For example, profiling of a mouse model with mutations in the Twinkle helicase and patient-derived transmitochondrial cybrids bearing the common m.3243A>G mtDNA mutation, associated with MELAS syndrome, identified new biomarkers such as fibroblast growth factor 21 (FGF21) and growth and differentiation factor 15 (GDF15) [52,53]. The gene discussed is FGF21; the disease is MELAS.