Perinatal depression is defined as depressive illness which emerges during pregnancy (antenatal depression) or following childbirth (postpartum depression). We have limited information regarding the genetic basis of perinatal depression, but several studies suggest that the heritable component for perinatal depression may be greater than that observed for major depressive disorder which is unrelated to pregnancy. Several studies have shown familial clustering of perinatal depression.
- Murphy-Eberenz and colleagues reported that the siblings of women with perinatal depression were 3.96 times more likely to have postpartum depression than women without affected siblings.
- Forty and colleagues observed that when they confined their analysis to postpartum depression with its onset within 6–8 weeks after childbirth, 42% of women with a family history of PPD experienced depression following their first delivery, whereas only 15% of women with no such family history experienced depression after delivery.
- An Australian study of 1,676 twin pairs estimated that the heritability of postpartum depression was 25%.
Many women with perinatal depression also have episodes of depression that are not associated with childbearing, and researchers have postulated that perinatal depression is merely an episode of major depressive disorder which emerges sometime during pregnancy or the postpartum period. Others, however, believe that perinatal depression is partly or wholly distinct from major depressive disorder: “According to this view, the biological underpinnings of perinatal depression differ from those of nonperinatal depression in that sensitivity to the dramatic fluctuations in gonadal hormone serum concentrations during the perinatal period probably play a pathogenic role . This implies that perinatal depression and nonperinatal depression are at least partially different disorders, with perinatal depression featuring distinctive genetic and environmental etiological risk factors.”
In a recent study published in the American Journal of Psychiatry, researchers investigated the relative contribution of genetic and environmental influences on perinatal depression, and the genetic overlap between perinatal depression and non-perinatal depression. In this study, the lifetime version of the Edinburgh Postnatal Depression Scale (EPDS) was administered to 3,427 Swedish female twins in the Swedish Twin Registry. Population data from over 580,000 sisters and national treatment registers were used to estimate the heritability of perinatal depression, the heritability of nonperinatal depression, and the genetic and environmental overlap between the two.
This is, to date, the largest genetic epidemiological study of perinatal depression. Using data from the twins, the heritability of perinatal depression was estimated at 54% (95% CI=35%?70%), with the remaining variance attributable to non-shared environmental factors (46%; 95% CI=31%?65%). Using data from the siblings, the heritability of perinatal depression was estimated at 44% (95% CI=35%?52%) and the heritability of non-perinatal depression at 32% (95% CI=24%?41%). The authors estimated that about one-third of the genetic contribution was unique to perinatal depression and not shared with non-perinatal depression, suggesting only partially overlapping genetic etiologies for perinatal depression and non-perinatal depression.
Given these findings, the authors recommend that perinatal depression be prioritized for genomic discovery efforts. Thus far, many of the studies exploring the genetics of perinatal depression have focused on genes that have been implicated in the etiology of non-perinatal depression, including genes regulating the synthesis of the serotonin transporter and others associated with the metabolism of various neurotransmitters. The results have been mixed, which may reflect heterogeneity in the studied populations. (This review summarizes the medical literature regarding the genetics involved in perinatal depression.)
Perinatal depression is a complex disorder, where there is an interaction between genetic vulnerability, hormonal changes, and environmental factors. As with other psychiatric disorders, genetic factors alone may not be sufficient to cause the illness. The emergence of psychiatric illness is often dependent on epigenetics, and certain environmental triggers may be required for psychiatric illness to develop.
Ruta Nonacs, MD PhD
Forty L, Jones L, Macgregor S, et al: Familiality of postpartum depression in unipolar disorder: results of a family study. Am J Psychiatry 2006; 163:1549–1553.
Murphy-Eberenz K, Zandi PP, March D, et al: Is perinatal depression familial? J Affect Disord 2006; 90:49–5.
Treloar SA, Martin NG, Bucholz KK, et al: Genetic influences on postnatal depressive symptoms: findings from an Australian twin sample. Psychol Med 1999; 29:645–654.