Vangl-2 (formerly known as Ltap and Lpp1) has been identified as the causative gene in the loop-tail mouse [105, 268, 269]. Mutations in Celsr-1 cause craniorachischisis in the Crash mouse . The Dvl-1/Dvl-2, Dvl-2/Dvl-3, Dvl-2/Vangl-2, and Fzd-3/Fzd-6 double knockout mice also have severe NTD forms, mainly craniorachischisis and exencephaly [269, 271–273]. The Vangl-1 and Vangl-2 compound heterozygote exhibits craniorachischisis . The noncore PCP genes also exhibit severe NTD in their mouse mutants including Protein Tyrosine Kinase 7 (PTK7), Scribbled PCP protein, the gene responsible for the circle tail mouse phenotype, Scrib, and Dishevelled Binding Antagonist of Beta-Catenin 1 (Dact-1) [252, 270, 274–277]. All of these genes have been implicated in the PCP pathway. Failure of convergent extension results in an open neuraxis (the entire neural tube from midbrain to low spine remains exposed) and a shortened embryo, more commonly described as craniorachischisis.