Mutations in FGF8 and FGFR1 are also relatively frequently observed in isolated HPE (>2% of cases), but they are also implicated in syndromes that include HPE (e.g., Kallman and Hartsfield syndromes) (Dubourg et al., 2016; Roessler et al., 2018a). Here, FGFR1 is linked to holoprosencephaly.