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.

Genetic variants in children with chronic respiratory diseases.

Founder mutations and autosomal recessive (AR) disorders are common in the Arabian Peninsula due to frequent consanguineous marriages. As a result, the pulmonary service at Tawam Hospital (Al Ain, UAE) routinely requests genetic testing for children with persistent (unexplained) respiratory problems. The main purpose of this report was to underscore the usefulness of these tests. Ten children with severe respiratory diseases due to complex genetic findings are described here. Forty-one variants (six novel) were detected, averaging four per patient (range: 1-9). Seven (17%) variants were homozygous and 34 (83%) heterozygous; some variants were known to show monoallelic expression. Using binomial probability distribution, the fetal-risk for having AR disorder(s) as a function of the number of shared variants by a couple ranged from 0.25 (having one shared variant) to 0.9249 (having nine shared variants). In cultures where increased size of homozygous genomic segments is common, children often have multiple variants that could cause complex clinical phenotypes. Identifying pathogenic variants assists in clinical care, family counseling, and disease prevention through genetic screening.

Impact of high tidal volume ventilation on surfactant metabolism and lung injury in infant rats.

The poorly understood tolerance toward high tidal volume (VT) ventilation observed in critically ill children and age-equivalent animal models may be explained by surfactant homeostasis. The aim of our prospective animal study was to test whether high VT with adequate positive end-expiratory pressure (PEEP) is associated with surfactant de novo synthesis and secretion, leading to improved lung function, and whether extreme mechanical ventilation affects intracellular lamellar body formation and exocytosis. Rats (14 days old) were allocated to five groups: nonventilated controls, PEEP 5 cmH2O with VT of 8, 16, and 24 mL/kg, and PEEP 1 cmH2O with VT 24 mL/kg. Following 6 h of ventilation, lung function, surfactant proteins and phospholipids, and lamellar bodies were assessed by forced oscillation technique, quantitative real-time polymerase chain reaction, mass spectrometry, immunohistochemistry, and transmission electron microscopy. High VT (24 mL/kg) with PEEP of 5 cmH2O improved respiratory system mechanics and was not associated with lung injury, elevated surfactant protein expression, or surfactant phospholipid content. Extreme ventilation with VT 24 mL/kg and PEEP 1 cmH2O produced a mild inflammatory response and correlated with higher surfactant phospholipid concentrations in bronchoalveolar lavage fluid without affecting lamellar body count and morphology. Elevated phospholipid concentrations in the potentially most injurious strategy (VT 24 mL/kg, PEEP 1 cmH2O) need further evaluation and might reflect accumulation of biophysically inactive small aggregates. In conclusion, our data confirm the resilience of infant rats toward high VT-induced lung injury and challenge the relevance of surfactant synthesis, storage, and secretion as protective factors.

Lipid-Protein and Protein-Protein Interactions in the Pulmonary Surfactant System and Their Role in Lung Homeostasis.

Pulmonary surfactant is a lipid/protein complex synthesized by the alveolar epithelium and secreted into the airspaces, where it coats and protects the large respiratory air-liquid interface. Surfactant, assembled as a complex network of membranous structures, integrates elements in charge of reducing surface tension to a minimum along the breathing cycle, thus maintaining a large surface open to gas exchange and also protecting the lung and the body from the entrance of a myriad of potentially pathogenic entities. Different molecules in the surfactant establish a multivalent crosstalk with the epithelium, the immune system and the lung microbiota, constituting a crucial platform to sustain homeostasis, under health and disease. This review summarizes some of the most important molecules and interactions within lung surfactant and how multiple lipid-protein and protein-protein interactions contribute to the proper maintenance of an operative respiratory surface.

Neumonitis intersticial descamativa en el paciente pediátrico / Desquamative interstitial penumonitis in a pediatric patient

Introducción: la neumonitis intersticial descamativa es una entidad caracterizada en la clínica por mostrar tos, disnea, cianosis e hipercapnia, con un patrón restrictivo de las pruebas funcionales respiratorias, debido a la presencia de fibrosis pulmonar, cuya frecuencia es inusual en Pediatría. Presentación del caso: adolescente que fue remitida al Hospital Docente Pediátrico del Cerro por sospecha de dengue, al referir fiebre de 38 °C de 3 días de evolución, acompañada de dolores musculares en miembros inferiores, escalofríos y cefalea, por lo cual fue internada en la sala de misceláneas. Durante su evolución mostró dificultad respiratoria, tos seca, taquipnea, taquicardia y disminución del murmullo vesicular en la base del pulmón izquierdo. Se observó en la radiografía de tórax una opacidad en dicha zona y fue tratada con antibióticos. En etapa posterior se trasladó a la Unidad de Cuidados Intensivos por ocurrir un incremento de las lesiones pulmonares e insuficiencia respiratoria; por ello, se indicó ventilación mecánica, variedad presión controlada. Posteriormente se aisló en hemocultivo y secreciones bronquiales, Pseudomona Stutzeri, evento considerado como una sepsis asociada a cuidados sanitarios. Se planteó un distrés respiratorio del adulto en niños que no involucionó, y falleció en un cuadro de insuficiencia respiratoria a los 19 días de estadía. Conclusiones: esta paciente mostró síntomas y signos sugestivos de una infección pulmonar bacteriana de evolución tórpida. Los hallazgos necrópsicos describen la presencia de una bronconeumonía bacteriana como causa directa, y una neumonitis intersticial descamativa, como entidad básica del fallecimiento(AU)

Introduction: desquamative interstitial pneumonitis is a characterized condition in the clinical field since it shows cough, dysnea, cyanosis and hypercapnia, with a restrictive pattern of the functional respiratory tests due to the presence of pulmonary fibrosis that is unusual in pediatrics. Case presentation: a female adolescent was referred to the pediatric teaching hospital of Cerro on suspicion of dengue since she presented with 38 °C for three days, accompanied with muscle aches in lower limbs, chills and headache. She was admitted to a general ward. During her progression, she showed respiratory distress, unproductive cough, tachypnea, tachycardia and reduction of vesicular murmur in the left lung basis. The thoracic X ray showed opacity in the area and was treated with antibiotics. In a later phase, she was moced to the intensive care unit due to increase in pulmonary lesions and respiratory failure. She was also under mechanical ventilation with controlled pressure. Later, Pseudomona Stutzeri was isolated in blood culture and bronchial secretions, an event considered to be health care-associated sepsis. It was stated that this case was a respiratory distress of adult in a child that evolved and finally the adolescent died of respiratory failure 19 days after her hospitalization. Conclusions: this patient showed symptoms and signs suggestive of bacterial pulmonary infection of torpid progression. The necropsis finding describe the presence of bacterial bronchopneumonia as a direct cause and desquamative interstitial pneumonitis as the basic condition for death(AU)

Neumonitis intersticial descamativa en el paciente pediátrico / Desquamative interstitial penumonitis in a pediatric patient

Introducción: la neumonitis intersticial descamativa es una entidad caracterizada en la clínica por mostrar tos, disnea, cianosis e hipercapnia, con un patrón restrictivo de las pruebas funcionales respiratorias, debido a la presencia de fibrosis pulmonar, cuya frecuencia es inusual en Pediatría.Presentación del caso: adolescente que fue remitida al Hospital Docente Pediátrico del Cerro por sospecha de dengue, al referir fiebre de 38 °C de 3 días de evolución, acompañada de dolores musculares en miembros inferiores, escalofríos y cefalea, por lo cual fue internada en la sala de misceláneas. Durante su evolución mostró dificultad respiratoria, tos seca, taquipnea, taquicardia y disminución del murmullo vesicular en la base del pulmón izquierdo. Se observó en la radiografía de tórax una opacidad en dicha zona y fue tratada con antibióticos. En etapa posterior se trasladó a la Unidad de Cuidados Intensivos por ocurrir un incremento de las lesiones pulmonares e insuficiencia respiratoria; por ello, se indicó ventilación mecánica, variedad presión controlada. Posteriormente se aisló en hemocultivo y secreciones bronquiales, Pseudomona Stutzeri, evento considerado como una sepsis asociada a cuidados sanitarios. Se planteó un distrés respiratorio del adulto en niños que no involucionó, y falleció en un cuadro de insuficiencia respiratoria a los 19 días de estadía.Conclusiones: esta paciente mostró síntomas y signos sugestivos de una infección pulmonar bacteriana de evolución tórpida. Los hallazgos necrópsicos describen la presencia de una bronconeumonía bacteriana como causa directa, y una neumonitis intersticial descamativa, como entidad básica del fallecimiento(AU)

Analysis of the regulation of surfactant phosphatidylcholine metabolism using stable isotopes.

The pathways and mechanisms that regulate pulmonary surfactant synthesis, processing, secretion and catabolism have been extensively characterised using classical biochemical and analytical approaches. These have constructed a model, largely in experimental animals, for surfactant phospholipid metabolism in the alveolar epithelial cell whereby phospholipid synthesised on the endoplasmic reticulum is selectively transported to lamellar body storage vesicles, where it is subsequently processed before secretion into the alveolus. Surfactant phospholipid is a complex mixture of individual molecular species defined by the combination of esterified fatty acid groups and a comprehensive description of surfactant phospholipid metabolism requires consideration of the interactions between such molecular species. However, until recently, lipid analytical techniques have not kept pace with the considerable advances in understanding of the enzymology and molecular biology of surfactant metabolism. Refinements in electrospray ionisation mass spectrometry (ESI-MS) can now provide very sensitive platforms for the rapid characterisation of surfactant phospholipid composition in molecular detail. The combination of ESI-MS and administration of phospholipid substrates labelled with stable isotopes extends this analytical approach to the quantification of synthesis and turnover of individual molecular species of surfactant phospholipid. As this methodology does not involve radioactivity, it is ideally suited to application in clinical studies. This review will provide an overview of the metabolic processes that regulate the molecular specificity of surfactant phosphatidylcholine together with examples of how the application of stable isotope technologies in vivo has, for the first time, begun to explore regulation of the molecular specificity of surfactant synthesis in human subjects.

ABCA3 lung disease in an ex 27 week preterm infant responsive to systemic glucocorticosteroids.

We present a case of an infant born at almost 28 weeks gestation, found to be homozygous for a missense mutation of ABCA3, with diffuse lung disease that has continued throughout infancy. The patient's clinical course and chest imaging was highly suggestive of diffuse lung disease of infancy, and not of chronic lung disease of prematurity. The lung disease proved to be highly responsive to systemic corticosteroids. This is a case of ABCA3 lung disease that demonstrated improvement after systemic glucocorticosteroid administration.