FGFR3 and epilepsy: Other potentially relevant genes displaying the same expression trend were the heparan sulfate proteoglycan GPC2 (a marker of immature neurons [64, 72]), the helix–loop–helix transcription factor ID4 (a marker of postmitotic neurons [29]), and the signaling molecule FGFR3 that has been implicated in epilepsy [73].