ROBO2 and autism: The immunoreactive levels of PLXNA4 and ROBO2 were significantly reduced in the ACC of the autistic compared with that of the control brains, with a 53.0% reduction for PLXNA4 (t = -2.44, d.f. = 19, P < 0.05) and, a 53.4% reduction for ROBO2 (t = -2.14, d.f. = 19, P < 0.05) in the autism group relative to the control group (Figure 1B, C).