People exposed to adverse psychosocial experiences before the age of 18 have enduring emotional, immune, and metabolic abnormalities, that in turn contribute to them being at greater risk for age-related disease.  In other words, bad stuff 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 of incidents. The more categories of things you experience, the greater the risk of problems in adulthood. The categories are:

  • ace_pyramid_wotextrecurrent 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 specifically associated with later life depression and found these (Alciata, 2012):

  • verbal abuse from parents
  • mental cruelty
  • excessive punishment by parents
  • abuse by an adult outside the family
  • parental mental disorder
  • poverty
  • home conflict
  • excessive sharing of 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 factor is genetics.


Genetics: the long and the short of it

A great deal of research goes into which genes are associated with depression, much of it focussed on the serotonin transporter gene, as explained by Kuzelova et al (2010):

dnaBoth 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 the serotonin transporter gene has two forms (‘alleles’) which have 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.  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 (“risk allele”) 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 gene 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 (albeit rather quiet) video explaining alleles:

The Adverse Childhood Experiences (ACE) Study

A Danese at al (2009) Adverse Childhood Experiences and Adult Risk Factors for Age-Related Disease Depression, Inflammation, and Clustering of Metabolic Risk Markers

A Alciata (2012) Different Types of Childhood Adverse Experiences and Mood Disorders

H Kuzelova et al (2010) The serotonin transporter gene (5-HTT) variant and psychiatric disorders: review of current literature

G Kenna et al (2013) Association of the 5-HTT gene-linked promoter region (5-HTTLPR) polymorphism with psychiatric disorders: review of psychopathology and pharmacotherapy

childhood adversity and depression in later life

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