ABCA3 deficiency from birth to adulthood presenting as paediatric interstitial lung disease

ABC transporters involved in respiratory and cholestatic diseases: From rare to very rare monogenic diseases

ATP-binding cassette (ABC) transporters constitute a 49-member superfamily in humans. These proteins, most of them being transmembrane, allow the active transport of an important variety of substrates across biological membranes, using ATP hydrolysis as an energy source. For an important proportion of these ABC transporters, genetic variations of the loci encoding them have been correlated with rare genetic diseases, including cystic fibrosis and interstitial lung disease (variations in CFTR/ABCC7 and ABCA3) as well as cholestatic liver diseases (variations in ABCB4 and ABCB11). In this review, we first describe these ABC transporters and how their molecular dysfunction may lead to human diseases. Then, we propose a classification of the genetic variants according to their molecular defect (expression, traffic, function and/or stability), which may be considered as a general guideline for all ABC transporters' variants. Finally, we discuss recent progress in the field of targeted pharmacotherapy, which aim to correct specific molecular defects using small molecules. In conclusion, we are opening the path to treatment repurposing for diseases involving similar deficiencies in other ABC transporters.

Imaging of pulmonary fibrosis in children: A review, with proposed diagnostic criteria

Computed tomography (CT) imaging findings of pulmonary fibrosis are well established for adults and have been shown to correlate with prognosis and outcome. Recognition of fibrotic CT findings in children is more limited. With approved treatments for adult pulmonary fibrosis, it has become critical to define CT criteria for fibrosis in children, to identify patients in need of treatment and those eligible for clinical trials. Understanding how pediatric fibrosis compares with idiopathic pulmonary fibrosis and other causes of fibrosis in adults is increasingly important as these patients transition to adult care teams. Here, we review what is known regarding the features of pulmonary fibrosis in children compared with adults. Pulmonary fibrosis in children may be associated with genetic surfactant dysfunction disorders, autoimmune systemic disorders, and complications after radiation, chemotherapy, transplantation, and other exposures. Rather than a basal-predominant usual interstitial pneumonia pattern with honeycombing, pediatric fibrosis is primarily characterized by reticulation, traction bronchiectasis, architectural distortion, or cystic lucencies/abnormalities. Ground-glass opacities are more frequent in children with fibrotic interstitial lung disease than adults, and disease distribution appears more diffuse, without clearly defined axial or craniocaudal predominance. Following discussion and consensus amongst a panel of expert radiologists, pathologists and physicians, distinctive disease features were integrated to develop criteria for the first global Phase III trial in children with pulmonary fibrosis.

Neonatal and Infant Lung Disorders: Glossary, Practical Approach, and Diagnoses

A multitude of lung disorders ranging from congenital and genetic anomalies to iatrogenic complications can affect the neonate or the infant within the first year of life. Neonatal and infant chest imaging, predominantly by plain radiography and computed tomography, is frequently employed to aid in diagnosis and management; however, these disorders can be challenging to differentiate due to their broad-ranging, and frequently overlapping radiographic features. A systematic and practical approach to imaging interpretation which includes recognition of radiologic patterns, utilization of commonly accepted nomenclature and classification, as well as interpretation of imaging findings in conjunction with clinical history can not only assist radiologists to suggest the diagnosis, but also aid clinicians in management planning. The contents of this article were endorsed by the leadership of both the World Federation of Pediatric Imaging (WFPI), and the International Society of Pediatric Thoracic Imaging (ISPTI).

Combined Pulmonary Fibrosis and Emphysema: When Scylla and Charybdis Ally

Combined pulmonary fibrosis and emphysema (CPFE) is a recently recognized syndrome that, as its name indicates, involves the existence of both interstitial lung fibrosis and emphysema in one individual, and is often accompanied by pulmonary hypertension. This debilitating, progressive condition is most often encountered in males with an extensive smoking history, and is presented by dyspnea, preserved lung volumes, and contrastingly impaired gas exchange capacity. The diagnosis of the disease is based on computed tomography imaging, demonstrating the coexistence of emphysema and interstitial fibrosis in the lungs, which might be of various types and extents, in different areas of the lung and several relative positions to each other. CPFE bears high mortality and to date, specific and efficient treatment options do not exist. In this review, we will summarize current knowledge about the clinical attributes and manifestations of CPFE. Moreover, we will focus on pathophysiological and pathohistological lung phenomena and suspected etiological factors of this disease. Finally, since there is a paucity of preclinical research performed for this particular lung pathology, we will review existing animal studies and provide suggestions for the development of additional in vivo models of CPFE syndrome.

ABCA3

BACKGROUND

The majority of patients with childhood interstitial lung disease (chILD) caused by pathogenic variants in ATP binding cassette subfamily A member 3 (ABCA3) develop severe respiratory insufficiency within their first year of life and succumb to disease if not lung transplanted. This register-based cohort study reviews patients with ABCA3 lung disease who survived beyond the age of 1 year.

METHOD

Over a 21-year period, patients diagnosed as chILD due to ABCA3 deficiency were identified from the Kids Lung Register database. 44 patients survived beyond the first year of life and their long-term clinical course, oxygen supplementation and pulmonary function were reviewed. Chest CT and histopathology were scored blindly.

RESULTS

At the end of the observation period, median age was 6.3 years (IQR: 2.8-11.7) and 36/44 (82%) were still alive without transplantation. Patients who had never received supplemental oxygen therapy survived longer than those persistently required oxygen supplementation (9.7 (95% CI 6.7 to 27.7) vs 3.0 years (95% CI 1.5 to 5.0), p=0.0126). Interstitial lung disease was clearly progressive over time based on lung function (forced vital capacity % predicted absolute loss -1.1% /year) and on chest CT (increasing cystic lesions in those with repetitive imaging). Lung histology pattern were variable (chronic pneumonitis of infancy, non-specific interstitial pneumonia, and desquamative interstitial pneumonia). In 37/44 subjects, the ABCA3 sequence variants were missense variants, small insertions or deletions with in-silico tools predicting some residual ABCA3 transporter function.

CONCLUSION

The natural history of ABCA3-related interstitial lung disease progresses during childhood and adolescence. Disease-modifying treatments are desirable to delay such disease course.

The clinical course of interstitial lung disease in an adult patient with an ABCA3 homozygous complex allele under hydroxychloroquine and a review of the literature

The gene mutations responsible for ABCA3 protein deficiency are involved in respiratory distress of the newborn and much more rarely in adult interstitial lung diseases (ILD). An adult patient homozygous for a complex allele encompassing the p.Ala1027Pro likely pathogenic mutation and the p.Gly974Asp variation was followed for a late-onset and fibrotic ILD. The evolution was marked by progressive clinical and functional degradation despite corticosteroid pulses. The patient, who was first registered on the list for lung transplantation, was improved quickly and persistently for at least 6.5 years with hydroxychloroquine treatment, allowing removal from the transplant list.

Biologic characterization of ABCA3 variants in lung tissue from infants and children with ABCA3 deficiency

ABCA3 is a phospholipid transporter protein required for surfactant assembly in lamellar bodies of alveolar type II cells. Biallelic pathogenic ABCA3 variants cause severe neonatal respiratory distress syndrome or childhood interstitial lung disease. However, ABCA3 genotype alone does not explain the diversity in disease presentation, severity, and progression. Additionally, monoallelic ABCA3 variants have been reported in infants and children with ABCA3-deficient phenotypes. The effects of most ABCA3 variants identified in patients have not been characterized at the RNA level. ABCA3 allele-specific expression occurs in some cell types due to epigenetic regulation. We obtained lung tissue at transplant or autopsy from 16 infants and children with ABCA3 deficiency due to compound heterozygous ABCA3 variants for biologic characterization of the predicted effects of ABCA3 variants at the RNA level and determination of ABCA3 allele expression. We extracted DNA and RNA from frozen lung tissue and reverse-transcribed cDNA from mRNA. We performed Sanger sequencing to assess allele-specific expression by comparing the heights of variant nucleotide peaks in amplicons from genomic DNA and cDNA. We found similar genomic and cDNA variant nucleotide peak heights and no evidence of allele-specific expression among explant or autopsy samples with biallelic missense ABCA3 variants (n = 6). We observed allele-specific expression of missense alleles in trans with frameshift (n = 4) or nonsense (n = 1) variants, attributable to nonsense-mediated decay. The missense variant c.53 A > G;p.Gln18Arg, located near an exon-intron junction, encoded abnormal splicing with skipping of exon 4. Biologic characterization of ABCA3 variants can inform discovery of variant-specific disease mechanisms.

Case Report: Report of Two Cases of Interstitial Lung Disease Caused by Novel Compound Heterozygous Variants in the ABCA3 Gene

Interstitial lung disease (ILD) is a heterogeneous group of pulmonary disorders involving the lung interstitium and distal airways, also known as diffuse lung disease. The genetic defects resulting in alveolar surfactant protein dysfunction are a rare cause of ILD in pediatric patients. We report two unrelated pediatric patients with shortness of breath, dyspnea and hypoxemia, and the chest CT findings including patchy ground-glass opacity in both lung fields, suggestive of diffuse ILD. One patient was a full-term male infant who had shortness of breath a few hours after the birth, and then developed into severe respiratory distress syndrome (RDS). Whole exome sequencing revealed novel compound heterozygous variants in the ABCA3 gene (NM_001,089.3): paternally inherited c.4035+5G > A and c.668T > C (p.M223T), and maternally inherited c.1285+4A > C. The second patient was a 34-month-old boy with onset of chronic repeated cough and hypoxemia at 9 months of age. We unveiled novel compound heterozygous ABCA3 variants (c.704T > C, p.F235S; c.4037_4040del, p.T1346Nfs*15) in this patient. Surfactant protein dysfunction due to bi-allelic mutations in the ABCA3 gene was the cause of ILD in two patients. The novel mutations found in this study expanded the spectrum of known mutations in the ABCA3 gene.

Childhood Interstitial Lung Disease Masquerading as Post COVID-19 Respiratory Distress

Childhood interstitial lung diseases (chILD) are a set of illnesses affecting the bronchoalveolar spaces and the cellular compartment of the lungs. In the neonatal period, they are mainly classified under disorders of development, growth, surfactant dysfunction, and others of unknown causes distinctive in infancy. One of the most common causes is the deficiency of triphosphate binding cassette transporter A3 (ABCA3) protein. It activates impairment in the function of surfactants, resulting in respiratory distress in term infants, which is lethal in many cases and in some other cases leads to interstitial lung disease.

We herein present a case of a 14-month-old boy with a peculiar case of ABCA3 protein deficiency that was masked at birth with COVID-19 infection and then presented with shortness of breath and poor feeding at the age of three months. The child was treated with macrolides, steroids, and hydroxychloroquine, with which he survived beyond the age of one year.