Contact

Karen Henry
Life Span Institute
785-864-0756

Twin study suggests language delay due more to nature than nurture

Mon, 07/21/2014

LAWRENCE — A study of 473 sets of twins followed since birth found that compared with single-born children, 47 percent of 24-month-old identical twins had language delay compared with 31 percent of nonidentical twins. Overall, twins had twice the rate of late language emergence of single-born children. None of the children had disabilities affecting language acquisition.

The results of the study were published in the June 2014 Journal of Speech, Language, and Hearing Research.

University of Kansas Distinguished Professor Mabel Rice, lead author, said that all of the language traits analyzed in the study—vocabulary, combining words and grammar—were significantly heritable with genes accounting for about 43 percent of the overall twins’ deficit.

The “twinning effect" — a lower level of language performance for twins than single-born children — was expected to be comparable for both kinds of twins, but was greater for identical twins, said Rice, strengthening the case for the heritability of language development.

“This finding disputes hypotheses that attribute delays in early language acquisition of twins to mothers whose attention is reduced due to the demands of caring for two toddlers,” Rice said. “This should reassure busy parents who worry about giving sufficient individual attention to each child.”

However, said Rice, prematurity and birth complications, more common in identical twins, could also affect their higher rates of language delay. A study of pregnancy and birth risks for late talking in twins is currently under way by the study authors.

Further, the study will continue at least until 2017 to continue to follow the twins through preschool and school years up to adolescence to answer the question of whether late-talking twins do catch up to their peers.

“Twin studies provide unique opportunities to study inherited and environmental contributions to language acquisition,” Rice said. “The outcomes inform our understanding of how these influences contribute to language acquisition in single-born children as well.”

Late language emergence means that a child’s language is below age and gender expectations in the number of words they speak and combining two or more words into sentences. In this study, 71 percent of 2-year-old twins were not combining words compared with 17 percent of single-born children.

While previous behavioral genetics studies of toddlers have largely focused on vocabulary, the researchers introduced an innovative measure of early grammatical ability on the correct use of the past tense and the “to be” and “to do” verbs. The measure was inspired by the Rice/Wexler Test of Early Grammar Impairment, developed in 2001 by Rice and Kenneth Wexler, Massachusetts Institute of Technology professor. It was the first test to detect the subtle but common language disorder, specific language impairment.

Rice’s collaborators in the international longitudinal project that began in 2002 are Professors Cate Taylor and Stephen Zubrick from the Telethon Kids Institute in Perth, Western Australia, and Professor Shelley Smith at the University of Nebraska Medical Center.

The study population is located in the vicinity of Perth, Western Australia, because it is demographically identical to Kansas City and several other U.S. Midwestern states. But in Australia health records are available, and the Western Australia Twin Registry is a unique resource for researchers since it is a record of all multiple births, Rice said.

The research group has followed the development of 1,000 sets of Western Australian twins from their first words. In 2012, the group was granted $2.8 million by the National Institute for Deafness and Other Communication Disorders for a fourth five-year-cycle that will enable researchers to continue to monitor the twins as they develop through adolescence. In addition to formal language tests, researchers have collected genetic and environmental data as well as assessments with the twins' siblings.

Other research by Rice: Researcher discovers genetic link to language disorder.



KU in the news
From Kansas Men's Basketball: Chalk Up 11: Kansas Men's Basketball's Comeback Claims Undisputed Crown More: http://kuathne.ws/1EiSAML #RockChalk

147 fall 2014 freshmen from 20 states recd Jayhawk Generations Scholarships. Be a part of the family. #BeAJayhawk http://t.co/MZ0CpCFlC1
Explore KU Seasons: Winter The crisp scrape of a shovel alerts your senses. Everything is different. Unexpected works of white powdery art are almost everywhere — some crafted by nature, others by whimsical students. Following a fresh snowfall, the University of Kansas’ campus takes on an almost magical majesty. And students flock out to explore the Hill under winter’s wonderful cloak, adding to their rich four-season experience as Jayhawks.


One of 34 U.S. public institutions in the prestigious Association of American Universities
26 prestigious Rhodes Scholars — more than all other Kansas colleges combined
Nearly $290 million in financial aid annually
46 nationally ranked graduate programs.
—U.S. News & World Report
Top 50 nationwide for size of library collection.
—ALA
23rd nationwide for service to veterans —"Best for Vets," Military Times