SHH and holoprosencephaly: TTBK2 is a serine/threonine kinase with a highly conserved kinase domain at its N‐terminal region.[42] Previous knockout studies have shown that TTBK2 is essential for cilliogenesis and Sonic hedgehog (Shh) signaling—a pathway crucial for embryogenesis, resulting in holoprosencephaly, abnormal neural tube and limb development, and embryonic lethality after Ttbk2 knockout.