Approximately 1% of diabetes is associated with a mitochondrial tRNA mutation at position 3,243, which was found in mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). Left ventricular hypertrophy (LVH) is often reported in MELAS (1).

We studied 12 type 2 diabetic patients with the mutation (DM-Mt3243). They were suspected of the mutation for maternally inherited diabetes or hearing impairment. The mutation was shown in the blood by a molecular test using ApaI. Echocardiography was performed in all of the DM-Mt3243 patients and compared with 184 ordinary type 2 diabetic patients. Between the two groups, age, sex, and diabetes duration were not different. Family history of diabetes in mothers was found in nine DM-Mt3243 patients (75%) and in 48 ordinary diabetic patients (26%). Hearing impairment was present in nine DM-Mt3243 patients. Blood pressures were not different. On echocardiograms, no patients with DM-Mt3243 showed wall motion abnormalities. Left ventricular internal dimensions were not different. DM-Mt3243 patients had greater left ventricular wall thickness (10.0 ± 1.5 vs. 9.0 ± 1.1 mm) and mass than ordinary diabetic patients (P < 0.002). LVH (>11 mm) was found in 4 DM-Mt3243 patients (33%) vs. 13 ordinary diabetic patients (7%) (P < 0.01). However, no individuals with DM-Mt3243 had marked LVH (>15 mm), such as hypertrophic cardiomyopathy (HCM). In pulsed Doppler of left ventricular inflow, DM-Mt3243 patients had longer deceleration time of E wave and greater A-to-E velocity ratios (1.24 ± 0.22 vs. 1.05 ± 0.21) than ordinary diabetic patients (P < 0.005).

Anan et al. (1) performed echocardiography in five MELAS patients and found LVH in two (40%). One patient had systolic dysfunction. In a follow-up study of six MELAS patients, an increase in left ventricular wall thickness was found in three patients, two of whom showed a decrease in systolic function. The 3,243 mutation would be a causative factor for LVH and may cause systolic dysfunction with progressive LVH. In marked LVH, abnormally increased mitochondria were shown. These abnormalities are considered a compensatory reaction to mitochondrial metabolic alterations.

In DM-Mt3243, six cases with HCM were reported, three of whom had systolic dysfunction (26). In such patients, much more abundant mutation was shown in myocardium than in blood (3). Abnormally increased mitochondria were also reported (5). LVH would be the feature of cardiac involvement in DM-Mt3243; however, there is no report to show prevalence and severity of LVH. Ueno and Shiotani (7) reported that 10 DM-Mt3243 patients had thicker left ventricular wall than 19 ordinary diabetic patients, but they did not show prevalence of LVH or the reasons why their patients had a molecular test. We showed that LVH was present in 33% of DM-Mt3243 patients, which is lower than the reported prevalence of MELAS (40%) (1). None of our DM-Mt3243 patients had marked LVH, such as HCM. Hence, LVH in DM-Mt3243 is less severe than in MELAS. Also, none of our DM-Mt3243 patients had systolic dysfunction. Because LVH in DM-Mt3243 is mild and systolic function is reported to correlate negatively with increased thickness in MELAS, systolic dysfunction would be uncommon. However, diastolic function was more severely impaired in DM-Mt3243 patients than in ordinary diabetic patients. Although diastolic dysfunction in DM-Mt3243 could be attributed to LVH, impaired mitochondrial ATP production may be contributing to diastolic dysfunction. Thus, DM-Mt3243 patients more often have LVH with diastolic dysfunction than ordinary diabetic patients. However, marked LVH, such as HCM, and systolic dysfunction are uncommon.

The authors would like to thank Masako Ohtomo of Tokyo Saiseikai Central Hospital for her secretarial assistance.

1
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Address correspondence to Yukihiko Momiyama, First Department of Internal Medicine, National Defense Medical College, 3-2 Namiki, Tokorozawa, Saitama 359-8513, Japan. E-mail: momiyama@me.ndmc.ac.jp.