Different origin of auditory and phonological processing problems in children with language impairment: Evidence from a twin study

This study investigated the heritability of auditory processing impairment, as assessed by Tallal's Auditory Repetition Test (ART). The sample consist ed of 37 same-sex twin pairs who had previously been selected because one o r both twins met criteria For language impairment (LI) and 104 same-sex twi n pairs in the same age range (7 to 13 years) From the general population. These samples yielded 55 children who met criteria For LI, who were compare d with 76 children whose language was normal for their age (LN group). We r eplicated earlier work showing that group ii is impaired relative to group LN on ART. However, there was no evidence of a heritable influence on ART s cores: Correlations between twins and their co-twins were reasonably high f or both MZ and DZ twins, suggesting that performance is more influenced by shared environment than genetic Factors. Analyses of extreme scores gave a similar picture of nonsignificant group heritability. In contrast, a test o f phonological short-term memory, the Children's Nonword Repetition Test (C NRep), gave high estimates of group heritability. In general, CNRep was a b etter predictor of low language test scores than ART, but ART did make a si gnificant independent contribution in accounting For variance in a test of grammatical understanding.