Non-invasive evaluation of buccal respiratory chain enzyme dysfunction in mitochondrial disease: Comparison with studies in muscle biopsy

► Buccal mitochondrial respiratory complex (RC) activities can be reliably assessed. ► We assessed buccal RC levels in mitochondrial disease (MD) patients and controls. ► This MD cohort had marked deficiencies in either RC I or IV activities in muscle. ► Patient buccal data had a similar RC defect profile compared to previous muscle data. ► Correlation with muscle enzyme data supports a role for buccal tests in MD diagnosis.