[Aspects of neuropathy in mitochondrial diseases]

The existence of neuropathy has been described in mitochondrial disorders such as MELAS, MERRF, Leigh's syndrome, the Kearns-Saye syndrome, myoneurogastro-intestinal encephalopathy and progressive external ophthalmoplegia and constitutes a basic component of the NARP (neuropathy, ataxia and retinosis pigmentosa). However, the general prevalence of the neuropathy and its characteristics within the mitochondrial encephalopathies is not well understood.

To characterize the neuropathy and try to establish a genotype-phenotype correlation.

Within study guidelines, we made a retrospective study of 27 patients, diagnosed as having mitochondrial disease, who had had neurophysiological studies (EMG-ENG). In those in whom neuropathy had been found we analysed the clinical, neurophysiological and genetic characteristics.

Neuropathy was present in 37% of the patients who had an average age of 13 years, ranging from 1 to 25 years. Syndromic diagnoses were: 7 encephalomyopathies, one MELAS, one MERRF and one NARP. Four of the patients were classified genetically. In all but two of the patients the neuropathy was asymptomatic. The biochemical alterations seen were: deficit of Complex 1 in 3 patients, of complex III in 3 patients, of complex IV in 2 and of pyruvate dehydrogenase in one patient. The type of neuropathy found was varied, with predominance of axonal-type motor neuropathy but no correlation with either biochemical defects or genetic diagnosis.

Neuropathy is a common finding in mitochondrial disorders and probably is under-diagnosed. The axonal form predominates. We have not been able to establish correlations between phenotypes and genotypes.