Heritability of specific language impairment depends on diagnostic criteria

Heritability estimates for specific language impairment (SLI) have been inconsistent. Four twin studies reported heritability of 0.5 or more, but a recent report from the Twins Early Development Study found negligible genetic influence in 4-year-olds. We considered whether the method of ascertainment influenced results and found substantially higher heritability if SLI was defined in terms of referral to speech and language pathology services than if defined by language test scores. Further analysis showed that presence of speech difficulties played a major role in determining whether a child had contact with services. Childhood language disorders that are identified by population screening are likely to have a different phenotype and different etiology from clinically referred cases. Genetic studies are more likely to find high heritability if they focus on cases who have speech difficulties and who have been referred for intervention

Towards a typology of specific language impairment

Contains fulltext : 54578.pdf (publisher's version ) (Closed access)Background - The population of children with specific language impairments (SLI) is heterogeneous. The present study was conducted to examine this heterogeneity more closely, by identifying and describing subgroups within the population of children with SLI in the Netherlands. Method - A broad battery of language tests and language-related cognitive tests were administered to 147 six-year-old and 136 eight-year-old children with SLI. Results - Factor analyses revealed 4 factors indicating 4 distinctive linguistic domains for both age samples: 1) lexical-semantic abilities, 2) auditory conceptualization, 3) verbal sequential memory and 4) speech production. These empirical findings were further validated by the positive correlations found between the language factors and the judgments of teachers and speech therapists. Finally, a cluster analysis revealed 4 distinct clusters of SLI children for each sample with specific language profiles based on the 4 factors. Results were nearly the same for both age samples. Conclusions - The language problems that emerged from the two samples of children with SLI could be described as falling into four types. Based on these language types, four subgroups of children with SLI could be distinguished, each with a specific profile. Some subgroups had severe problems on one specific type of language problem; others had severe problems in more than one type of language problem when compared to the other subgroups of the same age sample. The different profiles may indicate that a more dynamic approach is needed in intervention, considering the presence of both compensating and restricting factors within each child with SLI.14 p