From neural tube patterning to limb development, Hh signalling exerts precise control over cellular processes [150]—evidenced by Shh‐null mice exhibiting characteristic distal limb truncations [151] and neural tube defects [152] that mirror human holoprosencephaly (HPE) with its concomitant craniofacial and skeletal abnormalities [153, 154]. The gene discussed is SHH; the disease is holoprosencephaly.