We report on a 3-year-old girl, from a 3-generation family with an FGFR3 Pro250Arg mutation, who in addition to craniosynostosis, had a laterality disorder and hepatoblastoma, following a pregnancy complicated by maternal insulin-dependent diabetes. The clinical features possibly result from the combined effects of the maternal diabetes and the familial FGFR3 mutation, thus representing a unique gene–environment interaction that may have implications for the understanding of the phenotypes described in this child.