Depressive and psychosomatic symptoms in twins with special reference to co-twin dependence

We analyzed depressive and psychosomatic symptoms in relation to co-twin dependence in 419 twins at the age of 22 to 30 years. Depressive symptoms were assessed, as previously, with Children's Depression Inventory modified to be suitable for this age and reported as a total score and three subscales (low self-confidence, anhedonia and sadness) based on factor analysis as reported in a previous epidemiological study conducted in Finland. Items assessing nervous complaints and somatic symptoms were adapted from Finnish studies of juvenile health habits. Inter-twin dependence decreased with increasing age in both genders. Monozygotic twins, especially monozygotic females, reported most often to be dependent on their co-twin. When the symptom reporting was evaluated in relation to co-twin dependence, no relation was found between co-twin dependence and depressive symptom reporting. However, dependence-independence imbalance within twin pair was associated with elevated levels of depressive and psychosomatic symptoms, especially in twins who perceived themselves as dependent and the co-twin as independent. We conclude that there was no relation found between co-twin dependence and depressive symptom reporting in male and female twins except for the few imbalance cases, where most symptoms were reported by those dependent twins who felt their co-twin as independent.