CYFIP1 and PTEN hamartoma tumor syndrome: In cases of CYFIP1 duplications, decreased PTEN protein levels could also affect wild-type PTEN. In the context of CYFIP1 deletion, as was observed for 1 of the 3 patients with PHTS and CNVs involving CYFIP1 in this study, increased levels of a mutant PTEN protein may result in dominant negative effects,53 inhibiting wild-type PTEN and hence exacerbating the condition.