Genetic influences on learning disabilities and speech and language disorders.

This paper is a comprehensive review of known examples of genetically influenced learning disabilities (LDs) and speech and language disorders (SLDs). The review is divided between 2 broad classes of studies: (a) those which begin with an LD or SLD phenotype that appears to be familial and attempt to learn more about the specifics of genetic transmission, if any; and (b) those which begin with a group of individuals, all of whom share a given documented genetic risk factor, to see if it leads to a specific LD or SLD. Included in the first category are familial dyslexia, stuttering, and other speech and language disorders. In the second category are included sex chromosome anomalies, treated PKU, and minor autosomal anomalies. Issues of definition, variability, and developmental changes in the cognitive phenotype are discussed throughout. The implications of this work for our understanding of cognitive development and its bases in brain development and genetics are also discussed.