Sensorineural hearing loss (HL) is one of the most frequent clinical features in patients with mitochondrial diseases caused by mitochondrial DNA (mtDNA) mutations, and hearing is impaired in over half of all cases with mitochondrial disorders. This study analyzed 373 patients with suspected hereditary HL using an extensive and rapid suspension-array screening system for 29 major mtDNA mutations, including the m.1555A4G homoplasmic mutation in the MT-RNR1 gene, which causes non-syndromic sensorineural HL and aminoglycoside-induced HL, and the m.3243A4G heteroplasmic mutation in the MT-TL1 gene. This method is rapid and suitable for large-scale screening because universal 96-well plates are available for use, and because an analysis of each plate can be completed within 1 h. This system detected five different mtDNA mutations in 24 of the 373 (6.4%) patients. The m.1555A4G and m.3243A4G mutations were detected in 11 (2.9%) and 9 (2.7%) patients, respectively. In addition, three mutations, that is, m.8348A4G in the MT-TK gene, m.11778G4A in the MT-ND4 gene and 15498G4A in the MT-CYB gene were detected in one patient for each. This screening system is useful for the genetic diagnosis and epidemiological study of both syndromic and non-syndromic HL.

The frequency of the HL patients carrying the mitochondrial haplogroup D4b was significantly higher than that of the controls (37/353 [10.5%] vs 31/480 [6.5%]; OR 1.70 [95% CI 1.03-2.79, p = 0.036]) and evidence for enhancement was found in subhaplogroup D4b2 (32/353 [9.1%] vs 24/480 [5%], OR 1.89 [95% CI 1.09-3.28, p = 0.021]).

Vocal cord abductor paralysis in MSA may cause sudden death, but when an otolaryngologist not familiar with this disease is asked for air way evaluation, it is possible to be diagnosed as no vocal cord paralysis because there is no an adductor disorder, so clinical course of MSA should be clarified more. In vocal cord midline fixation, it was expected that intervention by hypermyotony in the progress of Parkinsonism was a main factor, as was vocal cord abductor disorder due to a neurogenic change in the posterior cricoarytenoid muscle in MSA. The aggravation of dysphasia is an important index in judging the indication of tracheostomy.