The linguistic and metalinguistic abilities of monolingual and bilingual speakers with Prader–Willi syndrome

Although bilingualism is encouraged and promoted among typically developing (TD) individuals, some countries continue to recommend monolingualism for non-TD individuals. This common practice seems unfounded because existing research investigating the effects of bilingualism on non-TD individuals has not revealed a detrimental effect of bilingualism. In this study, we analyzed the linguistic and metalinguistic abilities of individuals with Prader–Willi syndrome (PWS). To manipulate grammaticality and semantics, a grammaticality judgment task was created and administered in Spanish to eight Spanish monolingual speakers and seven Spanish–Catalan bilingual speakers, all with PWS. Similar results were obtained for linguistic and metalinguistic abilities in both groups, even if the bilingual speakers were Catalan dominant. Thus, these results not only support previous research within the field in not identifying a negative effect of bilingualism but also emphasize the fact that bilingual speakers can mirror monolingual speakers even in their “weaker” language.