Background Fragile X Syndrome (FXS) is the most common form of inherited autism and intellectual disability, with an estimated prevalence of 1 in 4000 males and 1 in 5-8000 females in Canada. Currently, there is no available cure for FXS. Evidence in the literature has implicated the dysregulation of protein synthesis, particularly the synthesis of synaptic proteins, as a key mechanism of FXS. A key signaling pathway for protein synthesis is the extracellular signal-regulated kinase (ERK) signalling pathway. There are conflicting reports in the literature on local synaptic protein synthesis levels of ERK and a lack of investigation on females. Methods and Results My experiments validated a reliable method of isolating synaptosomes, subcellular fractions of synaptic terminals, from mice brain tissue and a method of quantifying de novo protein synthesis levels, known as SUrface Sensing of Translation (SUnSET). My first research aim was to characterize protein synthesis levels and levels of ERK pathway proteins in the synaptosomes of an adult mouse model of FXS compared to the wildtype using SUnSET and western blot. We found prominent genotypic and sex differences in local protein synthesis at the synapse and in expression levels of ERK pathway proteins. My second aim was to characterize levels of synaptic proteins in the synaptosomes. My results demonstrated sex-differential results in the alterations to synaptic function, as indicated by synaptic protein expression levels, in the FXS model mice. Conclusion My study provided sex-different characterizations on local protein synthesis, ERK pathway proteins expression, and synaptic proteins in the FXS mouse model. Prominent sex differences were characterized, highlighting the need for future investigations to elucidate precise mechanisms and to account for sex differences in FXS pathophysiology.