Family aggregation of language impairment in an isolated Chilean population from Robinson Crusoe Island.

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It has been reported that the inhabitants of the Chilean Robinson Crusoe Island have an increased frequency of specific language impairment (SLI) or developmental language disorder (DLD). To explore the familial aggregation of DLD in this community. We assessed the frequency of DLD amongst colonial children between the ages of 3 and 8;11 years (50 individuals from 45 nuclear families). Familial aggregation rates of language disorder were calculated by assessing all available first-degree relatives (n = 107, 77 parents, 25 siblings, five half-siblings) of the probands. We found that 71% of the child population performed significantly below expected in measures of phonological production or expressive and receptive morphology. The majority of these children presented with severe expressive and/or receptive language difficulties. One-quarter of language-disordered probands primarily had phonological difficulties. Family members of affected probands experienced a higher risk of language disorder than those of typically developing probands. This increased risk was apparent regardless of non-verbal IQ. The study substantiates the existence of a familial form of speech and language disorder on Robinson Crusoe Island. Furthermore, we find that the familiarity is stable regardless of non-verbal IQ, supporting the recent movement to reduce the importance of non-verbal IQ criterion in DLD diagnoses.