Grhl3Cre-Rac1 mutants developed spina bifida at high penetrance (79.3%; Fig. 1C,E,F,I; Table 1), as described previously (Camerer et al., 2010), although a lower frequency of curly tail as the sole phenotype was also observed (13.8%; Fig. 1B,D; Table 1). Here, RAC1 is linked to spina bifida.