Seasonal changes in mood and behavior. The role of genetic factors.
BACKGROUND
Seasonal rhythms in mood and behavior (seasonality) have been reported to occur in the general population. Seasonal affective disorder, a clinically diagnosed syndrome, is believed to represent the morbid extreme of a spectrum of seasonality. Two types of seasonality have been clinically described: one characterized by a winter pattern and a second by a summer pattern of depressive mood disturbance.


METHODS
By using methods of univariate and multivariate genetic analysis, we examined the relative contribution of genetic and environmental factors to the risk of seasonality symptoms that were assessed by a mailed questionnaire of 4639 adult twins from a volunteer-based registry in Australia.


RESULTS
Seasonality was associated with a winter rather than a summer pattern of mood and behavioral change. In each behavioral domain (ie, mood, energy, social activity, sleep, appetite, and weight), a significant genetic influence on the reporting of seasonal changes was found. Consistent with the hypothesis of a seasonal syndrome, genetic effects were found to exert a global influence across all behavioral changes, accounting for at least 29% of the variance in seasonality in men and women.


CONCLUSIONS
There is a tendency for seasonal changes in mood and behavior to run in families, especially seasonality of the winter type, and this is largely due to a biological predisposition. These findings support continuing efforts to understand the role of seasonality in the development of mood disorders.
Department of Psychiatry, Washington University School of Medicine, St Louis, Mo, USA.
P A
PA
Madden
A C
AC
Heath
N E
NE
Rosenthal
N G
NG
Martin
D000328:Adult; D000339:Affect; D000368:Aged; D001066:Appetite; D001315:Australia / Q000453:epidemiology; D001835:Body Weight; D004200:Diseases in Twins / Q000453:epidemiology / Q000235:genetics; D005190:Family; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012042:Registries; D016574:Seasonal Affective Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*; D012621:Seasons; D012890:Sleep; D012931:Social Environment