Seasonal Affective Disorder (SAD): 5-HTTLPR gene theory

Research now suggests that SAD has a genetic component. Simply put, low-sunlight is not an equal opportunity depressant. Some genetic groups are more affected by SAD than others. Specifically, the 5-HTTLPR gene has been found to be expressed differently in SAD patients.

One particular gene known as 5-HTTLPR has received a lot of attention from researchers as it has been found to be expressed differently in SAD patients.

The 5-HTTLPR gene is involved with the function of serotonin (5-HT).

Researchers have been careful to explain that this gene may not be the root cause of SAD but is certainly involved in the disease process and the production of symptoms.

Other research has implicated the 5-HT2A gene, which is also
involved with serotonin function. This gene they say is associated with the depressive symptoms of SAD but does not explain the seasonality of the disorder.

Many of the genetic studies looking at particular genes have also looked patients families and found that, as with most mental illness, there is often a family history of mental health problems. This suggests the 5-HTTLPR gene may be a top-line 'regulator' of *many* mental health issues.

The general consensus is the farther north one goes (in the northern hemisphere), the greater the number of people suffering from SAD. A major review of SAD research found that in both North America and Europe, that SAD cases increase as a percentage of population the higher the latitude.

It's not that simple. The same survey showed North America has *twice* as many cases of SAD than Europe. This suggests lower light levels at more northerly latitudes are indeed an important risk factor for SAD, but are not the only factor.

Some speculate the higher incidence of SAD in North America can be attributed to greater racial diversity than present in northern European nations or to other cultural and social factors. The melting pot of the United States is full of individuals from central, tropic and sub-tropic latitudes.

A person with genetic roots from central America who now lives in Manitoba might have more sensitive serotonin and melatonin responses to low-light than an Inuit.

That response may be regulated by the 5-HTTLPR gene.

Think you might have Seasonal Affective Disorder (SAD) ?
Common symptoms for SAD:

• Afternoon slumps with decreased energy and concentration
• Carbohydrate cravings
• Decreased interest in work or other activities
• Depression that starts in fall or winter
• Increased appetite with weight gain
• Increased sleep and excessive daytime sleepiness
• Lack of energy
• Slow, sluggish, lethargic movement
• Social withdrawal

 
Common treatments for SAD mirror that of other types of depression; including talk therapy and anti-depressant medications.  Light therapy, at specific times, using a full-spectrum light source to mimic the sun may also help.

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National Alliance on Mental Health: Seasonal Affective Disorder