Talking genetics with Robinson Crusoe
MRC-funded researcher Dianne Newbury won our international collaboration competition last year for a poster describing her work with researchers in Chile on speech and language development. When we heard that the story involved a mysterious predominance of language problems on the island that inspired Robinson Crusoe, we invited her to write about it.
Our story begins on a small island 400 miles off the coast of Chile in the Pacific Ocean. Robinson Crusoe Island is named after Alexander Selkirk, the Scottish sailor who was marooned on the island for four years in the 1700s and was reportedly the inspiration for Daniel Defoe’s famous novel.
The island is quiet, the climate warm and the vistas unique, making it an idyllic holiday location. It has a population of less than 1,000 individuals, most of whom live in the island’s only town, San Juan Bautista.
It is here that my colleague Prof Pia Villanueva found herself on a diving holiday in 1999. A speech and language pathologist at University of Chile, Pia was passing time with the locals while she prepared for a dive when an islander asked if he could get her opinion about his child who was slow to speak.
This in itself is not unusual, many children are slow to talk or have problems with some aspect of speech or language, but they usually grow out of it. In the UK, it is estimated that one in ten children require support for language difficulties.
The child in question’s development was normal in all areas except for a problem with producing speech and understanding language. Again, this is not uncommon; this is often described as Specific Language Impairment (SLI) and it is estimated that 5 per cent of children in the UK (and a similar number in mainland Chile) are affected.
The parents told Pia that the child’s brother also struggled with language, as did some other close relatives. This, again, is not unexpected – having a close family member affected by SLI increases your risk of language problems by about 50 per cent.
But what was striking in this particular case is the extent of the problem. Not only did this family report language problems but so did their neighbours, friends and colleagues throughout the community. Pia and her colleagues returned to the island to test the language skills of all children aged between three and nine, and found that two-thirds of the island’s children have impaired language development.
So what’s the cause? Everyone on the island speaks Chilean Spanish, the children attend the same school — which follows the same educational system and curriculum as mainland Chile — and the diet and environment of the islanders is not unusual. There was one only thing that Pia and her colleagues could find that distinguished the children with SLI — and that was their family history.
It turns out that our story actually began in 1876, when Robinson Crusoe Island was colonised by a Swiss Baron called Alfredo von Rodt, who bought it from the Chilean government.
He took a group of 63 relatives, friends and workers to live on the island and most of today’s inhabitants are descended from these individuals. Tellingly, families who have moved to the island more recently ― despite sharing the same lifestyle and education ― have language impairment at the expected level of 4 per cent.
More than 80 per cent of the children with SLI belonged to a big family tree that goes back to two of the founding brothers, suggesting that the language impairment may be caused be a genetic mutation. This is unusual as we know that, for most language disorders, the genetic risk is carried across several genes, each of which have only a small effect.
Pia was aware that genetics are an important factor in the risk of developing SLI through her discussions with Gina Conti-Ramsden, a lead researcher in the SLI consortium (SLIC). This research group have looked at more than 300 British families affected by SLI and have identified two genes, known as CMIP and ATP2C2, that may play a role in SLI.
She began to collect DNA samples from the islanders and performed an initial study of a genetic variant close to these genes. She found a correlation between the genetic identity of individuals at this variant and their language ability supporting the idea that genetics might be involved.
As these studies progressed, so did genetic technologies. It soon became apparent that a larger scale genetic study would be feasible ― and that’s where I come in.
Funded by the MRC, my team at the University of Oxford has worked with Pia’s to look at the widespread genetic variation of the islanders. An initial study identified five chromosome regions (on chromosomes 6, 7, 12, 13 and 17) that were more similar in islanders with SLI than is expected by chance. Now we’re doing a more in-depth characterisation involving genetic sequencing of islanders with language impairment. This will help us to pinpoint the important mutations more precisely.
We hope that by studying this unique population, we can learn more about why some children find it difficult to learn language. Although SLI is a common condition, we have little understanding as to what causes it at the biological level.
So our story has only just begun, but for the islanders it is just another chapter in their rich and colourful history.
Dianne Newbury is an MRC Career Development Fellow at the Wellcome Trust Centre for Human Genetics. Read more about the research of the Newbury lab.