Mitochondrial tRNAThr 15891C>G mutation was not associated with Leber's hereditary optic neuropathy in Han Chinese patients

ENT characteristics and therapeutic results in multisystemic disorders of mitochondrial encephalomyopathy

Here we report the evaluation of the frequency of subjective and objective otolaryngologic findings and therapeutic results in 32 patients with mitochondrial encephalomyopathy (MEM) from September 2001 to June 2021. Our analysis included studying the patients’ family histories, the clinical manifestations of MEM, and the therapeutic effects of treatments. The patients’ ages ranged from 2 to 77 years, with a median age of 12.3 years. We found that MEM ENT symptoms were characterized by hearing loss, dysphagia, and facial weakness. Most cases of sensorineural hearing loss were bilateral symmetrical progressive or sudden deafness since adolescence, which were often underestimated. Associated neuromuscular symptoms required mtDNA testing. Dysphagia and facial weakness occurred preferentially in middle-aged patients, and muscle biopsies were advised. Distortion product otoacoustic emissions and auditory brainstem responsetesting were more sensitive and reliable than pure tone averages for objective monitoring of pathogenesis. Administration of the mitochondrial synthase complex benefited patients with acute episodes. If patients did not fully recover and exhibitedresidual language deficits, hearing aids or cochlear implants were recommended. Counsel was given regarding synthetical treatments for facial weakness, endoscopic circopharyngealmyotomy for dysphagia, and surgical correction of ptosis. This study demonstrates that increased awareness of these symptoms is important to address appropriate interventions and avoid complications such as ablepsia, aphasia, social isolation, malnutrition, aspiration pneumonia, and heart failure in the setting of MEM.

The roles of mitochondrial tRNA mutations in non-dystrophic myotonias

According a recent report by Heidari et al., a mutational screening for candidate pathogenic mitochondrial tRNA (mt-tRNA) mutations were performed in 45 Iranian patients with non-dystrophic myotonia (NDM) and 70 control subjects. Through PCR amplification and direct sequence analysis, nine mt-tRNA mutations were identified: tRNA^Met T4454C, tRNA^Trp A5568G, tRNA^Cys T5794C, tRNA^Arg A10438T and T10462C, tRNA^Leu(CUN) A12308G, tRNA^Thr A15907G, A15924G and G15928A. However, through the database searches and phylogenetic conservation analysis, we noticed that the tRNA^Thr A15924G, G15928A and tRNA^Leu(CUN) A12308G mutations should be classified 'pathogenic'. Thus, the roles of mt-tRNA mutations in clinical expression of NDM needed to be further experimentally addressed.