Abstract
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.
Highlights
Specific language impairment (SLI) is a developmental disorder that is diagnosed when a child’s language development is disproportionately poor relative to other skills for no apparent reason
Cases of SLI at 4 years are represented by the area of the set diagram, where low language does not intersect with low nonverbal
We started with the observation that results from HayiouThomas et al (2005) were inconsistent with previous studies, in that low and nonsignificant estimates of heritability for SLI were obtained in a sample of 4-year-olds
Summary
Specific language impairment (SLI) is a developmental disorder that is diagnosed when a child’s language development is disproportionately poor relative to other skills for no apparent reason. The child’s contact with speech and language pathology (SLP) services was not taken into account when identifying affected cases This raises the possibility that discrepancies between findings from twin studies may be explained by a ‘clinical concern’ hypothesis, which maintains that heritability is high only in those children who arouse parental concern and/or are referred for SLP services. This hypothesis fits with an analysis of preschool parental questionnaire data from TEDS, where heritability of early language delay was higher when the phenotype was defined in terms of parental concern or professional contact than when parental report of vocabulary size or language complexity were used (Bishop et al 2003). We used these data to evaluate the clinical concern hypothesis, by comparing heritability for SLI when the impairment was defined on the basis of psychometric test results at 4 years, as compared with when contact with SLP services by 7 years of age was the basis for diagnosis
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
