A longitudinal sample study of twins looked at the impact of genetic factors in the persistence and early recovery of stuttering. Information from parents of the twins was collected at ages 2, 3, 4, and 7 years. This information was used to classify the twins for placement into recovered or persistent groups. Of the 12,892 children studied, 950 children had recovered and 135 were persistent stutterers.

The results of the study demonstrated that stuttering at age 2 was not predictive of later stuttering; however, stuttering at age 3 or 4 was predictive of continued stuttering. Concordance rates were higher for identical twins than fraternal twins, except for girls at age 3. At ages 3, 4, and 7 years, stuttering was highly heritable. Heritability for the recovered and persistent groups was also high but didn't differ from each other.

The authors concluded that genetics plays a high role in stuttering, and a shared environment has little effect in early childhood and for recovered and persistent groups of children by age 7.

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