MELAS, MIDD and Beyond: m.3243A>G MT-TL1 Mutation in Adult Patients

m.3243A>G MT-TL1 mutation is the most common mitochondrial DNA mutation that results in a wide spectrum of disorders in a maternally inherited pedigree. In adult patients, many present with symptoms and signs indistinguishable from acquired diseases and the correct diagnosis is often delayed after many years. Nevertheless, clues suggesting m.3243A>G usually exist early in the disease course but are only realized late. These hints, from the evolution of symptoms and signs, family background, investigation results, or a combination of these, enable the physician to make the correct diagnosis early, which is important for appropriate treatment and better patient care. As with other inheritable diseases, genetic counselling should be offered regarding the disease management, inheritance mode, recurrence risk, usefulness and limitations of genetic testing and reproductive options.