Abstract
The 3243 A to G mutation of the mitochondrial DNA (m.3243A>G) is responsible for mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS), and maternally inherited diabetes and deafness (MIDD). However, this mutation cannot be necessarily shown as typical phenotypes, and therefore it can cause isolated diabetes and hearing loss (HL).
A 48-year-old female, who had realized bilateral HL since her childhood, visited our department at the age of 18, received left tympanoplasty and was diagnosed as having left ossicular malformation. She returned to our department at the age of 33 because of the deterioration of her left HL. In her family history, maternal grandfather had HL, mother had diabetes, and maternal aunt had HL and diabetes, not suggesting of maternally inherited hereditary HL. After the second surgery, her left HL recovered. At the age of 44, m.3243A>G was detected in the patient as a result of an extensive screening for 29 major mitochondrial DNA mutation. At the same time, she realized the deterioration of her left HL, and the audiogram showed the increase of air-bone gaps at the lower frequencies tones with the slight elevation of bone conduction thresholds at the higher frequencies. She received an explanation that m.3243A>G can cause both the progression of HL and diabetes. She made a decision on using a hearing aid but not receiving third surgery. The patient was diagnosed as having early stage diabetes and started to receive dietary and exercise therapy. The m.3243A>G was a common mutation among the general population and can cause atypical features. Therefore, we should pay an attention for the existence of the mutation in a case whose family members have hearing loss and/or diabetes.
