FuturePundit points me to new work on a genetic mutation which might predispose one to Season Affective Disorder, A missense variant (P10L) of the melanopsin (OPN4) gene in seasonal affective disorder:
SAD participants had a higher frequency of the homozygous minor genotype (T/T) for the missense variant rs2675703 (P10L) than controls, compared to the combined frequencies of C/C and C/T. Individuals with the T/T genotype were 5.6 times more likely to be in the SAD group than the control group, and all 7 (5%) of individuals with the T/T genotype at P10L were in the SAD group.
It looks like there’s some between population difference:
