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is a rare neurological condition that disrupts physical and linguistic development, affecting around one in 10,000 women and even fewer men. For decades, researchers assumed that people with the condition, many of whom lose speech during early childhood, were confined to a limited range of cognitive and linguistic abilities.

But in Wales, where many families are bilingual and speak both English and Welsh at home, showed that access to two languages can help the linguistic growth of someone with the speech-limiting developmental condition Rett syndrome.

Rett syndrome is caused by a in the MECP2 gene on the X chromosome in most cases. It usually manifests in early childhood, with most people showing typical development before a loss of skills at around 18 months of age. This process, known as “regression”, can lead to a loss of speech, mobility and the ability to use hands purposefully.

There are different variants of Rett syndrome. People with the may keep the ability to produce speech after regression, develop speech after regression, or develop speech without experiencing regression.

As well as movement and language difficulties, Rett syndrome can also cause scoliosis (curvature of the spine), seizures, irregular heart rhythm, digestive issues and breathing problems. The severity of varies widely from person to person.

To , many rely on such as body language, communication books, symbol charts, or high-tech devices to express themselves. These tools and techniques, known as augmentative and alternative communication, may replace or supplement speech.

While these strategies can be transformative, on communication methods for Rett syndrome have been based on research involving monolingual people. Until now, the possibility of bilingualism in people with Rett syndrome had not been formally explored.

Early researchers assumed that people with Rett syndrome would be limited to a cognitive ability of an 18-month-old, since this is the point where many experience a regression in skills. Recent research has started to show that this is not the case, with studies concluding that people with Rett syndrome show a .

Bilingualism

In Wales, where 17.8% of the population , bilingualism is a way of life for many families. Research has consistently shown that growing up with two languages benefits cognitive and linguistic development. For example, bilingual children often demonstrate skills compared to their monolingual peers.

But parents of children with developmental conditions, like Rett syndrome, are sometimes advised to . It often stems from a belief that bilingual exposure might hinder progress or . This belief persists despite growing evidence to the contrary.

Studies involving children with other developmental conditions, such as , have shown that bilingualism is achievable and does not negatively affect cognitive or linguistic abilities. Moreover, depriving a child from a bilingual family of one of their languages can have consequences, cutting them off from a vital part of their identity and community.

Prior to our research, there had been no studies focusing on bilingual development in Rett syndrome. Families had shared accounts indicating that many people with Rett syndrome are growing up in bilingual environments. Some research has explored parental perspectives on bilingualism in Rett syndrome, providing valuable insights into the .

Without research documenting language development itself, though, we had no evidence to show what is possible, or how to best support a bilingual person with Rett syndrome.

Our study focused on a teenage girl with the preserved speech variant of Rett syndrome. She had been exposed to both English and Welsh from birth. Using parental questionnaires, standardised tests and vocabulary diaries, we tracked her understanding and production of words in both languages over three years.

We found she could understand and produce words in both English and Welsh. Her vocabulary in both languages also expanded over time. This challenges long-held assumptions about the linguistic limitations of Rett syndrome. It also opens the door to new possibilities for supporting bilingualism in similar cases.

We are preparing to publish further findings that reinforce these results and explore how bilingualism can be supported in people with Rett syndrome. Future research will be crucial to developing evidence-based recommendations for bilingual language development. This may help to ensure that every person with Rett syndrome has the opportunity to reach their full potential.

Language is more than a tool for communication. It’s a gateway to connection, culture and identity. For people with Rett syndrome, the ability to engage with multiple languages can enrich their lives and strengthen their bonds with their families and communities. Our study is a small but important step towards understanding and supporting this potential.