Heritability of Language and Reading Measures in a Population Selected for Specific Language Impairment

Abstract:
Specific Language Impairment (SLI) is defined as a failure to develop language normally in absence of hearing, neurological or psychiatric explanations. SLI is characterized by poor performance on language, phonological and auditory temporal processing measures. Recently, twin studies have provided evidence that SLI may have a heritable component. Heritability is defined as the amount of variance under genetic control. The present study has used a different methodology to assess the heritable components of SLI by using a variance components method based on all members of the pedigree. Families were ascertained via a proband and at least one additional affected family member was required. The sample included 186 Americans comprised of 19 extended families with mixed ancestry. Heritability on a standardized comprehensive language test was estimated at 0.51 ± 0.12 (p < .001). Single word reading and single non-word reading were both found to be significant at 0.31 ± 0.13 (p< .01) and 0.40 ± 0.13 (p < .001) respectively. The fast sequences of the Tallal Repetition Test were also significantly heritable at 0.38 ± 0.15 (p < .001) for two-tone sequences and 0.47 ± 0.15 (p < .001) for three-tone sequences. These results demonstrate that several common research tools may prove useful in the search for SLI genes.