MT-TL1 and lactic acidosis: MT-TL1 is one of the most common pathogenic mitochondrial gene mutations, and is a genetic cause of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) (Goto et al., 1990; Chinnery et al., 2000; Majamaa et al., 1998; Uusimaa et al., 2007).