VANGL2 and craniorachischisis: The Lp allele acts in a gene-dosage dependent manner such that heterozygous animals (Vangl2+/Lp) are viable but exhibit a looped tail, while homozygous embryos (Vangl2Lp/Lp, Lp mutant) die in utero due to craniorachischisis (Fig. 1A–C) (Smith and Stein, 1962).