Overall, there is accumulating evidence that altering the dosage of Cyfip1 in preclinical models leads to profound alterations in cellular and plasticity phenotypes, alongside mild behavioural phenotypes, many of which not only overlap with FXS and the Fmr1 KO model (Fig. 2), but also closely match the key clinical phenotypes of patients with chromosomal deletions (and duplications) of the CYFIP1-containing 15q11.2 interval. Here, FMR1 is linked to fragile X syndrome.