TEFM is a mitochondrial transcription elongation factor that enhances the processivity of mitochondrial RNA polymerase (mtRNAP), enabling synthesis of long polycistronic transcripts from the mitochondrial genome 1. Mechanistically, TEFM functions as a sliding clamp that binds to transcribing mtRNAP and prevents formation of inhibitory RNA G-quadruplex structures at termination sites, thereby suppressing transcription termination and driving mtDNA replication 2. TEFM regulates transcription of genes encoding oxidative phosphorylation machinery components 3. Pathogenic TEFM variants cause childhood-onset neurological disease characterized by impaired mitochondrial respiratory chain function, mitochondrial myopathy, and neuromuscular transmission defects, with reduced levels of promoter-distal mitochondrial RNA transcripts 3. TEFM-associated congenital myasthenic syndrome represents a recently identified form of neuromuscular junction disease 4. Beyond mitochondrial disorders, TEFM dysregulation promotes malignancy in multiple cancer types; elevated TEFM expression in lung adenocarcinoma and endometrial carcinoma facilitates tumor progression through mitochondrial dysfunction-induced ROS production and inflammatory pathway activation 56. These findings identify TEFM as both a disease-associated gene and potential therapeutic target for both mitochondrial disorders and cancer.