Linking childhood interstitial lung disease to IARS-related disorder: clinical and preliminary functional studies in four new cases.

BACKGROUND

Biallelic mutations in aminoacyl-tRNA synthetase genes have been implicated in a variety of multisystem disorders. Nonetheless, the correlation between cytosolic IARS (which encodes isoleucyl-tRNA synthetase) and childhood interstitial lung disease (chILD) as well as pulmonary alveolar proteinosis (PAP) has yet to be established.

METHODS

We characterized the clinical features of four pediatric patients exhibiting progressive chILD/PAP alongside extrapulmonary manifestations (growth retardation, intellectual impairment, hypotonia, and liver disease). Whole exome sequencing was performed to confirm that biallelic IARS mutations are the etiological cause of the disease, and protein structural prediction was conducted for the identified pathogenic mutations via AlphaFold modeling. Periodic-Acid Schiff (PAS) and Oil-Red O (ORO) staining, along with western blotting and transmission electron microscopy of bronchoalveolar lavage fluid (BALF) and single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs) were used to characterize the disease phenotype and explore potential pathogenic mechanisms.

RESULTS

All four patients were confirmed to possess compound heterozygous IARS variants, inherited in trans from unaffected parents. Analysis of BALF revealed characteristic lipoprotein accumulation associated with PAP, evidenced by positive PAS and ORO staining. Additionally, surfactant proteins exhibited abnormal expression, accompanied by notable secondary lysosome formation and vacuolization within alveolar macrophages. scRNA-seq of PBMCs identified a specific depletion of CD14 + CD16+ intermediate monocytes and a transcriptional downregulation of phagosome/lysosome pathways in CD14 + classic monocytes. These findings suggest a potential intrinsic defect in the monocyte/macrophage lineage, potentially contributing to surfactant clearance dysfunction.

CONCLUSION

Our findings expand the phenotypic spectrum of IARS-related disorder by identifying chILD/PAP as a core and clinically significant pulmonary manifestation of biallelic IARS mutations. This study establishes IARS as a novel pathogenic gene for chILD/PAP and provides preliminary insights into the immune-related pathogenic mechanisms, highlighting the need for genetic screening of IARS variants in pediatric patients with unexplained respiratory failure and multisystem involvement.