF phenotypes beyond usual interstitial pneumonia/IPF. We discuss the role of telomere length, often critically short in PF, and its link to progression and mortality, underscoring the genetic complexity involving telomere biology genes (TERT, TERC) and others like SFTPC and MUC5B. In addition, we address the potential of gene-by-environment interactions to modulate disease manifestation, advocating for precision medicine in PF. Insights from gene expression profiling studies and multiomic analyses highlight the promise for understanding disease pathogenesis and offer new approaches to clinical care, therapeutic drug development, and biomarker discovery. Finally, we discuss the ethical, legal, and social implications of genomic research and therapies in PF, stressing the need for sound practices and informed clinical genetic discussions. Looking forward, we advocate for comprehensive genetic testing panels and polygenic risk scores to improve the management of PF and related ILDs across diverse populations.

Pulmonary neuroendocrine cells: crucial players in respiratory function and airway-nerve communication

Pulmonary neuroendocrine cells (PNECs) are unique airway epithelial cells that blend neuronal and endocrine functions, acting as key sensors in the lung. They respond to environmental stimuli like allergens by releasing neuropeptides and neurotransmitters. PNECs stand out as the only lung epithelial cells innervated by neurons, suggesting a significant role in airway-nerve communication via direct neural pathways and hormone release. Pathological conditions such as asthma are linked to increased PNECs counts and elevated calcitonin gene-related peptide (CGRP) production, which may affect neuroprotection and brain function. CGRP is also associated with neurodegenerative diseases, including Parkinson's and Alzheimer's, potentially due to its influence on inflammation and cholinergic activity. Despite their low numbers, PNECs are crucial for a wide range of functions, highlighting the importance of further research. Advances in technology for producing and culturing human PNECs enable the exploration of new mechanisms and cell-specific responses to targeted therapies for PNEC-focused treatments.

Pediatric Pulmonology 2022 year in review: Rare and diffuse lung disease

The field of rare and diffuse pediatric lung disease continues to evolve and expand rapidly as clinicians and researchers make advancements in the diagnosis and treatment of children's interstitial and diffuse lung disease, non-cystic fibrosis bronchiectasis, and primary ciliary dyskinesia. Papers published on these topics in Pediatric Pulmonology and other journals in 2022 describe newly recognized disorders, elucidate disease mechanisms and courses, explore potential biomarkers, and assess novel treatments. In this review, we will discuss these important advancements and place them in the context of existing literature.

Pediatric pulmonology 2021 year in review: Rare and diffuse lung disease

The field of rare and diffuse pediatric lung disease is experiencing rapid progress as diagnostic and therapeutic options continue to expand. In this annual review, we discuss manuscripts published in Pediatric Pulmonology in 2021 in (1) children's interstitial and diffuse lung disease, (2) congenital airway and lung malformations, and (3) noncystic fibrosis bronchiectasis including primary ciliary dyskinesia. These include case reports, descriptive cohorts, trials of therapies, animal model studies, and review articles. The results are put into the context of other literature in the field. Each furthers the field in important ways, while also highlighting the continued need for further studies.

Interstitial Lung Disease in Children: "Specific Conditions of Undefined Etiology" Becoming Clearer

BACKGROUND

Children's interstitial lung disease (chILD) is a rare group of pediatric lung diseases affecting the lung interstitium diffusely. In this work, we focused our attention on a specific infant group of chILD, also known as "specific conditions of undefined aetiology", including pulmonary interstitial glycogenosis (PIG) and neuroendocrine cell hyperplasia of infancy (NEHI).

METHODS

PubMed was searched to conduct this narrative review. We searched for articles in English using the following keywords: (1) neuroendocrine cell hyperplasia of infancy; (2) NEHI; (3) pulmonary interstitial glycogenosis; (4) PIG; (5) chILD.

RESULTS

An increasing interest and insight into these two conditions have been reported. The updated literature suggests that it is possible to look at these disorders as a continuum of diseases, rather than two different entities, since they share a pulmonary dysmaturity.

CONCLUSIONS

NEHI and PIG are featured by dysmaturity of airway development and consequent respiratory distress. Understanding the underlying pathogenic mechanisms would lead to identifying new targeted therapies to ameliorate the mortality and morbidity of these rare conditions.

A Rare Case Report of NEHI in a Preterm Infant with Review of the Literature

Background

Neuroendocrine cell hyperplasia of infancy (NEHI) is a rare respiratory disorder. During infancy, it typically presents with hypoxemia, tachypnea, and respiratory distress, and is commonly misdiagnosed as common childhood illnesses such as pneumonia, reactive airway disease, or bronchiolitis. Lack of awareness about this relatively new and rare disorder in primary care and acute care settings lead to delayed diagnosis and unnecessary use of antibiotics. Case Presentation. We present a case of a 7-month-old girl, born prematurely at 32 weeks with tachypnea and respiratory distress who was initially diagnosed with viral pneumonia, then upper respiratory infection, and finally with community-acquired bacterial pneumonia, while the child never had any fever or upper respiratory symptoms. Failure of outpatient treatment with oral antibiotic and bronchodilator, with the persistence of respiratory symptoms such as retractions, bilateral crackles, and hypoxemia led to hospitalization for intravenous antibiotics. Given persistent symptoms, further evaluation was performed, and she was diagnosed with NEHI based on characteristic chest CT findings.

Conclusions

Viral respiratory infections are the most frequent cause of respiratory illnesses in the first years of life. Primary care providers should be aware of less frequent causes of persistent respiratory symptoms in infancy like NEHI and other interstitial lung diseases in children. This may prevent unnecessary use of antibiotics and delayed diagnosis.

Childhood Interstitial Lung Disease: Imaging Guidelines and Recommendations

Childhood interstitial lung disease (ChILD) is an umbrella term encompassing a diverse group of diffuse lung diseases affecting infants and children. Although the timely and accurate diagnosis of ChILD is often challenging, it is optimally achieved through the multidisciplinary integration of imaging findings with clinical data, genetics, and potentially lung biopsy. This article reviews the definition and classification of ChILD; the role of imaging, pathology, and genetics in ChILD diagnosis; treatment options; and future goals. In addition, a practical approach to ChILD imaging based on the latest available research and the characteristic imaging appearance of ChILD entities are presented.

Surfactant protein disorders in childhood interstitial lung disease

Surfactant, which was first identified in the 1920s, is pivotal to lower the surface tension in alveoli of the lungs and helps to lower the work of breathing and prevents atelectasis. Surfactant proteins, such as surfactant protein B and surfactant protein C, contribute to function and stability of surfactant film. Additionally, adenosine triphosphate binding cassette 3 and thyroid transcription factor-1 are also integral for the normal structure and functioning of pulmonary surfactant. Through the study and improved understanding of surfactant over the decades, there is increasing interest into the study of childhood interstitial lung diseases (chILD) in the context of surfactant protein disorders. Surfactant protein deficiency syndrome (SPDS) is a group of rare diseases within the chILD group that is caused by genetic mutations of SFTPB, SFTPC, ABCA3 and TTF1 genes.Conclusion: This review article seeks to provide an overview of surfactant protein disorders in the context of chILD. What is Known: • Surfactant protein disorders are an extremely rare group of disorders caused by genetic mutations of SFTPB, SPTPC, ABCA3 and TTF1 genes. • Given its rarity, research is only beginning to unmask the pathophysiology, inheritance, spectrum of disease and its manifestations. What is New: • Diagnostic and treatment options continue to be explored and evolve in these conditions. • It is, therefore, imperative that we as paediatricians are abreast with current development in this field.

Genetic disorders of the surfactant system: focus on adult disease

Genes involved in the production of pulmonary surfactant are crucial for the development and maintenance of healthy lungs. Germline mutations in surfactant-related genes cause a spectrum of severe monogenic pulmonary diseases in patients of all ages. The majority of affected patients present at a very young age, however, a considerable portion of patients have adult-onset disease. Mutations in surfactant-related genes are present in up to 8% of adult patients with familial interstitial lung disease (ILD) and associate with the development of pulmonary fibrosis and lung cancer.High disease penetrance and variable expressivity underscore the potential value of genetic analysis for diagnostic purposes. However, scarce genotype-phenotype correlations and insufficient knowledge of mutation-specific pathogenic processes hamper the development of mutation-specific treatment options.This article describes the genetic origin of surfactant-related lung disease and presents spectra for gene, age, sex and pulmonary phenotype of adult carriers of germline mutations in surfactant-related genes.

Molecular Pathology of Well-Differentiated Pulmonary and Thymic Neuroendocrine Tumors: What Do Pathologists Need to Know?

Thoracic (pulmonary and thymic) neuroendocrine tumors are well-differentiated epithelial neuroendocrine neoplasms that are classified into typical and atypical carcinoid tumors based on mitotic index cut offs and presence or absence of necrosis. This classification scheme is of great prognostic value but designed for surgical specimens, only. Deep molecular characterization of thoracic neuroendocrine tumors highlighted their difference with neuroendocrine carcinomas. Neuroendocrine tumors of the lung are characterized by a low mutational burden, and a high prevalence of mutations in chromatin remodeling and histone modification-related genes, whereas mutations in genes frequently altered in neuroendocrine carcinomas are rare. Molecular profiling divided thymic neuroendocrine tumors into three clusters with distinct clinical outcomes and characterized by a different average of copy number instability. Moreover, integrated histopathological, molecular and clinical evidence supports the existence of a grey zone category between neuroendocrine tumors (carcinoid tumors) and neuroendocrine carcinomas. Indeed, cases with well differentiated morphology but mitotic/Ki-67 indexes close to neuroendocrine carcinomas have been increasingly recognized. These are characterized by specific molecular profiles and have an aggressive clinical behavior. Finally, thoracic neuroendocrine tumors may arise in the background of genetic susceptibility, being MEN1 syndrome the well-defined familial form. However, pathologists should be aware of rarer germline variants that are associated with the concurrence of neuroendocrine tumors of the lung or their precursors (such as DIPNECH) with other neoplasms, including but not limited to breast carcinomas. Therefore, genetic counseling for all young patients with thoracic neuroendocrine neoplasia and/or any patient with pathological evidence of neuroendocrine cell hyperplasia-to-neoplasia progression sequence or multifocal disease should be considered.

Pulmonary neuroendocrine cells: physiology, tissue homeostasis and disease

Mammalian lungs have the ability to recognize external environments by sensing different compounds in inhaled air. Pulmonary neuroendocrine cells (PNECs) are rare, multi-functional epithelial cells currently garnering attention as intrapulmonary sensors; PNECs can detect hypoxic conditions through chemoreception. Because PNEC overactivation has been reported in patients suffering from respiratory diseases – such as asthma, chronic obstructive pulmonary disease, bronchopulmonary dysplasia and other congenital diseases – an improved understanding of the fundamental characteristics of PNECs is becoming crucial in pulmonary biology and pathology. During the past decade, murine genetics and disease models revealed the involvement of PNECs in lung ventilation dynamics, mechanosensing and the type 2 immune responses. Single-cell RNA sequencing further unveiled heterogeneous gene expression profiles in the PNEC population and revealed that a small number of PNECs undergo reprogramming during regeneration. Aberrant large clusters of PNECs have been observed in neuroendocrine tumors, including small-cell lung cancer (SCLC). Modern innovation of imaging analyses has enabled the discovery of dynamic migratory behaviors of PNECs during airway development, perhaps relating to SCLC malignancy. This Review summarizes the findings from research on PNECs, along with novel knowledge about their function. In addition, it thoroughly addresses the relevant questions concerning the molecular pathology of pulmonary diseases and related therapeutic approaches.

Summary: This Review highlights the physiological relevance of pulmonary neuroendocrine cells, rare airway epithelial cells that form intrapulmonary sensory organs, abnormalities of which are associated with several pulmonary disorders, such as asthma and lung cancer.

Rare diffuse idiopathic pulmonary neuroendocrine cell hyperplasia: one case report and literature review

Rare diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH) was first diagnosed in the early 1950s, but was not fully recognized and named until 1992. Literatures reported that DIPNECH usual was multiple and diffuse bilateral nodules, rare patients demonstrate the single nodule or ground glass nodule (GGN). We diagnosed one patient because of intermittent dry cough at least one year, Chest computed tomography (CT) found a purity GGN (pGGN) in the anterior segment, right upper lung lobe, and bronchoscopy didn’t have any tumor in the bronchus in 2014. Continue follow-up 4 years, the nodule enlarged and became a mixed GGN (mGGN) in 2018 on chest CT. A diagnostics video-assisted thoracotomy with wedge resection in right upper lung lobe was performed. The pathology revealed that it was filled with neuroendocrine differentiation cells without penetration terminal bronchiole submucosal layer, immunohistochemical (IHC) staining were positive for CD-56, Cg-A, TTF, Syn and ki-67 (about 5%), leading to diagnosis of DIPNECH. A regular review of the chest CT showed no signs of tumor recurrence postoperative more than 1 year every 6 months, and we will continue follow-up. In conclusion, DIPNECH keeps stable evolution over several years, which is misdiagnosed and underdiagnosed usually. Patient who showed GGN on chest CT and had cough, dyspnea, wheezing, less frequently hemoptysis and so on, we should think of DIPNECH. Diagnosis depended on pathology and IHC staining, regular follow-up will lead to patient a long-term survival postoperative.

Interstitial lung disease in infancy

There is a wide differential diagnosis of early onset respiratory distress especially in term babies, and interstitial lung disease (chILD) is a rare but important consideration in this context. chILD manifesting immediately after birth is usually related to mutations in surfactant protein genes, or conditions related to the Congenital Acinar Dysplasia -Alveolar capillary dysplasia - Congenital Alveolar Dysplasia (CAD-ACD) spectrum. There is currently no specific treatment for these conditions, and management is supportive. Prognosis is very poor in most of these babies if onset is early, with relentless respiratory deterioration unless transplanted. Ideally, the diagnosis is made on genetic analysis, but this may be time-consuming and complex in CAD-ACD spectrum, so lung biopsy may be needed to avoid prolonged and futile treatment being instituted. Milder forms with prolonged survival have been reported. Early onset, less severe chILD is usually related to neuroendocrine cell hyperplasia of infancy (NEHI), pulmonary interstitial glycogenosis (PIG) and less severe disorders of surfactant proteins. PIG and NEHI are not specific entities, but are pulmonary dysmaturity syndromes, and there may be a number of underlying genetic and other cause. If the child is stable and thriving, many will not be subject to lung biopsy, and slow improvement and weaning of supplemental oxygen can be anticipated. Where possible, a precise genetic diagnosis should be made in early onset cHILD allow for genetic counselling. chILD survivors and their families have complex respiratory and other needs, and co-ordinated, multi-disciplinary support in the community is essential.

Persistent tachypnea of infancy: Follow up at school age

BACKGROUND

Persistent tachypnea of infancy (PTI) is a rare pediatric lung disease of unknown origin. The diagnosis can be made by clinical presentation and chest high resolution computed tomography after exclusion of other causes. Clinical courses beyond infancy have rarely been assessed.

METHODS

Patients included in the Kids Lung Register diagnosed with PTI as infants and now older than 5 years were identified. Initial presentation, extrapulmonary comorbidities, spirometry and clinical outcome were analyzed.

RESULTS

Thirty-five children older than 5 years with PTI diagnosed as infants were analyzed. At the age of 5 years, 74% of the patients were reported as asymptomatic and did not develope new symptoms during the observational period at school-age (mean, 3.9 years; range, 0.3-6.3). At the age of about 10 years, none of the symptomatic children had abnormal oxygen saturation during sleep or exercise anymore. Lung function tests and breathing frequency were within normal values throughout the entire observational period.

CONCLUSIONS

PTI is a pulmonary disease that can lead to respiratory insufficiency in infancy. As at school age most of the previously chronically affected children became asymptomatic and did not develop new symptoms. We conclude that the overall clinical course is favorable.

Recognizing genetic disease: A key aspect of pediatric pulmonary care

Advancement in technology has improved recognition of genetic etiologies of disease, which has impacted diagnosis and management of rare disease patients in the pediatric pulmonary clinic. This review provides an overview of genetic conditions that are likely to present with pulmonary features and require extensive care by the pediatric pulmonologist. Increased familiarity with these conditions allows for improved care of these patients by reducing time to diagnosis, tailoring management, and prompting further investigation into these disorders.

Interstitial lung diseases in children

Interstitial lung disease (ILD) in children (chILD) is a heterogeneous group of rare respiratory disorders that are mostly chronic and associated with high morbidity and mortality. The pathogenesis of the various chILD is complex and the diseases share common features of inflammatory and fibrotic changes of the lung parenchyma that impair gas exchanges. The etiologies of chILD are numerous. In this review, we chose to classify them as ILD related to exposure/environment insults, ILD related to systemic and immunological diseases, ILD related to primary lung parenchyma dysfunctions and ILD specific to infancy. A growing part of the etiologic spectrum of chILD is being attributed to molecular defects. Currently, the main genetic mutations associated with chILD are identified in the surfactant genes SFTPA1, SFTPA2, SFTPB, SFTPC, ABCA3 and NKX2-1. Other genetic contributors include mutations in MARS, CSF2RA and CSF2RB in pulmonary alveolar proteinosis, and mutations in TMEM173 and COPA in specific auto-inflammatory forms of chILD. However, only few genotype-phenotype correlations could be identified so far. Herein, information is provided about the clinical presentation and the diagnosis approach of chILD. Despite improvements in patient management, the therapeutic strategies are still relying mostly on corticosteroids although specific therapies are emerging. Larger longitudinal cohorts of patients are being gathered through ongoing international collaborations to improve disease knowledge and targeted therapies. Thus, it is expected that children with ILD will be able to reach the adulthood transition in a better condition.

Familial Interstitial Lung Disease

The interstitial lung diseases (ILDs) are a group of progressive disorders characterized by chronic inflammation and/or fibrosis in the lung. While some ILDs can be linked to specific environmental causes (i.e., asbestosis, silicosis), in many individuals, no culprit exposure can be identified; these patients are deemed to have "idiopathic interstitial pneumonia" (IIP). Family history is now recognized as the strongest risk factor for IIP, and IIP cases that run in families comprise a syndrome termed "familial interstitial pneumonia" (FIP). Mutations in more than 10 different genes have been implicated as responsible for disease in FIP families. Diverse ILD clinical phenotypes can be seen within a family, and available evidence suggests underlying genetic risk is the primary determinant of disease outcomes. Together, these FIP studies have provided unique insights into the pathobiology of ILDs, and brought focus on the unique issues that arise in the care of patients with FIP.

Abandoning developmental silos: what can paediatricians and adult interstitial lung disease physicians learn from each other?

PURPOSE OF REVIEW

Interstitial lung disease (ILD) consists of a large and heterogeneous group of disorders that are classified together because of similar clinical, radiographic, physiologic or pathologic manifestations. Overall, although there is overlap between adult and childhood ILD (chILD), there are many differences in disease causes and prevalences.

RECENT FINDINGS

In the last few years, our understanding of adult ILD pathobiology has improved substantially. This is particularly true for idiopathic pulmonary fibrosis, the most common of the idiopathic interstitial pneumonias, wherein recently developed guideline documents provide recommendations for the diagnosis and clinical management of patients. For chILD, similar guidelines are yet to be developed. However, complications and long-term pulmonary outcomes of paediatric disease are better appreciated, which make the implementation of a successful transition program from paediatric to adult care an urgent need. Similarly important is the development of guidelines on performance and interpretation of genetic testing in affected and unaffected relatives of familial cases and in children of adult-onset ILD patients. Lung transplantation appears to be as successful as in adult patients for end-stage disease. Paediatric pulmonologists should engage with the adult multidisciplinary teams and benefit from their much more extensive experience.

SUMMARY

Childhood and adult ILD share a number of aspects, which give children and adult ILD specialists exciting opportunities to collaborate and learn from each other. Such collaborative effort between child and adult ILD experts is crucial for successful future development in the field.

Ground-glass burden as a biomarker in neuroendocrine cell hyperplasia of infancy

BACKGROUND

Neuroendocrine cell hyperplasia of infancy (NEHI) is a rare pediatric interstitial lung disease (ILD). Distinct chest computed tomography (CT) define its radiographic appearance-specifically, ground-glass (GG) opacities most prominent in the right middle lobe (RML) and lingula. We sought to quantitatively validate this description and correlate radiologic findings with clinical presentation.

METHODS

Twenty-one children with NEHI were identified retrospectively, alongside 10 age-matched controls without lung disease. Clinical histories were reviewed for NEHI subjects. Semiautomated image analysis was used to measure lung volume and density. A patient-specific Hounsfield unit threshold defining GG was developed to quantify GG and assess its distribution in each subject.

RESULTS

NEHI subjects had more GG than controls (37.9 ± 11.3% vs 14.0 ± 2.7%, P < 0.0001). The proportion of GG in the RML and lingula was greater in NEHI patients compared to controls (1.43 ± 0.37 vs 0.45 ± 0.21, P < 0.0001). GG preferentially involved the RML and lingula in 20/21 NEHI subjects. There was more GG distribution in NEHI subjects who were prescribed continuous oxygen compared with those using only nocturnal oxygen (45.7 ± 8.9% vs 29.3 ± 6.1%, P = 0.003).

CONCLUSIONS

We confirm the previously reported finding that most patients with childhood ILD and a distinctive pattern of GG distribution on CT scan are likely to have NEHI. The amount of GG may be a biomarker for severity of respiratory disease.

Early onset children's interstitial lung diseases: Discrete entities or manifestations of pulmonary dysmaturity?

Interstitial lung diseases in children (chILD) are rare and diverse. The current classifications include a group of early onset chILD specific to infancy, namely neuro-endocrine cell hyperplasia of infancy (NEHI), pulmonary interstitial glycogenosis (PIG) and the alveolar capillary-congenital acinar dysplasia (ACD-CAD) spectrum, as well as alveolar growth disorders. NEHI and PIG cells are seen in the normal developing foetal lung. We hypothesise that these conditions are in fact overlapping manifestations of pulmonary dysmaturity, respectively of airway, mesenchymal and vascular elements, rather than discrete clinical conditions in their own right. Clinically, these present as respiratory distress in early life. Mild cases rightly never undergo lung biopsy, and for these the clinical description 'persistent tachypnoea of infancy' has been proposed. In terms of pathology, we reviewed current literature, which showed that NEHI cells decline with age, and are not specific to NEHI, which we confirmed by unpublished re-analysis of a second dataset. Furthermore, specific genetic disorders which affect pulmonary maturation lead to a histological picture indistinguishable from NEHI. PIG and ACD-CAD are also associated with pulmonary growth disorders, and manifestations of PIG and NEHI may be present in the same child. We conclude that, contrary to current classifications, NEHI, PIG, and ACD-CAD should be considered as overlapping manifestations of pulmonary dysmaturation, frequently associated with disorders of alveolar growth, rather than as separate conditions. Identification of one of these patterns should be the start, not the end of the diagnostic journey, and underlying in particular genetic causes should be sought.

Recent Developments in mRNA-Based Protein Supplementation Therapy to Target Lung Diseases

Protein supplementation therapy using in vitro-transcribed (IVT) mRNA for genetic diseases contains huge potential as a new class of therapy. From the early ages of synthetic mRNA discovery, a great number of studies showed the versatile use of IVT mRNA as a novel approach to supplement faulty or absent protein and also as a vaccine. Many modifications have been made to produce high expressions of mRNA causing less immunogenicity and more stability. Recent advancements in the in vivo lung delivery of mRNA complexed with various carriers encouraged the whole mRNA community to tackle various genetic lung diseases. This review gives a comprehensive overview of cells associated with various lung diseases and recent advancements in mRNA-based protein replacement therapy. This review also covers a brief summary of developments in mRNA modifications and nanocarriers toward clinical translation.

Building and Regenerating the Lung Cell by Cell

The unique architecture of the mammalian lung is required for adaptation to air breathing at birth and thereafter. Understanding the cellular and molecular mechanisms controlling its morphogenesis provides the framework for understanding the pathogenesis of acute and chronic lung diseases. Recent single-cell RNA sequencing data and high-resolution imaging identify the remarkable heterogeneity of pulmonary cell types and provides cell selective gene expression underlying lung development. We will address fundamental issues related to the diversity of pulmonary cells, to the formation and function of the mammalian lung, and will review recent advances regarding the cellular and molecular pathways involved in lung organogenesis. What cells form the lung in the early embryo? How are cell proliferation, migration, and differentiation regulated during lung morphogenesis? How do cells interact during lung formation and repair? How do signaling and transcriptional programs determine cell-cell interactions necessary for lung morphogenesis and function?

Consider the lung as a sensory organ: A tip from pulmonary neuroendocrine cells

While the lung is commonly known for its gas exchange function, it is exposed to signals in the inhaled air and responds to them by collaborating with other systems including immune cells and the neural circuit. This important aspect of lung physiology led us to consider the lung as a sensory organ. Among different cell types within the lung that mediate this role, several recent studies have renewed attention on pulmonary neuroendocrine cells (PNECs). PNECs are a rare, innervated airway epithelial cell type that accounts for <1% of the lung epithelium population. They are enriched at airway branch points. Classical in vitro studies have shown that PNECs can respond to an array of aerosol stimuli such as hypoxia, hypercapnia and nicotine. Recent in vivo evidence suggests an essential role of PNECs at neuroimmunomodulatory sites of action, releasing neuropeptides, neurotransmitters and facilitating asthmatic responses to allergen. In addition, evidence supports that PNECs can function both as progenitor cells and progenitor niches following airway epithelial injury. Increases in PNECs have been documented in a large array of chronic lung diseases. They are also the cells-of-origin for small cell lung cancer. A better understanding of the specificity of their responses to distinct insults, their impact on normal lung function and their roles in the pathogenesis of pulmonary ailments will be the next challenge toward designing therapeutics targeting the neuroendocrine system in lung.

Chronic interstitial lung diseases in children: diagnosis approaches

Introduction: Children interstitial lung disease (chILD) is a heterogeneous group of rare respiratory disorders characterized by inflammatory and fibrotic changes of the lung parenchyma. They include ILD related to exposure/environment insults, ILD related to systemic diseases processes, ILD related to primary lung parenchyma dysfunctions and ILD specific to infancy. Areas covered: This review provides an update on chILD pathophysiology and diagnosis approaches in immunocompetent children. It includes current information on genetic causes. Expert commentary: ChILD covers a large spectrum of entities with heterogeneous disease expression. Various classifications have been reported, but none of them seems completely satisfactory. Recently, progress in molecular genetics has allowed identifying some genetic contributors, with, so far, a lack of correlations between gene disorders and disease expression. Despite improvements in patient management, chILD prognosis is still burdened by significant morbidity and mortality. Ongoing international collaborations will allow gathering larger longitudinal cohorts of patients to improve disease knowledge and personalized care. The overall goal is to help the children with ILD to reach the adulthood transition in a better condition, and to structure genetic counseling for their family.

Growth trajectories and oxygen use in neuroendocrine cell hyperplasia of infancy

RATIONALE

Neuroendocrine cell hyperplasia of infancy (NEHI) typically presents in infancy with tachypnea, retractions, and hypoxemia. Some infants have failure to thrive, yet the frequency of this and other non-respiratory phenotypic features have not been delineated. While gradual improvement occurs, the clinical course is variable and the duration of supplemental oxygen requirement has not been defined.

OBJECTIVES

Our objective was to identify factors in NEHI that may drive differences in clinical course. We hypothesized that failure to thrive would be associated with greater duration of supplemental oxygen use.

METHODS

Children with NEHI were identified as a nested retrospective cohort within an ongoing observational prospective study. An electronic questionnaire evaluating health status was distributed to the parents/guardians. Clinical data were obtained via chart review and parent interview.

RESULTS

Of 42 children, 74% had a diagnosis of failure to thrive during their clinical course. Time to event analysis demonstrated that 50% discontinued daytime and nighttime oxygen at 32 and 87.5 months after initiation, respectively. Diagnosis of failure to thrive was associated with longer continuous oxygen supplementation, P = 0.03. Additional parental concerns identified through the electronic questionnaire included developmental delays, multiple hospitalizations, and delays in diagnosis.

CONCLUSIONS

NEHI is associated with substantial respiratory and extra-pulmonary morbidity. Failure to thrive may be associated with greater respiratory morbidity, though further studies are required to define this interaction. Determining the association of these comorbidities and respiratory course in NEHI may enable development of strategies to improve these modifiable factors and potentially pulmonary outcomes.

FOXP1 haploinsufficiency: Phenotypes beyond behavior and intellectual disability?

The forkhead box (FOX) transcription factors have roles in development, carcinogenesis, metabolism, and immunity. In humans FOXP1 mutations have been associated with language and speech defects, intellectual disability, autism spectrum disorder, facial dysmorphisms, and congenital anomalies of the kidney and urinary tract. In mice, Foxp1 plays critical roles in development of the spinal motor neurons, lymphocytes, cardiomyocytes, foregut, and skeleton. We hypothesized therefore that mutations of FOXP1 affect additional tissues in some humans. Supporting this hypothesis, we describe two individuals with novel variants of FOXP1 (NM_032682.5:c.975-2A>C and NM_032682.5:c.1574G>A) and additional features. One had a lung disease resembling neuroendocrine cell hyperplasia of infancy (NEHI), and the second had a skeletal disorder with undertubulation of the long bones and relapsing-remitting fevers associated with flushing and edema. Although attribution of these traits to mutation of FOXP1 requires ascertainment of additional patients, we hypothesize that the variable expression of these additional features might arise by means of stochastic developmental variation.