However there are multiple candidates for functional homologues, these candidates include 1) the WAGR syndrome PRRG4, which can re-localize Robo away from the cell surface in vitro [142], 2) Rab guanine nucleotide dissociation inhibitor (GDI), which regulates the levels of Robo1 on commissural axons in the chicken spinal cord by controlling its insertion into the growth cone membrane [143] and 3) two Nedd4-interacting proteins, Ndfip1 and Ndfip2, that localize Robo1 to endosomes [144]. This evidence concerns the gene ROBO1 and WAGR syndrome.