In a new study published in Genes & Development, researchers from the labs of Stefan Mundlos (Max Planck Institute for Molecular Genetics and Charité, Berlin) and Lila Allou (MRC Laboratory of Medical Sciences, London) demonstrate how different regulatory genetic elements coordinate the temporal activity of a key developmental gene. Their findings likely explain subtle differences seen in patients with congenital limb malformations, for which the underlying disease mechanisms often remain unknown.