Harm avoidance, reward dependence, novelty seeking, and self-directedness have traitlike characteristics that are related to the familiality of depression. Cooperativeness, self-transcendence, and persistence are also familial, but this appears to be unrelated to depression.

The human serotonin transporter gene (hSERT) is a strong candidate for involvement in the pathogenesis of mood disorder and, using a UK Caucasian case-control sample, Collier et al found a significant association between bipolar disorder and the 12 allele of the VNTR polymorphism in intron 2 of this gene. In a European collaborative sample, Collier et al found a significant association between affective disorder and a functional deletion polymorphism in the promoter of hSERT. We have undertaken association studies using these polymorphisms in a British Caucasian sample comprising 171 DSM-IV bipolar probands, 80 DSM-IV major depression probands and 121 unrelated controls matched to bipolar probands for age, sex and ethnicity. We found no association between the promoter deletion and affective disorder but our findings with the VNTR polymorphism are similar to those of Collier and colleagues: we found a significant excess of the 12 repeat allele in bipolar probands (P = 0.031, one-tail) with a suggestion of a gene dosage effect (using genotypes bearing no 12 repeat allele as baseline, the increased risks conferred by genotypes bearing 12 repeat alleles were: heterozygote, OR = 1.24; homozygote, OR = 1.76). Our findings add to the evidence that variation at or near hSERT influences susceptibility to bipolar disorder in the British Caucasian population.

Neither extraversion nor neuroticism measures trait vulnerability to depression, and neuroticism scores mainly reflect symptoms of depression.

Although there was modest evidence for temporal stability and familiality for some DAS-24 subscale scores, dysfunctional attitudes were predominantly influenced by current low mood, and therefore reflect the state of being depressed rather than a familial vulnerability trait underpinning depression.

The SSQ measures a familial personality trait and depression is associated with lower scores. Although high sensation-seeking is associated with a higher rate of life events, these carry little threat.