Heritability of Specific Language Impairment and Nonspecific Language Impairment at Ages 4 and 6 Years Across Phenotypes of Speech, Language, and Nonverbal Cognition

Abstract

Purpose Early language and speech acquisition can be delayed in twin children, a twinning effect that diminishes between 4 and 6 years of age in a population-based sample. The purposes of this study were to examine how twinning effects influence the identification of children with language impairments at 4 and 6 years of age, comparing children with specific language impairment (SLI) and nonspecific language impairment (NLI); the likelihood that affectedness will be shared within monozygotic versus dizygotic twin pairs; and estimated levels of heritability for SLI and NLI. Twinning effects are predicted to result in elevated rates of language impairments in twins. Method The population-based twin sample included 1,354 children from 677 twin pairs, 214 monozygotic and 463 dizygotic, enrolled in a longitudinal study. Nine phenotypes from the same comprehensive direct behavioral assessment protocol were investigated at 4 and 6 years of age. Twinning effects were estimated for each phenotype at each age using structural equation models estimated via diagonally weighted least squares. Heritabilities were calculated for SLI and NLI. Results As predicted, the twinning effect increased the percentage of affected children in both groups across multiple language phenotypes, an effect that diminished with age yet was still not aligned to singleton age peers. Substantial heritability estimates replicated across language phenotypes and increased with age, even with the most lenient definition of affectedness, at −1 SD . Patterns of outcomes differed between SLI and NLI groups. Conclusions Nonverbal IQ is not on the same causal pathway as language impairments. Twinning effects on language acquisition affect classification of 4- and 6-year-old children as SLI and NLI, and heritability is most consistent in the SLI group. Clinical practice requires monitoring language acquisition of twins to avoid misdiagnosis when young or a missed diagnosis of language impairments at school entry.

Causal Pathways for Specific Language Impairment: Lessons From Studies of Twins

“…These heritability outcomes range from moderate to high, depending on the criterion used for low performance. Note that the range for the heritability outcomes is similar to those reported above ( Rice et al, 2020 ) using a criterion of a standard score of 85 as a cutoff, approximately the 15th percentile. Overall, the outcomes support the potential value of the GJ task as a clinical marker of SLI.…”

“…Direct assessments were carried out in appropriate rooms at a research building or, for families unable to travel, in mobile vans customized for the purpose of off-site data collection. Details of measurement can be found in previous reports (Rice et al, 2020(Rice et al, , 2014(Rice et al, , 2018.…”

“…Outcomes for SLI and Nonspecific Language Impairment of Twins at 4 and 6 Years: Dynamic Categorical Change Over Time A subsequent study (Rice et al, 2020) used the same sample as the previous study for the purpose of examining how twinning effects influence the identification of children with language impairments at 4 and 6 years of age, comparing children with SLI and children with nonspecific language impairment (NLI). The total number of twin pairs was 677 (214 MZ and 463 DZ).…”

Pedigree-Based Gene Mapping Supports Previous Loci and Reveals Novel Suggestive Loci in Specific Language Impairment

“…Other studies have used omnibus language measures in conjunction with additional language measures to assign affection status (Villanueva et al, 2010(Villanueva et al, , 2011(Villanueva et al, , 2008 or focused on performance on the NWR task, following up on the early results from the SLIC (Newbury et al, 2009;Whitehouse et al, 2011). A recent report showed high heritability of performance on omnibus language measures, in 6-year-old twins, using the TOLD-P:3, a more recent version of the TOLD measure used in this study (Newcomer & Hammill, 1997;Rice et al, 2020). In the context of previous studies, the study reported here contributes new information about omnibus language phenotypes, for the purpose of grouping participants as SLI.…”

“…Family aggregation and twin studies provide evidence that the language acquisition difficulties children with SLI experience are inherited (Bishop et al, 2006(Bishop et al, , 1995Bishop & Hayiou-Thomas, 2008;Rice et al, 1998Rice et al, , 2020Rice et al, , 2018Tallal et al, 2001). Twin studies of individuals with and without SLI have revealed strong heritability estimates for multiple speech and language phenotypes in dizygotic and monozygotic twins (Bishop & Hayiou-Thomas, 2008;Rice et al, 2020Rice et al, , 2018. Heritability estimates vary, ranging from .20 to .94, depending on the phenotype, age of children, and dimensions of language assessed.…”