Hearing impairment & Fati...

A 54-year-old female patient was admitted, complaining of easy fatigability. She had been in good health until she first noticed hearing impairment at 32 years of age, which was slowly exacerbated over the subsequent twenty years, resulting in complete deafness. Although an elevated fasting blood glucose level was noted at the age of 40, she did not receive any treatment before visiting our hospital. She felt easy fatigability only but has never noticed any gait disturbance or muscle weakness in the extremities. She has never experienced any seizures, myoclonus, or stroke-like episodes. No family history of diabetes mellitus, muscle disorders or deafness. 

On admission, height was 150.5 cm, weight 32.5 kg, blood pressure 110/70 mmHg, and pulse 60 beats per minute, and regular. Neurological examination revealed normal intelligence. There was mild proximal muscular atrophy in her four limbs. Muscle strength was grade 4 on the manual muscle test. Sensitivity to vibration was decreased on bilateral medial malleolus. Deep tendon reflexes were diminished bilaterally. Chvostek's sign and Trousseau's sign were negative. Motor nerve conduction velocity in the median nerve was normal (54.5 m/sec). There were no findings of pigmentary retinopathy, cataract, blepharoptosis, or ophthalmoplegia. Simple diabetic retinopathy was observed during an ophthalmological examination. Audiometric studies showed complete sensorineural hearing loss in both ears. Her electrocardiogram was normal. Brain computed tomography revealed mild cerebral atrophy but no calcification in the basal ganglia. Laboratory data determined upon admission is shown in figure 1. Fasting blood glucose was 186 mg/dl, and haemoglobin A1Cwas 8.3%. Serum creatine kinase and lactate were normal. Urinalysis revealed glucosuria. Creatinine clearance was 61.7 ml/mi. Muscle biopsy specimens showed no specific abnormalities except for mild muscular atrophy. Subsequently, an A to G transition at nucleotide position3243 was examined in the mtDNA of the patient and her children.