Heterozygous dominant-negative and recessive hypomorphic mutations in FGFR1 have been implicated in causing dominant and recessive forms of Hartsfield syndrome, which is characterized by holoprosencephaly, ectrodactyly, cleft lip/palate, intellectual disability, and hypogonadotropic hypogonadism [73], and transgenic mice expressing a dominant-negative version of the FGFR1 demonstrate overt diabetes [1]. Here, FGFR1 is linked to diabetes mellitus.