The “Missing Heritability” of Psychiatric Disorders: Elusive Genes or Non-Existent Genes?

Allostatic load in early adolescence: gene / environment contributions and relevance for mental health

Background

Allostatic load is the cumulative "wear and tear" on the body due to chronic adversity. We aimed to test poly-environmental (exposomic) and polygenic contributions to allostatic load and their combined contribution to early adolescent mental health.

Methods

We analyzed data on N = 5,035 diverse youth (mean age 12) from the Adolescent Brain Cognitive Development Study (ABCD). Using dimensionality reduction method, we calculated and overall allostatic load score (AL) using body mass index [BMI], waist circumference, blood pressure, blood glycemia, blood cholesterol, and salivary DHEA. Childhood exposomic risk was quantified using multi-level environmental exposures before age 11. Genetic risk was quantified using polygenic risk scores (PRS) for metabolic system susceptibility (type 2 diabetes [T2D]) and stress-related psychiatric disease (major depressive disorder [MDD]). We used linear mixed effects models to test main, additive, and interactive effects of exposomic and polygenic risk (independent variables) on AL (dependent variable). Mediation models tested the mediating role of AL on the pathway from exposomic and polygenic risk to youth mental health. Models adjusted for demographics and genetic principal components.

Results

We observed disparities in AL with non-Hispanic White youth having significantly lower AL compared to Hispanic and Non-Hispanic Black youth. In the diverse sample, childhood exposomic burden was associated with AL in adolescence (beta=0.25, 95%CI 0.22-0.29, P<.001). In European ancestry participants (n=2,928), polygenic risk of both T2D and depression was associated with AL (T2D-PRS beta=0.11, 95%CI 0.07-0.14, P<.001; MDD-PRS beta=0.05, 95%CI 0.02-0.09, P=.003). Both polygenic scores showed significant interaction with exposomic risk such that, with greater polygenic risk, the association between exposome and AL was stronger. AL partly mediated the pathway to youth mental health from exposomic risk and from MDD-PRS, and fully mediated the pathway from T2D-PRS.

Conclusions

AL can be quantified in youth using anthropometric and biological measures and is mapped to exposomic and polygenic risk. Main and interactive environmental and genetic effects support a diathesis-stress model. Findings suggest that both environmental and genetic risk be considered when modeling stress-related health conditions.

A developmental systems approach to executive function

According to recent claims from behavior genetics, executive function (EF) is almost entirely heritable. The implications of this claim are significant, given the importance of EF in academic, social, and psychological domains. This paper critically examines the behavior genetics approach to explaining individual differences in EF and proposes a relational developmental systems model that integrates both biological and social factors in the development of EF and the emergence of individual differences in EF. Problems inherent to behavioral genetics research are discussed, as is neuroscience research that emphasizes the plasticity of the prefrontal cortex. Empirical evidence from research on stress, social interaction, and intervention and training demonstrates that individual differences in EF are experience-dependent. Taken together, these findings challenge the claim that EF is almost entirely genetic but are consistent with an approach that considers biological differences in the context of social interaction.

The lost study: a 1998 adoption study of personality that found no genetic relationship between birthparents and their 240 adopted-away biological offspring

In 1998, Robert Plomin and his Colorado Adoption Project (CAP) colleagues published the results of a longitudinal adoption study of personality. They found an average personality test score correlation of only 0.01 between birthparents and their 240 adopted-away 16-year-old biological offspring, suggesting no genetic influences on personality. However, the researchers interpreted their results in the context of previous twin studies, produced an average 14% heritability estimate, and concluded that nonadditive genetic factors underlie personality traits. The author challenges these conclusions and notes that the near-zero correlation stands in contrast to other types of behavioral genetic methods, such as twin studies, that are more vulnerable to environmental confounds and other biases. The author shows that authoritative psychology texts frequently fail to mention this 1998 CAP study. When it is mentioned, the original researchers' conclusions are usually accepted without critical analysis. The author also assesses the results in the context of the 20-year failure to discover the genes that behavioral geneticists believe underlie personality traits. He concludes that this 1998 investigation is a "lost study" in the sense that, although it is one of the most methodologically sound behavioral genetic studies ever performed, its results are largely unknown.

Distortion, Bias, and Ethical Informed Consent: Presentations of Etiological and Treatment Factors in Abnormal Psychology Textbooks

Concerns have been made highlighting the need for true informed consent and choice when patients and/or parents are confronted with seeking treatment for severe emotional states and crises. Yet, psychosocial treatments are often derided or recommended only in conjunction with psychotropic medications because of the assumed biological basis of mental distress. At the same time, the benefits of medications are often inflated, whereas the harmful effects are drastically minimized or not reported at all. This misinformation is distributed to the public, and to patients, in part through the education of students and trainees. Early educational experiences can shape the thinking of trainees as they begin to formulate their respective approaches to clinical populations, and textbooks are a fundamental part of this education. The purpose of this study was to analyze popular abnormal psychology textbooks to evaluate their representation of the current scientific literature regarding psychopathology. Content areas that were explored were those related to depression, attention-deficit/hyperactivity disorder, and schizophrenia. Misrepresentations of the literature were pervasive in areas associated with biological findings. In addition, there were multiple omissions or biased statements related to psychosocial findings, distortions regarding the efficacy of and adverse effects of various treatments, and a lack of reports of the existence of effective alternative approaches to standard mental health care. Concerns regarding the dissemination of distorted and false information in higher education as it pertains to ethics and informed consent are discussed.