PeopleÂ exposed to adverse psychosocial experiences before the age of 18 haveÂ enduring emotional, immune, and metabolic abnormalities, that in turn contribute to them being atÂ greater risk for age-related disease. Â In other words, bad stuffÂ that happens in childhood predisposes you to physical and mental health problems later in life. Depression is one such problem.
According to the seminal Adverse Childhood Experiences (ACE) study, the number of bad incidents matters less (in terms of risk of later problems) than the number of categories ofÂ incidents. The more categories of things you experience, the greater the risk of problems in adulthood. The categories are:
- recurrent physical abuse
- recurrent emotional abuse
- contact sexual abuse
- one or no parents
- emotional neglect
- physical neglect
- mother is treated violently
- an incarcerated household member
- an alcohol and/or drug abuser in the household
- family member who is chronically depressed, mentally ill, institutionalised, or suicidal
The key concept underlying the study is that stressful or traumatic childhood experiences are a common pathway to social, emotional, and cognitive impairments that lead to increased risk of unhealthy behaviours, risk of violence or re-victimisation, disease, disability and premature mortality .
This association between early adversity and later problems relates to stress-sensitive biological systems in the body, namely, the nervous, immune, and endocrine/metabolic systems (Danese et al, 2009).
Early adversity and depression
Researchers have looked in more detail at the type of early experiences specificallyÂ associated with later life depression and found these (Alciata, 2012):
- verbal abuseÂ from parents
- mental cruelty
- excessive punishment by parents
- abuse by an adult outsideÂ the family
- parental mental disorder
- home conflict
- excessive sharing ofÂ parental problems with children
This is all very well, but does not explain why one individual suffers from depression in later life while another, with similar childhood experiences, does not. One important factorÂ is genetics.
Genetics: the long and the short of it
AÂ great deal of researchÂ goesÂ into which genes are associated with depression, much of itÂ focussed on theÂ serotonin transporter gene, as explained by Kuzelova et al (2010):
Both serotonin and the serotonin transporter, which transports the neurotransmitter serotonin from synaptic spaces into presynaptic neurons, play an important role in the pathophysiology of several psychiatric disorders. Mutations associated with the serotonin transporter gene may result in changes in serotonin transporter function.
The serotonin transporter gene promoter variant, consisting of a long (L) and a short (S) variant, is one of the major factors which contribute to the aetiology of many psychiatric disorders. In this regard, many studies have been published on association of this variant with various psychiatric disorders.
In very simplistic terms, it seems that theÂ serotonin transporterÂ gene has two formsÂ (‘alleles’) which haveÂ been described as ‘long’ or ‘short’, and a person can have one of three combinations within their gene: short-short, short-long or long-long. Â Each combination is associated with differing risk of developing mental health problems, but it’s a confusing picture, as this review of the literature indicates (Kenna et al, 2013):
Decreased transcriptional activity of the S allele (â€œrisk alleleâ€) may be associated with a heightened amygdala response leading to anxiety-related personality traits, major depressive disorder, suicide attempts, and bipolar disorder.
By contrast, increased transcriptional activity of the L allele is considered protective for depression but is also associated with completed suicide, nicotine dependence, and attention deficit hyperactivity disorder.
Unfortunately, the results of studies assessing the association between the serotonin transporter geneÂ and depression are inconsistent, but the search continues for the genetic culprits.
References and further reading
Here’s a helpful video on genes for beginners (like me):
And another helpful (albeitÂ rather quiet) video explaining alleles:
The Adverse Childhood Experiences (ACE) Study
A Alciata (2012) Different Types of Childhood AdverseÂ Experiences and Mood Disorders