The evidence from functional genetics is based on studies conducted on 4 to 5 candidate genes: KIAA0319, DCDC2, DYX1C1, KIAA0319L and, to some extent, ROBO1. Although these genes correspond to the strongest candidates, they only explain a small fraction of the genetic component underlying dyslexia and are likely to be a small subset of genes implicated in susceptibility to a complex, heterogeneous disorder like dyslexia. Here, DCDC2 is linked to dyslexia.