Recent advances in understanding the genetics of reading and spelling disorder are reviewed and, based on theoretical models of reading development, different related phenotypes such as phonological and orthographic processing are examined. Family and twin studies show a moderate to high familiality and heritability. Segregation analyses suggest a major gene effect, with reduced penetrance in females, as well as a polygenic model. Linkage analyses and an association study have identified possible loci on chromosomes 6 and 15. These results suggest that reading and spelling disorder should be regarded as a complex disorder, strongly influenced by genetic factors. However, the role of environmental factors should also be considered as the clinical implications of the genetic findings in terms of aetiology and intervention still require far more exploration.
