Patients with monogenic immune dysregulation show improvement in childhood interstitial lung disease following targeted therapy -- a case series and single center approach

In recent years, a number of monogenic disorders have been described that are characterized by immune dysregulation. A subset of these ‘primary immune regulatory disorders’ can cause severe interstitial lung disease, often recognized in late childhood or adolescence. Patients presenting to pulmonary clinic may have long and complex medical histories but lack a unifying genetic diagnosis. It is crucial for pulmonologists to recognize features suggestive of multisystem immune dysregulation and to initiate genetic workup, since targeted therapies based on underlying genetics may halt or even reverese pulmonary disease progression. Through such an approach, our center has been able to diagnose and treat a cohort of patients with interstitial lung disease from gene defects that affect immune regulation. Here we present representative cases related to pathogenic mutations in three distinct pathways and summarize disease manifestations and treatment approaches. We conclude with a discussion of our perspective on the outstanding challenges for diagnosing and managing these complex life-threatening and chronic disorders.

A homozygous stop-gain variant in ARHGAP42 is associated with childhood interstitial lung disease, systemic hypertension, and immunological findings

ARHGAP42 encodes Rho GTPase activating protein 42 that belongs to a member of the GTPase Regulator Associated with Focal Adhesion Kinase (GRAF) family. ARHGAP42 is involved in blood pressure control by regulating vascular tone. Despite these findings, disorders of human variants in the coding part of ARHGAP42 have not been reported. Here, we describe an 8-year-old girl with childhood interstitial lung disease (chILD), systemic hypertension, and immunological findings who carries a homozygous stop-gain variant (c.469G>T, p.(Glu157Ter)) in the ARHGAP42 gene. The family history is notable for both parents with hypertension. Histopathological examination of the proband lung biopsy showed increased mural smooth muscle in small airways and alveolar septa, and concentric medial hypertrophy in pulmonary arteries. ARHGAP42 stop-gain variant in the proband leads to exon 5 skipping, and reduced ARHGAP42 levels, which was associated with enhanced RhoA and Cdc42 expression. This is the first report linking a homozygous stop-gain variant in ARHGAP42 with a chILD disorder, systemic hypertension, and immunological findings in human patient. Evidence of smooth muscle hypertrophy on lung biopsy and an increase in RhoA/ROCK signaling in patient cells suggests the potential mechanistic link between ARHGAP42 deficiency and the development of chILD disorder.

The common ABCA3E292V variant disrupts AT2 cell quality control and increases susceptibility to lung injury and aberrant remodeling

ATP binding cassette class A3 (ABCA3) is a lipid transporter that plays a critical role in pulmonary surfactant function. The substitution of valine for glutamic acid at codon 292 (E292V) produces a hypomorphic variant that accounts for a significant portion of ABCA3 mutations associated with lung disorders spanning from neonatal respiratory distress syndrome and childhood interstitial lung disease to diffuse parenchymal lung disease (DPLD) in adults including pulmonary fibrosis. The mechanisms by which this and similar ABCA3 mutations disrupt alveolar type 2 (AT2) cell homeostasis and cause DPLD are largely unclear. The present study, informed by a patient homozygous for the E292V variant, used an in vitro and a preclinical murine model to evaluate the mechanisms by which E292V expression promotes aberrant lung injury and parenchymal remodeling. Cell lines stably expressing EGFP-tagged ABCA3 isoforms show a functional deficiency of the ABCA3E292V variant as a lipid transporter. AT2 cells isolated from mice constitutively homozygous for ABCA3E292V demonstrate the presence of small electron-dense lamellar bodies, time dependent alterations in macroautophagy, and induction of apoptosis. These changes in AT2 cell homeostasis are accompanied by a spontaneous lung phenotype consisting of both age dependent inflammation and fibrillary collagen deposition in alveolar septae. Older ABCA3E292V mice exhibit increased vulnerability to exogenous lung injury by bleomycin. Collectively, these findings support the hypothesis that the ABCA3E292V variant is a susceptibility factor for lung injury through effects on surfactant deficiency and impaired AT2 autophagy.

ABCA 3 mutation associated childhood Interstitial Lung Disease (chILD) presenting as Combined Pulmonary Fibrosis and Emphysema in siblings.

Childhood interstitial lung diseases (chILD) are a rare presentation. We report case of siblings diagnosed with combined pulmonary fibrosis and emphysema (CPFE) attributable to ABCA 3 mutation. It highlights the progressive nature of the disease as it unfolds itself in both the siblings at around the same age. This is the second case of chILD with CPFE reported in literature and the first evidence of its occurrence in siblings adds to the novelty.