GENDER DIFFERENCES IN THE HERITABILITY OF SEASONAL MOOD CHANGE

The study estimated gender differences in the magnitude of genetic and environmental influence in seasonal mood change. The self-report Seas onal Pattern Assessment Questionnaire (SPAQ) was completed by 339 volu nteer reared-together twinpairs (187 monozygotic pairs, 152 dizygotic pairs) and analysed using biometric genetic models. The SPAQ yields a global seasonality score (GSS) which is an index of change in sleep pa tterns, social activities, mood, weight, appetite, and energy level. T he GSS was significantly heritable among males and females, estimated to account for 69% and 45% of the total variance, respectively. For th e individual symptoms, changes in sleep patterns, social activities, m ood, appetite, and energy levels were accounted for primarily by addit ive genetic effects in both males (median, 45.5%) and females (median, 30.5%). For both sexes, weight changes were not heritable. Sex-by-gen otype analyses suggested that the genetic factors influencing female s easonality may not be the same as those influencing male seasonality. (C) 1997 Elsevier Science Ireland Ltd.