Gene x Environment

Plomin et al (2005)

• separating out nature and nurture is said to be both impossible and unproductive
• the importance of genes as well as environment in the eitology of individual differences in behaviour is increasingly accepted in science as well as in society.
• we predict that this trend will accelerate in the postgenomic era as specific genes are found that are responsible for the heritability of behavioural disorders and dimensions. 
• but these new findings also raise many new problems including ones with human dignity. 
• these issues have been addressed in a report by the Nuffield Council on Bioethics (2002)

- Two hypotheses dominated philosophical thinking and still dominate much thinking today:

• people are born the way they are (genetic determinism)  this is like the nativist position
• people learn to be the way they are (environmentalism)  this is like the empiricist position

 - the formulation of a 'gene vs environment' debate is extremely misleading. It would be impossible for a person to exist without ever interacting with the environment. 

• phenotype: the apparent, observable measurable characteristics of the individual... behaviour is a phenotype, cognition is a phenotype.
• genotype:  the genetic composition of the individual. Tells us which genes are present but doesn't give any direct indication of how those genes are behaving.
• genetic variant: the contribution of different versions of the human genome to individual differences. Everyone has the same set of genes, but individuals possess slightly different versions of those genes, called genetic variants or alleles.
• alleles: genes for the same characteristic located in the same place on a pair of chromosomes
• phenotype-genotype distinction: presents the relationship between observable and 

Eugenics (early 20th century)

• Hogben and Fisher were the first to debaate the G x E interaction.
• Fisher was an enthusiastic eugenicist. Where interaction did crop up, he easily solved the problem, by transforming the scale of measurement to make the problem go away.  
• Hogben was an anti-eugenicist. He argued that interdependence was common in nature, and should be sought out. He felt that the interaction was caused by a developmental relationship between nature and nurture and that this was important in providing the causal mechanisms of the developmental process. 

IQ and race

- Jensen (1969) drew on quantitative genetic studies that put the heritability of IQ at about 80%, surmising from this that environ. differences could not 100% explain away the gap in attainment of African Americans and Caucasians. Got called out for being racist, with thoughts about intelligence being determined by race known as 'Jensenism'

Interaction in the serotonin transporter gene controversy

• Genome-wide association stuy and the gene-environment interaction study (Moffit & Caspi) were both used to try and replicate earlier findings of links with genes to complex human traits.
• Gene-environment interaction strategy was the first to generate results, combining earlier candidate genes from the genetic side (like 5-HTTLPR) with an environmental factor (like exposure to stressful events)

• Short 's' allele x life stress & maltreatment -> increased risk of depression in 's' homozygotes experiencing adversity 
• The 5-HTTLPR polymorphism is particularly well studied in the context of interactions between genes and the environement. 
• the interaction between child maltreatment and S allele of the 5-HTTLPR was found to predict depression in maltreated children 

• Rhesus macaques were studied that were either homozygous for the long 5HTTLPR variant (l/l) or heterozygous for the short and long form (l/s). 
• mother reared and nursery-reared monkeys were assessed on days 7. 14. 21 and 30 of life on a standardized neurobehavioural test. 
• Both mother-reared and nursery-reared heterozygote animals demonstrated increased affective responding relative to l/l homozygotes
• Nursery reared, but not mother reared l/s infants exhibited lower orientation scores than their M counterparts. 
• The results demonstrate the contributions of rearing environment and genetic background, and their interaction. 
• The results are comparable to those observed in human infants. Rhesus infants carrying the s allele were more distressed during the examination. In human infants, similar results have been noted at 2 months of age, where posession of an s allele results in decresed orientation scores. Here, similar results are noted, but for nursery-reared infants only.

Matt notes

• diathesis means disposition
• some individuals more prone to adverse environment due to a dispositional vulnerability (e.g. risky genes)
• children with vulnerable genotype and exposure to adverse environment will have negative outcomes
• if the environment is not negative though, outcome will be neutral.
• Two meta analyses found no evidence of GxE interaction on depression (Munafo et al, 2009 and Risch et al, 2009); however, a further, larger meta-analysis by Karg et al (2011) showed positive evidence for s significant effect involving 5-HTTLPR on depression 

Bogdan et al (2013)

• Looked at children aged 3-5.
• A 5-HTTLPR x Stressful Life Events (SLE) interaction emerged
•  ^ childresn homozygous for the short allele were more susceptible to depression in the context of elevated SLE than long allele carriers. In contrast, at low SLE exposure, short allele homozygotes had fewer depressive symptoms. 
• children homozygous for the short allele were more susceptible to the depressogenic eggects of SLE, but benefitted in the form of reduced depressive symptoms in relatively low SLE exposure. 

Matt notes:

• Things like 5-HTTLPR are highly prevalent so its in the gene pool for a reason. 
• Genes do moderate the influence of the environment on phenotype however - genetic polymorphism is not about risk per se, but susceptibility to the environment, whether good or bad.
• This is called developmental plasticity
• Theory predicts that genetically sensitive individuals will have poorer outcomes when the environment is negative BUT will also have better outcomes when the environment in positive.
• It's thought to include the model "Biological Sensitivity to Context" which has been subsumed into Differential Susceptibility. 

• Attention Bias Modification (ABM) procedures have been shown to modify biased attention with important implications for emotional vulnerability and resilience. 
• ABM procedure was used and ppts randomly assigned to one of two training groups
• One received ABM procedure designed to induce a bias in attention toward negative material, while the other was trained toward positive pictures.  
• Individuals with low and high expressing forms of 5-HTTLPR were compared
• Those with a low expression form developed stronger biases for both negative and positive pictures relative to those with the high expression.
• allelic variation in 5-HTTLPR gene predicts different degrees of sensitivity to ABM.  Variations on this genotype may determine who will benefit most (and least) from therapeutic interventions, adversity, and supportive environments.  

Matt notes:

• opposite of diathesis stress. If you have a positive environment, you'll flourish, but if there's a negative environment, you'll be neutral 
• logical complement to diathesis-stress
• genetic variation predisposes children to certain positive outcomes 
• concerned with the "bright side" outcomes only

• controlled trial in South Africa
• intervention was designed to enhance maternal-infant attachment (compared to a control group)
• carrying at least one short allelle of the serotonin transporter gene was associated with a 26% higher rate of attachment security relative to controls
• ^ but negligible difference between intervention and control group for those carrying only the long allele
• when infant genotype for serotonin transporter polymorphism was taken into account, the effect size of a maternal-infant attachment intervention targeting impoverished pregnant women increased more than 2.5 fold when only short allele carriers were considered and decreased 10 fol when only those carrying two copies of the long allele were considered

DIATHESIS STRESS

• for-worse or "dark side" outcome only

VANTAGE SENSITIVITY

• for-better or "bright side" outcomes only

DIFFERENTIAL SUSCEPTIBILITY

• focuses on individual differences in developmental plasticity - for better and for worse