A JOURNAL OF NEUROLOGY LETTER TO THE EDITOR Reply: MFN2, a new gene responsible for mitochondrial DNA depletion

Sir, we recently showed in Brain that the MFN2 gene, typically responsible for autosomal dominant axonal Charcot–Marie–Tooth disease, is a novel gene associated with ‘mitochondrial DNA breakage ’ syndrome (Rouzier et al., 2012). We described a novel MFN2 heterozygous missense mutation in Tunisian patients who presented with optic atrophy beginning in early childhood, axonal neuropathy and mitochondrial myopathy in adult life with accumulation of mitochondrial DNA deletions in muscle. Renaldo et al. (2012) confirm that MFN2 is involved in mitochondrial DNA maintenance disorders. Indeed, they show that this gene is responsible for a severe phenotype in a child who presented a developmental delay with hypotonia and failure to thrive at the age of 6 months. Evolution was marked by the gradual appear-ance of ataxia, areflexia, abnormal movements and axonal sen-sorimotor neuropathy. At the age of 9 years, weight, height an