Bilingualism in the preserved speech variant of Rett syndrome: A longitudinal case study.

Rett syndrome (RTT) is a neurodevelopmental condition affecting physical and linguistic development. To the authors' knowledge, there have been no studies published documenting bilingual linguistic abilities in an individual with RTT. Recent studies have found no evidence of a detrimental effect of bilingual exposure on language development in numerous other neurodevelopmental conditions. The aims of this study were to document bilingualism in RTT and to assess the development of language skills over time. A longitudinal, single-case study approach was taken for this research. The participant was a female adolescent with the preserved speech variant of Rett syndrome (PSV RTT), who had been exposed to both English and Welsh from birth. Data collection comprised administering parental questionnaires, documenting expressive vocabulary, and repeated administration of standardised English- and Welsh-medium tests at 18-month intervals. Repeated measures showed an improvement in linguistic and non-linguistic abilities between data points 1 and 2. There was a growth in English and Welsh expressive vocabulary in line with the participant's level of exposure to each language. Further increases in English and Welsh vocabulary comprehension were seen at the third data point after changes in the amount and mode of language exposure received. This study is the first to document bilingualism in RTT, including the development of receptive and expressive abilities in both languages over time. This study found no evidence of a detrimental effect of bilingualism in this individual and highlights the need for further research into bilingualism in RTT.