Size Matters: Social Disadvantage, Stress and Chromosomes

Telomere

 

The length of a telomere – a region of repetitive DNA found at the end of a chromosome  – can be up to 19% shorter in children from deprived backgrounds, according to new research conducted by Princeton University, US.

The findings, published in the journal for Proceedings of the National Academy of Sciences, link social environment with health suggesting that disadvantaged backgrounds affect life at a chromosomal level.

 

The Shoelace Ends of DNA

News Medical likens the function of Telomeres to the function of ‘aglets’ – the ends of shoelaces that prevent the lace from fraying. A telomere protects a cell’s chromosomes from fusing with each other or rearranging, abnormalities which can lead to cancer. Cells are normally destroyed when their telomeres are consumed. The website adds that most cancers are the results of ‘immortal’ cells which have ways of evading this programmed destruction.

 

Study Cohort

Using data from a birth cohort study, researchers studied a group of African-American boys, an ethnic group not studied closely before in terms of deprivation and effect on length of telomere. Boys were selected as they proved more susceptible to environmental stress than girls. Of the 40 boys, 20 were from severely disadvantaged backgrounds and 20 from highly advantaged environments.

Those children who grew up in highly disadvantaged environments proved to consistently have shorter telomeres at the age of 9 compared to those who grew up in highly advantaged environments.

 

Genetic Variation

The strength of the association between telomere length and social environment was seen to be moderated by genetic variation in serotonin and dopamine pathways.

Boys with a high genetic sensitivity had the shortest telomere length when exposed to disadvantaged environments, and the longest when exposed to advantaged environments.

Researchers claim that this is the first study to document a genetic-social environment interaction for telomere length – a biomarker for stress exposure.

 

Findings

Disadvantaged social environments are associated with adverse health outcomes. The report claims that this is partly caused by exposure to chronic stress with telomere length shorter found in adults of disadvantaged social standing and in cases of depression.

The finding that stress contributes to poor health is further compounded by significant associations found between telomere length and the following;

  • low income
  • low maternal education
  • unstable family structure
  • harsh parenting

These effects were seen to be moderated by genetic variants.

Results were consistent with the hypothesis of ‘differential susceptibility’ – one which suggests that individuals can be more vulnerable or less vulnerable to the impact of environments, both good and bad, depending on their genetic disposition.

The subjects in the cohort with the highest genetic sensitivity scores had the shortest telomere length when exposed to disadvantaged social environments, and the longest telomere length when exposed to advantaged environments.

 

DNA Replication

The ends of chromosome shorten with each cycle during DNA replication. The repetitive telomere sequence is sacrificed to protect genetic information near the ends of chromosomes.

Gradually, telomere ends become shorter in length and this shortening is associated with the cell activated signalling events that produce replicative ageing.

Stress appears to augment replicative telomere shortening and could evoke physiological weathering in a similar way to ageing.

Possible behavioural mediators of the negative association between stress and telomere length include:

  • smoking
  • mental illness (in particular, depression)
  • caregiver stress
  • obesity

 

Deprivation and Education

The study of African-Americal boys showed that living in a disadvantaged environment lead to a 19% shortening of telomere length.

However, a doubling of the family income led to a 5% increase in telomere length.

Education of the mother was a game changer. Having a mother with a high school degree is associated with a 32% increase in a child’s telomere length, and having a mother with at least some post secondary education is associated with a 35% increase.

Family economic status was a significant predictor of a boy’s telomere length measured in middle childhood.

A low score on the parenting quality index was associated with a 3% decrease in a boy’s telomere length.

Disruptive change proved harmful. Being exposed to multiple changes in family structure was associated with a 40% decline in a boy’s telomere length.

Researchers suggest that the study raises intriguing questions about the workings of the gene-social environment. Genetic ‘architecture’ is the decider on how, and to what extent, our environments build us up or knock us down;

“Our findings on gene–social environment interactions raise intriguing questions about the mechanisms involved. We suggest that an individual’s genetic architecture moderates the magnitude and direction of the physiological response to exogenous stressors.” (excerpt)

 

Notes

PNAS: Social disadvantage, genetic sensitivity, and children’s telomere length – http://www.pnas.org/content/111/16/5944

 

Image 

creative commons licensed (BY) flickr photo by ex_magician: http://flickr.com/photos/ex_magician/4264098269

 

 

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