PTK7 and neural tube defect: Homozygosity for Vangl2Lp causes the severe NTD craniorachischisis, (33,34), while heterozygosity for Vangl2 can also cause craniorachischisis or SB when in combination with mutant alleles of other genes including Fzd2, Ptk7, Scrib and Sdc4 (35–37).