EFNB1 and Spina bifida occulta: The first murine Eph and ephrin knockouts exhibited an open neural tube defect (ephrin-A5 null mice) [15], the second was a spina bifida occulta model (double heterozygous EphA2tmjrui/+ EphA4rb−2J/+) [22] and the most recent one (Efnb1-deficient embryo) was undefined as the phenotype was not assessed during the closure of primary neurulation [17].