Volume 194 presents the most common clinical manifestations, providing an up-to-date summaries on the clinical presentations, diagnostic processes, genetic counseling and treatment options in mitochondrial diseases. Contents include specialist biochemical analyses and targeted molecular genetic testing, as well as first-line genome-wide sequencing to accelerate speed of diagnosis while avoiding time-consuming, expensive and invasive investigations. Establishing a genetic diagnosis allows patients with mitochondrial diseases to have reproductive options, all of which are covered within.