FMR1 and fragile X syndrome: At the mechanistic level, our findings of mitochondrial dysfunction in the premutation may be explained by recent reports on fragile X syndrome’s models (contrary to the premutation, there is no detectable FMR1 gene or FMRP protein expression in males and reduced FMRP expression in females), in which FMRP was found to regulate mitochondrial mRNA expression and energy homeostasis (murine model), and energy metabolism and mitochondrial function (Drosophila model) [79,80].