Time, memory and the heritability of major depression

Objective. Although family. twin and adoption studies have suggested that l ifetime major depression (MD) is a heritable condition, nearly all these st udies have relied for the diagnosis on long-term human memory, which is fal lible and potentially biased. Could the estimates of heritability of MD be biased by the well-demonstrated genetic influences on memory? Methods. Both members of 858 female-female twin pairs from a population-bas ed registry were personally interviewed at least three times over 9 years. The interview assessed a history of depressive onsets and recoveries in the last year to the nearest month. We examine heritability of MD using four r ecall intervals: last year, last 6 months, last 3 months and current month. Results, Examining the occurrence of one or mure depressive episodes across all three interviews, heritabilities of MD (95 % CI) for the four time per iods were: 0(.)41 (0(.)27-0(.)54), 0(.)41 (0(.)26-0(.)55), 0(.)35 (0(.)16-0 (.)52) and 0(.)34 (0(.)11-0(.)55). These heritability estimates did not dif fer significantly from one another. A similar pattern was found if heritabi lity was assessed for the number of interviews in which criteria for MD wer e met. Conclusion. Modelling results suggest that the heritability of MD was not i nfluenced by the duration of the required recall. Genetic influences on hum an recall do not appear to contribute substantially to estimated heritabili ty of MD.