Because the Drosophila melanogaster homolog of ROBO1 is involved in formation of neural connections between the left and right brain (Kidd et al., 1998) and because ROBO1 activity was reduced in 19 dyslexic members of the large Finnish family that had provided linkage to this region (Nopola-Hemmi et al., 2001), the authors hypothesized that dyslexia in rare families may be caused by partial haploinsufficiency of the gene. This evidence concerns the gene ROBO1 and dyslexia.