Adoption and family design Flashcards
What is the adoption design?
Adoption studies compare similarity for a trait in biological versus adoptive relatives to determine the degree to which genetic and shared environmental factors contribute to a phenotype.
Genetic factors are implicated if biological relatives are more highly correlated for a trait than are adoptive relatives, and shared environmental effects are implicated if adoptive and biological relatives are similarly correlated.
Perhaps more important, because they do not share genetic material, significant associations between adoptive siblings function as a “direct” estimate of shared environmental influences. Adoption studies are, thus, a particularly powerful method for the detection of shared environmental effects as compared to any other behavioral genetic design.
adoption intelligence study
– Petrill and Deater-Deckard (2004)
investigated the heritability of general cognitive ability. families included: one adoptive and one biological child of the adoptive parents. Children and mother completed an intelligence test during a home visit.
– Parent-Biological offspring correlation = .23
– Parent-Adopted offspring correlation = -0.03
– Mothers were significantly correlated with their biological children (r = 0.23) but not their adoptive children (r = -0.03). These results suggest that genetic and nonshared environmental influences are significant, whereas shared environmental influences are nonsignificant. However, adoptive children’s cognitive skills were predicted by age of placement and number of years in the home, suggesting that other nongenetic factors not related to maternal cognitive ability may be operating.
– Small sample size provides limited power to detect a difference in correlations (rP-B (.23) and rP-A (0) not significantly different)
adoption - depression study
compare to twin study
Eley et al., 1998 –
• This study included adopted children (some with adoptive siblings) and their biological and adoptive mothers, and nonadopted children (some with biological siblings) and their mothers. It therefore involves both a sibling design and a parent-offspring design and uses both parent- and self-reported depressive symptoms.
= parent-offspring results show nonshared environment is significant in predicting individual differences in children’s depressive symptoms. The shared environment may also play a role, but genetic factors do not appear to be significant in predicting individual differences in depressive symptoms in middle childhood, implying that major genetic influence on depressive symptoms is unlikely.
GOOD - Using child reports of their depressive symptoms was good as parents can only identify symptoms from overt behaviours or from what the child chooses to articulate, and thus may not recognise the presence of such feelings in their children.
BAD- Not enough power (small sample) to reject genetic hypothesis,
Results also conflict with twin study - Thapar and Mcgiffin 1994 who found that depressive symptoms in adolescents had high heritability.
These differences could be due to overestimation/underestimation of MZ and DZ in twin studies, or due to the power of the twin design to identify nonadditive genetic factors is far greater than adoption designs
Twin Design and eating disorder
Twin studies suggest moderate to high heritability (i.e., ~50%–85%) of anorexia nervosa (Klump et al., 2001)
o BUT, critics of these studies have suggested that methodological limitations constrain the conclusions that can be drawn (Bulik et al., 2000). For example, often a volunteer twin registry is used to get participants - EXPAND.
Also, many of the initial twin studies were conducted in clinically ascertained twin samples. However, there are several reasons to be cautious when interpreting twin studies of clinical samples. Clinical and community cases of bulimia nervosa differ substantially (Norman et al., 1996), The underlying genetic architecture of hospitalized cases may differ from that of cases ascertained from the general population. Moreover, if more severe forms of the disorder are likely to be referred clinically and if these are more heritable, then heritability estimates will be inflated.
Adoption study findings - eating disorders
Klump et al., 2009 – was the first adoption study to examine genetic/environmental effects for disordered eating. They compared similarity for a range of disordered eating symptoms (e.g., overall levels of disordered eating, weight preoccupation, body dissatisfaction, binge eating) in biological versus adopted female sibling pairs.
=substantial genetic effects but little to no shared environmental influences on all forms of disordered eating, significant genetic influences (59%–82%) on all forms of disordered eating, with nonshared environmental factors accounting for the remaining variance. Shared environmental factors did not contribute significantly to any disordered eating symptom.
Adoption study evaluations -eating disorders
Klump et al., 2009 -
The use of symptoms rather than diagnoses allowed for relatively greater statistical power, given that the number of siblings who would be expected to have AN or BN would be low. Moreover, continuous (rather than categorical) measures provide greater statistical power for detecting genetic effects in behavioral genetic models
The heritability estimates were similar to those found in twin studies of eating disorders (Bulik et al., 1998) and disordered eating symptoms (Klump et al., 2002). This is somewhat surprising, given that heritability estimates from adoption studies tend to be lower than those from twin studies (Burt, 2009). Nonetheless, the consistency of the results suggests that twin study findings are unlikely to be unduly influenced by limitations cited by critics and underscore the need for molecular genetic work identifying genes contributing to the genetic variance.
HOWEVER - although findings rule out the main effects of shared environment, they do not rule out interactive effects that may be equally important and potent. E.G- family conflict could interact with a nonshared environmental factor (i.e., peer group) to increase susceptibility to disordered eating in one sibling relative to another.
MOREOVER, while shared environment does not appear to be important during late adolescence/young adulthood, it may be critical during other developmental stages, like before puberty.
The study also did not assess the biological relatives of the adoptees. Their inclusion would have allowed to rule out the possibility that heritability estimates were inflated because of increased environmental similarity in biological versus adoptive siblings
Finally, they examined disordered eating symptoms rather than AN or BN per se, and examined them only in women. The findings, therefore, may not be generalizable to men or to populations of individuals with clinical eating disorders. However, our genetic and environmental estimates are highly consistent with those obtained in most twin studies of men (Tholin et al., 2005).
Limitations of adoption design
• Adoption samples may not be representative of general population, there are stringent screening processes – eg screened for psychiatric illnesses, good marital stability, and financial security. This could lead to restriction of range on rearing environmental conditions. Including more deprived families might increase impact of parental behaviour on adolescent outcomes
• Also, many children that are adopted may not be representative, there may be reasons they have been put up for adoption, eg chromosome abnormalities. This is a problem because you cannot generalise results.
• Selective placement- non-random placement in families, there could be a correlation between the genetic relatives and adoptive relatives due to agencies attempting to match the two. We could test for this by getting information on the biological parents but in many cases this information is not available. There is little evidence for selective placement however due to small amount of people adopting
Long-term effects of pre-adoption environment?
What is the Children of twins (COT) method
The children of twins (COT) design has been proposed as an alternative to the adoption study to resolve the direct nongenetic causal effects of parental treatment on child behaviour from secondary association due to the shared genetic characteristics of parents and children.
Dizygotic (DZ) twins share on average .50 of their genetic variance, whereas monozygotic (MZ) twins are unique in that they share 100% (1.00) of their genes. As a result, the offspring of MZ twins are as genetically related to their parents’ co-twin as they are to their own parent (.50). This quirk of nature or quasi-experiment gives researchers a unique opportunity to distinguish between genetic and environmental transmission from one generation to the next.
COT method - alcoohol study and evaluations of the study
Haber et al (2005)
used the presence or absence of alcohol dependence in twins (parents) to index four groups of offspring: (1) those whose parents were affected (high risk from familial factors); (2) those with an unaffected parent, but affected MZ co-twin (not exposed to parental alcoholism but at high risk from familial factors); (3) unaffected parent, affected DZ co-twin twin (not exposed to parental alcoholism but at moderate risk from familial factors); (4) unaffected parent, unaffected co-twin (not exposed to parental alcoholism and at low risk from familial factors).
=Prevalence rates for offspring conduct disorder symptoms indicated a close similarity between group 2 and the elevated rate of offspring conduct disorder symptoms in group 1.
= findings provide additional evidence for the contention that alcoholism and conduct disorder both arise, to a significant degree, from common genetic factors. Specifically, findings indicated that paternal alcoholism predicted subsequent offspring conduct disorder in the same way that it predicted offspring alcoholism.
=If environmental effects were primary, their removal should have resulted in a substantial lowering of risk for offspring conduct disorder symptoms; this did not occur. Instead, risk for group 2 offspring remained substantially elevated.
The interpretation of these findings is that genetic factors and, to a lesser degree, environmental factors both were at play in these effects. That is, although there is no evidence for a substantial environmental influence in these results, the above findings could be explained as the consequence of a small environmental effect interacting with a prominent genetic effect.
- greater statistical power would have produced a more conclusive genetic finding.
- the study sample was largely composed of intact marriages with children, more extreme forms of alcoholism, antisocial behavior, and family disruption may have been lost through divorce and/or refusal (very disturbed families participate less often in family studies) thus reducing the variability due to negative environmental influences.
COT evaulations
The CoT design only controls for the genetic and environmental characteristics of one parent and does not control for the environmental and genetic influences from the spouse of the twins (Eaves, et al 2005)
Eaves et al., 2005 therefore argue it is premature to claim that COT markedly reduces ambiguity about the causal relationships between dyadic parental treatment and offspring behavior
small datasets - As such, it is sometimes difficult to draw firm conclusions relying on the COT literature alone.
Moreover, researchers to date have focused primarily on negative phenotypes (psychopathology, negative parenting, etc.), but equally important is the investigation of positive phenotypes such as well-being, resilience, and ability.
To date, COT studies have predominantly used samples of adult twins and their adolescent or adult offspring, often employing retrospective reports to assess childhood phenotypes. However, collecting and utilizing prospective COT data could be a particularly powerful technique through which to study infant and child development as it happens.
what is a population based twin registry and how does it overcome limitations of volunteer twin registry
requires that the twins contact the investigators in response to advertisements or other forms of recruitment. There are potential biases in this sampling procedure: MZ twins tend to be overrepresented in volunteer samples and female twins are more likely to participate. Finally, individuals who are more invested in being a twin or who have strong interests in or opinions about the topic under study may be more likely to volunteer. For most purposes, the optimal strategy for twin ascertainment uses population-based twin registries. In this approach, official records (usually birth records) are used to locate all living twins
who to cite when discussing COT method?
Haber et al., 2005
CITE the people who used population based to study AN and what did they find
o Few published studies have explored genetic and environmental contributions to the etiology of anorexia nervosa in a population-based sample (Walters & Kendler, 1995). The concordance rates in MZ and DZ twins for a broad definition of anorexia nervosa were 10% and 22%. The low power attendant to this study’s sample size and the rarity of anorexia nervosa preclude conclusions regarding the contribution of genetic and environmental factors to the etiology of anorexia nervosa.
Adoption study of alcohol use and misuse - and evaluative points
McGue et al 1996 -
= problem drinking between offspring and bio parent = 0.30
=problem drinking between parent and adoptive offspring = 0.04
BUT adopted siblings correlated at 0.24, this was greater for same sex = 0.35
=Suggestive that genetic, and not familial environmental, factors mediate the relationship between parental drinking and adolescent alcohol use.
This was between mother’s and adolescent daughter’s, and between father’s and adolescent son’s only. Parent-offspring correlations for opposite-sex pairs were not significant.
= However, 24% of the variance in adolescent alcohol use and misuse is associated with environmental factors shared by adolescents growing up in the same home. Since we found no evidence that parent problem drinking or family functioning exerted a strong influence on adolescent alcohol use, they conclude that characteristics of the rearing parents are not a likely source for the shared environmental factors that influence adolescent alcohol use.
BUT this study did not assess parental drinking problems well, only used three item measure and did not distinguish between current and past drinking problems.
ALSO, the birth adolescents are atypical in that they are all being reared in a home with at least one adopted adolescent. While we do not see why birth adolescents growing up with adoptees should differ from birth adolescents growing up with nonadoptees (and indeed our results with the birth offspring sample appear to be consistent with those that others have reported), there is a clear need to extend our findings using a larger and more representative sample of birth adolescents.
However, assertive mating may in part, be responsible for the apparent shared environmental influences. Assortative mating (AM) is a process of non-random mating in which individuals select spouses based on characteristics that they and their partner share. Therefore, if individuals at increased genetic risk of developing a trait marry individuals who are also at increased genetic risk, then any children from this mating will be more likely to receive risk alleles from both parents rather than from 1 parent only, and there is an increased likelihood that the children will have 2 psychiatrically impaired parents, which can yield its own detrimental environmental and genotype-environment sequelae.
