Discovery of a rare genetic variant provides clues to understanding common speech and language difficulties
Tuesday, 28 April 2020
An international team of scientists led by Oxford Brookes University have discovered a rare genetic variant which helps us to understand the relationship between hearing and speech and language.
Auditory Processing Disorder (APD) is characterised by difficulties filtering out background noise which can lead to problems understanding speech and language. APD and language disorders are common childhood conditions and are thought to affect up to 10% of the childhood population in the UK, but it is not understood why some children have these difficulties or how the conditions relate to each other.
In a new study, scientists aimed to characterise some of the genetic mechanisms that alter filtering processes which then have a knock-on effect on developing language.
The team investigated the DNA sequence of a family of 12 individuals, eight of whom had filtering and speech difficulties, and searched for rare genetic variants that may contribute to these difficulties.
The subtle hearing difficulties we observed are not easily identified on routine clinical testing and typically go undetected. We believe that early detection by specific assessment of low frequency hearing combined with genetic assessment is an important step towards better diagnosis and better prognosis of those at risk.Dr Dianne Newbury, Senior Lecturer in Medical Genetics and Genomics, Oxford Brookes University
Dr Dianne Newbury, Senior Lecturer in Medical Genetics and Genomics at Oxford Brookes University and lead co-author of the study explains, “We found a change in a gene called USH2A, which led to the production of only half the amount of protein.
“Previous studies have shown that when the USH2A protein is completely absent, this results in a complete loss of hearing which is present at birth and is known as Usher Syndrome. However, the effects of intermediate levels of the protein are not known, so we investigated whether intermediate USH2A levels could contribute to disrupted filtering and speech processes in the family.”
The team looked at genetic data from a large UK population sample and found that children with disrupted USH2A protein levels were not deaf, but showed very subtle difficulties in hearing at low frequencies. This is thought to have an impact on their language development.
Dr Newbury adds: “The subtle hearing difficulties we observed are not easily identified on routine clinical testing and typically go undetected. We believe that early detection by specific assessment of low frequency hearing combined with genetic assessment is an important step towards better diagnosis and better prognosis of those at risk.”
To get a better idea about the relationships between USH2A and hearing, the research team at the University of Connecticut observed mice which had intermediate USH2A protein levels. They found results which mirrored Oxford Brookes’ work in the population sample. The mice showed low frequency hearing impairment, altered processing of sounds and they squeaked louder. This led the team to believe that the level of the USH2A protein is related to speech and language when hearing is altered.
The identified USH2A gene makes a protein that connects tiny sensory hair cells (stereocilia) within the cochlea in the inner ear. When sound waves reach the cochlea, they bend the hair cells. Link proteins such as USH2A are essential so hair cells can bend synchronously and create electrical signals which travel to the brain for processing.
Further investigations of the USH2A gene will provide a better understanding of the filtering processes and the way they impact areas of language development.
The study, Multi-level evidence of an allelic hierarchy of USH2A variants in hearing, auditory processing and speech/language outcomes, has been published in Communications Biology.