Progression of Cardiac Dysfunction in a Case of Mitochondrial Diabetes

Although there are some reports that have evaluated the correlation between mitochondrial tRNA(Leu) (UUR) mutation at position 3243 and cardiomyopathy, the degree of cardiac involvement in mitochondrial diabetes is still largely unknown. Here we report the case of a patient with mitochondrial diabetes who developed cardiac dysfunction, evaluated by echocardiography, along with worsening of glycemic control over a relatively short period, within a year. In April 1997, a 22-year-old Japanese man presented to a medical practice because of thirst, polyuria, and body weight loss of ∼8 kg over a few months. Because blood testing revealed a high plasma glucose level (23.6 mmol/l), and because urine was positive for ketone bodies, he was immediately admitted to the hospital. After initial therapy with insulin for 5 months, he was mainly treated with oral hypoglycemic agents. In July 1998, his glycemic control worsened and he presented to our hospital; insulin therapy was restarted. Because his maternal grandmother and paternal uncle had diabetes and he complained of hearing impairment, he was thought to have “mitochondrial diabetes.” After obtaining informed consent from the patient, mutation of the mitochondrial gene was analyzed. In leukocytes, A→G transition at the nucleotide pair 3243 of the mitochondrial gene was detected. Although he had no cardiac symptoms, to rule out cardiac involvement, further investigations (i.e., electrocardiography, chest X-ray, and echocardiography) were performed. No abnormal findings …