The clock gene. Every cell in the human body keeps time. This intrinsic rhythm is roughly 24 hours long and driven by the molecular circadian clock: a transcriptional feedback loop that helps regulate sleep, metabolism, and hormone release. But what happens when these timekeepers stop working? In a recent study, we explored the role of BMAL1 (ARNTL), a core circadian regulator, in neurodevelopmental disorders. What we found surprised us: disruption of this central clock gene does not just affect sleep; it shapes the course of development itself.