FMR1 and fragile X syndrome: Fragile X mental retardation protein (FMRP), the protein lost in FXS, is best known as a translational repressor, and FMRP targets ∼1.4% of all mitochondrial annotated mRNAs (Suhl et al., 2014; Richter et al., 2015; Rath et al., 2021).