Stroke-like episodes in familial mitochondrial encephalomyopathy: clinical and biochemical aspects

Subcutaneous microdialysis in mitochondrial cytopathy

We present the results of subcutaneous microdialysis, a new minimally invasive biochemical monitoring technique, in mitochondrial cytopathy. We studied 6 ambulatory patients with mitochondrial cytopathy and 6 controls without mitochondrial disease using a subcutaneous probe for continuous microdialysis, and obtained measurements of lactate, pyruvate, and glucose from samples gathered at 30-60 min intervals during the day and at 3-h intervals at night. The lactate:pyruvate ratio (LPR) was calculated and related to disease severity and metabolic stress. Microdialysis was well tolerated. Controls had stable lactate and pyruvate values in the normal range and a low LPR (average values between 0.0114 and 0.0145). Patients had widely fluctuating lactate and pyruvate values, a higher average LPR between 0.0187 and 0.0724, and marked diurnal variation, especially in the severely affected patients. Increases in the LPR coincided with metabolic stress in individual cases. We conclude that subcutaneous microdialysis is well tolerated and enables continuous metabolic monitoring of patients with mitochondrial cytopathy. It has particular potential for use in the identification of metabolic risk factors and may help to assess the impact of therapeutic regimens.

Clinical spectrum of the MELAS mutation in a large pedigree

INTRODUCTION

MELAS is most often due to an mentally transmitted A-G transition mutation of mitochondrial DNA (mtDNA) at position 3243. In this study we report on the clinical spectrum associated with the mutation in the largest family reported so far.

PATIENTS AND METHODS

In a family with three MELAS cases we identified 47 persons at risk for the mutation; sufficient data was available on 29. Mitochondrial disease was diagnosed in two of 9 deceased numbers (posthumous molecular analysis in one); 27 surviving family members underwent examination and 25 a molecular analysis of mt DNA from lymphoblasts. Then had a muscle biopsy and two were later autopsied.

RESULTS

All 26 cases investigated by molecular analysis showed the mutation at position 3243. The 18 symptomatic patients without stroke-like episodes had sensorineural hearing loss in 15 cases, diabetes in 6, nephropathy in 7, mild myopathy in 4, cardiomyopathy in 2, cerebellar disease in 4 and mental retardation in 2 cases. Eight carriers were asymptomatic. Autopsy showed > 80% mutant mt DNA in all tissues except blood (20%) examined in a MELAS patients, but < 20 mutant mt DNA in all tissues except lever (40%) and kidney (70%) in a patient with hepatopathy, renal failure and diabetes. Histologic and biochemical studies of muscle biopsy were often non-informative.

CONCLUSIONS

The mutation of mt DNA at position 3243 causes a multisystem disorder with a variable phenotype due to heteroplasmy. Most carriers are oligosymptomatic with hearing loss and a variety of neurological and internal medical symptoms. Diabetes, cardiomyopathy and renal disease, which is newly reported here for this mutation, are frequent. The blood test is a reliable screening tool in affected families, but is of prognostic value only combined with examination of other tissues.