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Longitudinal Study of Language of Twins at Ages 9 and 14 Years: Twinning, Zygosity, and Heritability.

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Title: Longitudinal Study of Language of Twins at Ages 9 and 14 Years: Twinning, Zygosity, and Heritability.
Authors: Rice, Mabel L.1 mabel@ku.edu, Zubrick, Stephen R.2, Earnest, Kathleen Kelsey3, Hoffman, Lesa4
Source: Journal of Speech, Language & Hearing Research. Jun2026, Vol. 69 Issue 6, p2742-2756. 15p.
Subject Terms: *Language & languages, *Audiometry, *Longitudinal method, *Child development, *Vocabulary, *Language acquisition, *Cognition, Cross-sectional method, Research funding, Twins, Descriptive statistics, Maximum likelihood statistics, Data analysis software, Genetics, Phenotypes
Geographic Terms: Western Australia
Abstract: Purpose: This unprecedented longitudinal twin study focused on the arc of language acquisition from first words to adolescence, with data collection at 2, 4, and 6 years of age, reported in four previous studies and now new data at ages 9 and 14 years. Method: The method is a classic twin study design for estimating inherited versus environmental effects. The sample consisted of 1,188 children from 594 twin pairs, ascertained from birth records and followed for studying language and cognitive development. Here, we report language and nonverbal cognitive phenotypes at ages 9 and 14 years. Previous research reports from the sample at younger ages, as well as data from cross-sectional samples in other studies, supported the following generalizations: (a) Twinning effects persisted into adolescence for young children, such that twin children's language milestones were delayed relative to norms for singleton children; (b) twin type, that is, zygosity effects persisted although perhaps reduced with age; (c) gender also played a role for young children with advantages for girls relative to boys; and (d) heritability increased with age. Results: As in earlier studies, twins' standard scores for language were below the expected mean scores of 100 provided by test developers, 97 (SD = 14) at age 9 years and 95 (SD = 15) at age 14 years, although the gap relative to age peers is closing. Twin type effects, in which there was a slight disadvantage for monozygotic twins at age 4 years, disappeared at ages 9 and 14 years. Gender was significant at ages 9 and 14 years for vocabulary only but in the opposite direction than expected--with boys outperforming girls; however, this is consistent with singleton longitudinal findings from our lab. Models of heritability included adjustments for gender effects and other covariates. Heritability estimates at ages 9 and 14 years did not significantly differ. The final heritability estimates at age 14 years were .49, .71, and .85 for vocabulary, omnibus language, and nonverbal intelligence quotient (IQ), respectively, suggesting greater environmental effects for vocabulary relative to language and nonverbal IQ. Conclusion: The findings are consistent with previous reports, offering further empirical precision in estimation of the role of genetics in the transition from childhood to adolescence and further support for the need to consider genetics as well as the home environment in the lives of twin children. [ABSTRACT FROM AUTHOR]
Copyright of Journal of Speech, Language & Hearing Research is the property of American Speech-Language-Hearing Association and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Education Research Complete
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  Data: Longitudinal Study of Language of Twins at Ages 9 and 14 Years: Twinning, Zygosity, and Heritability.
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  Data: <searchLink fieldCode="AR" term="%22Rice%2C+Mabel+L%2E%22">Rice, Mabel L.</searchLink><relatesTo>1</relatesTo><i> mabel@ku.edu</i><br /><searchLink fieldCode="AR" term="%22Zubrick%2C+Stephen+R%2E%22">Zubrick, Stephen R.</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Earnest%2C+Kathleen+Kelsey%22">Earnest, Kathleen Kelsey</searchLink><relatesTo>3</relatesTo><br /><searchLink fieldCode="AR" term="%22Hoffman%2C+Lesa%22">Hoffman, Lesa</searchLink><relatesTo>4</relatesTo>
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Speech%2C+Language+%26+Hearing+Research%22">Journal of Speech, Language & Hearing Research</searchLink>. Jun2026, Vol. 69 Issue 6, p2742-2756. 15p.
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  Data: *<searchLink fieldCode="DE" term="%22Language+%26+languages%22">Language & languages</searchLink><br />*<searchLink fieldCode="DE" term="%22Audiometry%22">Audiometry</searchLink><br />*<searchLink fieldCode="DE" term="%22Longitudinal+method%22">Longitudinal method</searchLink><br />*<searchLink fieldCode="DE" term="%22Child+development%22">Child development</searchLink><br />*<searchLink fieldCode="DE" term="%22Vocabulary%22">Vocabulary</searchLink><br />*<searchLink fieldCode="DE" term="%22Language+acquisition%22">Language acquisition</searchLink><br />*<searchLink fieldCode="DE" term="%22Cognition%22">Cognition</searchLink><br /><searchLink fieldCode="DE" term="%22Cross-sectional+method%22">Cross-sectional method</searchLink><br /><searchLink fieldCode="DE" term="%22Research+funding%22">Research funding</searchLink><br /><searchLink fieldCode="DE" term="%22Twins%22">Twins</searchLink><br /><searchLink fieldCode="DE" term="%22Descriptive+statistics%22">Descriptive statistics</searchLink><br /><searchLink fieldCode="DE" term="%22Maximum+likelihood+statistics%22">Maximum likelihood statistics</searchLink><br /><searchLink fieldCode="DE" term="%22Data+analysis+software%22">Data analysis software</searchLink><br /><searchLink fieldCode="DE" term="%22Genetics%22">Genetics</searchLink><br /><searchLink fieldCode="DE" term="%22Phenotypes%22">Phenotypes</searchLink>
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  Data: <searchLink fieldCode="DE" term="%22Western+Australia%22">Western Australia</searchLink>
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  Label: Abstract
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  Data: Purpose: This unprecedented longitudinal twin study focused on the arc of language acquisition from first words to adolescence, with data collection at 2, 4, and 6 years of age, reported in four previous studies and now new data at ages 9 and 14 years. Method: The method is a classic twin study design for estimating inherited versus environmental effects. The sample consisted of 1,188 children from 594 twin pairs, ascertained from birth records and followed for studying language and cognitive development. Here, we report language and nonverbal cognitive phenotypes at ages 9 and 14 years. Previous research reports from the sample at younger ages, as well as data from cross-sectional samples in other studies, supported the following generalizations: (a) Twinning effects persisted into adolescence for young children, such that twin children's language milestones were delayed relative to norms for singleton children; (b) twin type, that is, zygosity effects persisted although perhaps reduced with age; (c) gender also played a role for young children with advantages for girls relative to boys; and (d) heritability increased with age. Results: As in earlier studies, twins' standard scores for language were below the expected mean scores of 100 provided by test developers, 97 (SD = 14) at age 9 years and 95 (SD = 15) at age 14 years, although the gap relative to age peers is closing. Twin type effects, in which there was a slight disadvantage for monozygotic twins at age 4 years, disappeared at ages 9 and 14 years. Gender was significant at ages 9 and 14 years for vocabulary only but in the opposite direction than expected--with boys outperforming girls; however, this is consistent with singleton longitudinal findings from our lab. Models of heritability included adjustments for gender effects and other covariates. Heritability estimates at ages 9 and 14 years did not significantly differ. The final heritability estimates at age 14 years were .49, .71, and .85 for vocabulary, omnibus language, and nonverbal intelligence quotient (IQ), respectively, suggesting greater environmental effects for vocabulary relative to language and nonverbal IQ. Conclusion: The findings are consistent with previous reports, offering further empirical precision in estimation of the role of genetics in the transition from childhood to adolescence and further support for the need to consider genetics as well as the home environment in the lives of twin children. [ABSTRACT FROM AUTHOR]
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  Data: <i>Copyright of Journal of Speech, Language & Hearing Research is the property of American Speech-Language-Hearing Association and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
PLink https://search.ebscohost.com/login.aspx?direct=true&site=eds-live&db=ehh&AN=194600821
RecordInfo BibRecord:
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      – Type: doi
        Value: 10.1044/2026_JSLHR-25-00673
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 15
        StartPage: 2742
    Subjects:
      – SubjectFull: Language & languages
        Type: general
      – SubjectFull: Audiometry
        Type: general
      – SubjectFull: Longitudinal method
        Type: general
      – SubjectFull: Child development
        Type: general
      – SubjectFull: Vocabulary
        Type: general
      – SubjectFull: Language acquisition
        Type: general
      – SubjectFull: Cognition
        Type: general
      – SubjectFull: Cross-sectional method
        Type: general
      – SubjectFull: Research funding
        Type: general
      – SubjectFull: Twins
        Type: general
      – SubjectFull: Descriptive statistics
        Type: general
      – SubjectFull: Maximum likelihood statistics
        Type: general
      – SubjectFull: Data analysis software
        Type: general
      – SubjectFull: Genetics
        Type: general
      – SubjectFull: Phenotypes
        Type: general
      – SubjectFull: Western Australia
        Type: general
    Titles:
      – TitleFull: Longitudinal Study of Language of Twins at Ages 9 and 14 Years: Twinning, Zygosity, and Heritability.
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          Name:
            NameFull: Rice, Mabel L.
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            NameFull: Zubrick, Stephen R.
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            NameFull: Earnest, Kathleen Kelsey
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            NameFull: Hoffman, Lesa
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              Text: Jun2026
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              Y: 2026
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