Using genetics to understand dyslexia.

This paper reviews what is currently known about the genetics of dyslexia and shows how genetic studies can help clarify which symptoms are primary and which are secondary in dyslexia. On the genetic side, current evidence supports the view that dyslexia is familial, substantially heritable, and heterogeneous in its genetic mechanisms. At least some forms of familial dyslexia appear to be autosomal dominant, with linkage studies supporting both a major locus on chromosome 15 and genetic heterogeneity. On the symptom side, current evidence supports the view that the primary symptom in dyslexia is a deficit in the phonological coding of written language. This primary symptom likewise appears to be heritable. Recent evidence suggests that the heritable precursor to this written language deficit is a spoken language deficit in the skill of phoneme segmentation and awareness.