Early-phase ERK activation as a biomarker for metabolic status in fragile X syndrome.

Lack of production of the Fragile X Mental Retardation Protein (FMRP) leads to changes in dendritic morphology and resultant cognitive and behavioral manifestations characteristic of individuals with Fragile X syndrome (FXS). FMRP is an RNA-binding protein that is believed to regulate the translation of a large number (probably over 100) of other proteins, leading to a complex and variable set of symptoms in FXS. In a mouse model of FXS, we previously observed delayed initiation of synaptically localized protein synthesis in response to neurotransmitter stimulation, as compared to wild-type mice. We now likewise have observed delayed early-phase phosphorylation of extracellular-signal regulated kinase (ERK), a nodal point for cell signaling cascades, in both neurons and thymocytes of fmr-1 KO mice. We further report that early-phase kinetics of ERK activation in lymphocytes from human peripheral blood is delayed in a cohort of individuals with FXS, relative to normlal controls, suggesting a potential biomarker to measure metabolic status of disease for individuals with FXS.