The Specificity of the Phenotype for Articulation Disorders
Previous research has shown that articulation disorders are heritable. The purpose of this study was to examine the specificity of the inherited phenotype of articulation disorders. The study compared the concordance of same-type articulation errors between monozygotic (MZ) and dizygotic (DZ) twins. The twins are participants in the Western Reserve Reading Project (WRRP). Participants included 24 same-sex twin pairs with a mean age of 7.14 years identified through parent report as having articulation difficulties. Concordance of error type was determined through review of conversational speech samples using liberal and conservative criteria. MZ twins had a concordance rate of 69% using conservative criteria and 94% using liberal criteria. DZ twins had a concordance rate of 43% using conservative criteria and 57% using liberal criteria. The findings suggest that individuals inherit a difficulty with specific speech sounds, not only a general predisposition to have articulation errors.