Fragile X syndrome (FXS) is a monogenic cause of intellectual disability, developmental delay, and autism spectrum disorder (ASD), estimated to occur in 1 in 5,000 males and 1 in 4,000 to 1 in 8,000 females. It is caused by a CGG trinucleotide repeat expansion in the 5’ untranslated region of the fragile X messenger ribonucleoprotein 1 (FMR1) gene located at Xq27.3. A full mutation, greater than 200 CGG repeats, leads to silencing of the FMR1 gene and consequent loss of its product, the fragile X messenger ribonucleoprotein (FMRP). We generated FMR1 mutant common marmosets (Callithrix jacchus) using the CRISPR/Cas9 system and performed proteomic analysis of their neonatal forebrains to identify molecular changes associated with FMR1 deficiency. We analyzed samples from two wild-type (WT) and two FMR1 mutant marmosets.