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Tuesday, 20 April, 1999, 12:19 GMT 13:19 UK
Winter depression runs in families
Winter scene
Winter can lead to depression in some people
A condition that causes sufferers to find wintertime intolerably miserable and depressing may be caused by a faulty gene, scientists believe.

Seasonal Affective Disorder (SAD) can cause depression, oversleeping, overeating and food cravings for carbohydrates.

It can be treated with light therapy, which involves sitting in front of a bank of lights, or with anti-depressant medication such as Zoloft.

SAD is known to run in families, and is more common in certain countries.

Most of these are at northern latitudes, where there is little daylight in the winter.

Doctors in Sweden say SAD affects up to 20% of Sweden's 8.5 million people to some degree.

However, people living in some far northern countries such as Iceland seem to be less prone to the condition.

Now researchers from the National Institute of Mental Health in Bethesda, Maryland, believe they have discovered a gene that may make people prone to SAD.

The gene is known as 5-HTTLPR, and comes in short and long versions.

The short version lacks some of the components that make up DNA, the material which contains the blueprint for the genes.

Short copies

SAD sufferers crave carbohydrates in winter
A study of about 90 people who complained of SAD and 75 "controls" without the condition showed that in the controls, about 50% of people have two copies of the long gene, and 50% either have two short copies or a long and a short copy.

Of the SAD patients, three-quarters had at least one short copy of the gene.

The researchers found that people with two short copies of the gene were much more likely to suffer from SAD.

A second study of 200 people taken from the general population around Bethesda showed that about 4% had SAD or SAD symptoms.

Those who had the SAD symptoms were also more likely to have a short version of the gene.

Researcher Dr Leo Sher believes that the short version of the 5-HTTLPR gene affects a person's response to light. This could be modified by anti-depressants.

However, Dr Sher also suspects SAD could also have a purely psychological component.

The symptoms of SAD could simply be a natural and desirable response to winter, he said.

"In nature, animals are generally less functional in winter."

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