A genetic mutation that causes photosensitivity

New research by a large international consortium has identified numerous gene variants associated with increased risk of photosensitivity in epilepsy¹. 

Photosensitivity, defined as an abnormal brain response to flickering light, sometimes occurs in people with a rare form of epilepsy caused by mutations in various genes, including CHD2.

Sanjay Sisodiya, of the Institute of Neurology in London, and his colleagues compared the CHD2 gene sequence from 580 people with various types of photosensitive epilepsy and nearly 34,500 healthy controls, and identified 11 unique mutations in the people with epilepsy. 

They then reduced activity of the CHD2 gene by half in zebrafish embryos, and found that this markedly enhanced the light sensitivity of the larvae. 

The findings suggest that human mutations cause photosensitivity by partially or fully inactivating the CHD2 gene. Researchers know that this gene does not encode an ion channel, the barrel-shaped membrane proteins that are crucial for generating nervous impulses, but its functions are otherwise unclear. 

Although the gene is not directly involved in epilepsy, the findings also provide fresh insights into the mechanisms contributing to the abnormal cortical excitability that is a hallmark of the condition. 

“CHD2 is also involved in embryonic neurogenesis, suggesting a number of ways in which cortical excitability can be modulated beyond ion channels alone,” says Sisodiya.

“We are [now doing] functional work with collaborators, and searching for other mutations which may influence photosensitivity and cortical excitability.”

The research team includes Bosanka Jocic-Jakubi from the department of Paediatric neurology of Al Sabah hospital in Kuwait.    

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