Genetic etiology in cases of recovered and persistent stuttering in an unselected, longitudinal sample of young twins
Dworzynski K., Remington A., Rijsdijk F., Howell P., Plomin R.
PURPOSE: The contribution of genetic factors in the persistence of and early recovery from stuttering was assessed. METHOD: Data from the Twins Early Development Study were employed. Parental reports regarding stuttering were collected at ages 2, 3, 4, and 7 years, and were used to classify speakers into recovered and persistent groups. Of 12,892 children with at least 2 ratings, 950 children had recovered and 135 persisted in their stutter. RESULTS: Logistic regressions showed that the rating at age 2 was not predictive of later stuttering, whereas ratings at ages 3 and 4 were. Concordance rates were consistently higher for monozygotic than for dizygotic twin pairs (with the exception of girls at age 3). At 3, 4, and 7 years, the liability to stuttering was highly heritable (h2 estimates of between .58 and .66). Heritability for the recovered and persistent groups was also high but did not differ from each other. CONCLUSION: Stuttering appears to be a disorder that has high heritability and little shared environment effect in early childhood and for recovered and persistent groups of children, by age 7. The clinical implications of the findings are discussed