Interferon Stimulated Gene Expression Is a Biomarker for Primary Mitochondrial Disease

Objective Mitochondria are implicated in regulation of the innate immune response. We hypothesized that abnormalities in interferon signaling may contribute to pathophysiology in patients with primary mitochondrial disease (PMD). Methods Expression of interferon stimulated genes (ISGs) was measured by real‐time polymerase chain reaction (PCR) in whole blood samples from a cohort of patients with PMD. Results Upregulated ISG expression was observed in a high proportion (41/55, 75%) of patients with PMD on at least 1 occasion, most frequently IFI27 upregulation, seen in 50% of the samples. Some patients had extremely high IFI27 levels, similar to those seen in patients with primary interferonopathies. A statistically significant correlation was observed between elevated IFI27 gene expression and PMD, but not between IFI27 and secondary mitochondrial dysfunction, suggesting that ISG upregulation is a biomarker of PMD. In some patients with PMD, ISG abnormalities persisted on repeat measurement over several years, indicative of ongoing chronic inflammation. Subgroup analyses suggested common ISG signatures in patients with similar mitochondrial disease mechanisms and positive correlations with disease severity among patients with identical genetic diagnoses. Interpretation Dysregulated interferon signaling is frequently seen in patients with PMD suggesting that interferon dysregulation is a contributor to pathophysiology. This may indicate a role for repurposing of immunomodulatory therapies for the treatment of PMDs by targeting interferon signaling. ANN NEUROL 2024