Pleuroparenchymal fibroelastosis in a monogenic mitochondrial DNA depletion syndrome.

BACKGROUND

Pleuroparenchymal fibroelastosis (PPFE) is a rare, most often idiopathic fibrotic lung disease with poor prognosis, mainly affecting adults. Biallelic pathogenic variants in the deoxyguanosine kinase gene (DGUOK) cause a mitochondrial DNA (mtDNA) depletion syndrome, predominantly affecting infants with severe hepatic and neurological disease. Neither detailed pulmonary manifestations nor a pulmonary-dominant phenotype has been reported.

METHODS

We describe nine patients with PPFE and DGUOK-associated mitochondriopathy. Clinical, radiological, histopathological, and genetic data were systematically collected from all patients. Functional studies, single-nucleus RNA sequencing (snRNAseq), immunofluorescence staining, transmission electron microscopy, respiratory chain enzyme activity assays and mtDNA recovery experiment were conducted on patient-derived fibroblasts, muscle or lung tissues. mtDNA content quantification was performed on whole genome sequencing data.

RESULTS

All patients (ages 5-36 years) carried biallelic pathogenic DGUOK variants, including an unreported intronic alteration in seven. All presented with progressive dyspnea, weight loss and some with pneumothoraces. Chest computed tomography and lung biopsies demonstrated features of PPFE. snRNAseq of lung tissue from four pediatric patients identified Aberrant Basaloid cells at the fibrotic edge, together with a transcriptional signature of nuclear DNA damage response. Ultrastructural analysis confirmed mitochondrial abnormalities in alveolar type 2 and Aberrant Basaloid cells.

CONCLUSION

This study provides evidence that mitochondrial dysfunction can contribute to early-onset PPFE independent of age, with a DNA damage response signature in aberrant epithelial cell populations previously described only in adult fibrotic lung disease. DGUOK deficiency and other hereditary mitochondrial disorders should be considered in children and young adults presenting with PPFE of unknown origin.