The expanding phenotype of MELAS caused by the m.3291T > C mutation in the MT-TL1 gene.

m.3291T > C mutation in the MT-TL1 gene has been infrequently encountered in association with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS), however remains poorly characterized from a clinical perspective. In the following report we describe in detail the phenotypic features, long term follow up (> 7 years) and management in a Caucasian family with MELAS due to the m.3291T > C mutation and review the literature on m.3291T > C mutation. The clinical phenotype in the proposita included overlapping features of MELAS, MERRF (Myoclonic epilepsy and ragged-red fiber syndrome), MNGIE (Mitochondrial neurogastrointestinal encephalopathy), KSS (Kearns-Sayre Syndrome) and CPEO (Chronic progressive external ophthalmoplegia).