Many people claim to suffer from seasonal affective disorder, a downturn in mood brought on by the long grey winter months. It's a poorly understood condition, but a new study claims a genetic mutation in the eye may be to blame.
As many as 6% of the US population suffer from seasonal affective disorder (SAD). The severity of the symptoms range from individual to individual. For some it leads to a temporary drop in mood, particularly in the mornings. For others it's the start of a debilitating depression. Treatment usually involves sitting in front of a bank of lights to try and fool the brain into thinking the days are longer, and brighter.
Little is known about seasonal affective disorder and genes, but as some researchers claim that up to 30% of SAD sufferers come from families with the condition, a genetic explanation is a possibility. It makes research led by the University of Virginia all the more welcome.
Genetic Cause for Seasonal Affective Disorder?
Researchers in this study reckon that SAD may be linked to a genetic mutation in melanopsin, a photopigment gene in the eye. The genetic mutation makes the SAD sufferer less sensitive to light.
To find out whether a gene is responsible for seasonal affective disorder researchers recruited 220 volunteers. 130 were SAD sufferers and 90 were not.
They carried out genetic tests on the participants and found that seven of them had genetic mutations on both versions of the melanopsin gene. Those seven all suffered from SAD. The scientists calculated that a person with both mutations was five times more likely to suffer from SAD than someone without.
"While a person diagnosed with SAD does not necessarily carry the melanopsin mutation, what we found strongly indicates that people who carry the mutation could very well be diagnosed with SAD." So said Prof Ignacio Provencio who carried out the research with colleagues at the University of Virginia. He continued, "We think that if an individual has two copies of this gene, he or she has a reasonable chance of having the disorder."
Seasonal Affective Disorder Treatment
The exact mechanism of how the genetic mutation leads to the symptoms of SAD has not been worked out. At the moment what the researchers have done is to isolate a possible genetic explanation and show a statistical association with SAD.
The photopigment that the melanopsin gene codes for is a retinal light-sensitive protein that is not involved directly in vision. It's linked to non-visual responses such as circadian rhythms and sleep. Somehow the genetic mutation must upset these processes to lead to the mental responses that are so familiar to so many people.
Undoubtedly further research is needed, but the discovery of a genetic mutation and its possible link to SAD is starting to offer some sort of explanation as to why people have the condition. It may also lead to new kind of therapies to treat or cure a condition that blights many lives.