Although only a small percentage of North Americans experience full-blown
seasonal affective disorder—about 1 percent of Americans and 2 percent
of Canadians—a much larger percentage—between 10 percent and 15
percent—report depression accompanied by increased eating and weight
gain during the fall and winter. Moreover, of this larger percentage, a
substantial number also engage in binge eating.
Now a gene variant linked to seasonal affective disorder binge eating
appears to have been identified. It is a variant of the dopamine-4 receptor
gene called the seven-repeat allele.
The study was headed by Robert Levitan, M.D., an associate professor of
psychiatry at the University of Toronto. Results appeared in the November 2004
Biological Psychiatry. "Pending replication in other
samples," the scientists wrote, "these results point to a genetic
vulnerability factor that could help in the early identification and treatment
of women at higher risk for seasonal weight gain associated with binge-eating
The dopamine-4 receptors appear to be active in limbic areas of the brain
involved in cognition and emotion. There are seven known variants of the gene
that codes for these receptors; the seven-repeat allele is one. Between 25
percent and 35 percent of Caucasians and up to 65 percent of some
American-Indian populations possess at least one copy of this version.
Levitan and his colleagues previously found a link between the seven-repeat
allele and obesity in women with seasonal affective disorder, implying that
the allele might bring about weight gain via binge eating. They then undertook
another study to investigate this hypothesis.
The study sample consisted of 131 women, mostly Caucasian, who met
DSM-IV criteria for major depression with a winter seasonal pattern
and who were also found, with the Structured Clinical Interview for
DSM-IV, to engage in increased eating during winter depressive
episodes. Using the same instrument, the researchers found that 32 of the
subject engaged in binge eating.
Blood samples from the subjects were sent to the Center for Addiction and
Mental Health Neurogenetics Laboratory, where DNA from white blood cell
samples from the subjects were examined for various versions of the dopamine-4
Of the 131 subjects, 46 (35 percent) had at least one version of the
seven-repeat allele. Further, these 46 subjects had a significantly greater
maximal lifetime body-mass index than subjects without the version. Moreover,
of the 46 subjects with at least one version, 18 (39 percent) engaged in binge
eating, whereas only 14 of the remaining 85 subjects (17 percent) did
so—a highly significant difference.
So the seven-repeat allele may be responsible, at least in part, for
excessive weight gain during winter depression and may bring about that weight
gain via binge-eating behavior.
The finding has some early-detection and even prevention implications,
Levitan said in an interview. "For example, one could follow kids who
have the seven-repeat allele.. .to identify emerging mood disorders and
increased eating behavior as early as possible. Early intervention with a
variety of modalities could help prevent the full-blown seasonal affective
disorder—binge eating syndrome from developing. This would also be a
high-priority group for nutritional counseling and exercise programs early in
The result might also lead to some novel treatments for winter depression
binge eating, Levitan noted. But first, he stressed, the result must be
replicated in other studies, "then one must understand the actual
mechanisms involved. Where in the brain is this mediated? How does the gene
affect brain function?"
Also in need of exploring is whether the seven-repeat allele that has been
associated with seasonal affective disorder binge eating is the same
seven-repeat allele that has been linked to attention-deficit/hyperactivity
disorder, impulsivity, novelty seeking, and substance abuse. If the same
seven-repeat allele is implicated in all of these disorders, then "binge
eating may be just one manifestation of a genetic vulnerability that leads to
many behavioral problems over time in the same individual," Levitan
The study was funded by the Ontario Mental Health Foundation and the
National Alliance for Research on Schizophrenia and Depression.
An abstract of "The Dopamine-4 Receptor Gene Associated With
Binge Eating and Weight Gain in Women With Seasonal Affective Disorder: An
Evolutionary Perspective" can be accessed online at<www.elsevier.com/locate/biopsych>
by clicking on the November 1, 2004, issue, and then the report