New Video on Psychiatric Twin Studies

 A second video with Jay Joseph, this time talking about his specialty: twin studies. We focus specifically on psychiatric twin studies and discuss heritability claims. 

New YouTube Channel with Jay Joseph

 Psychologist, author and twin study skeptic Jay Joseph and I are collaborating on a YouTube channel called “Genetic Illusions.” Our first video challenges claims of a genetic mechanism for schizophrenia.

Polygenic Risk Score is Absolutely Useless for Predicting Schizophrenia

 This Study  used the best polygenic risk score (PRS) to try and predict schizophrenia for a large group of individuals. Let's just cut to the chase, here:

For all outcomes investigated, the SCZ PRS did not improve the performance of predictive models, an observation that was generally robust to divergent case ascertainment strategies and the ancestral background of the study participants.

 At this point, it is denial to believe that PRS is ever going to have any real use for schizophrenia or other classified mental disorders. The reason for this is that these traits are not related to genetic variants. The entire premise of PRS is a flawed idea for behavioral genetics. Let me add that if you let your diagnosis be influenced by polygenic scores (which you shouldn't based on this study, but you know how these go), then you will create a self-fulfilling prophecy of PRS predicting schizophrenia. 

My Review of Kathryn Paige Harden's "The Genetic Lottery "

Every few years, the scant evidence for genetic determinism will be promoted and sold in book form. In 2018, it was Robert Plomin’s “Blueprint.”  The latest comes from psychologist and behavior geneticist, Kathryn Paige Harden, with her new book: “The Genetic Lottery - Why DNA Matters for Social Equality.” From the title alone, one can see that she will be selling a version of genetic determinism with a heart. To her credit, in contrast to Plomin, Harden addresses the ramifications of behavioral genetics’ historical association with eugenics in some detail, but her book is otherwise similar in substance to Blueprint (despite her own negative review of Blueprint). Both books spin polygenic scores as a savior for the failing field of behavioral genetics, with the dubious suggestion that these results are “causal.”  

In Plomin’s case, his fanaticism for polygenic scores could be written off as wishful thinking for a man at the end of his career, touting a perceived future of ever improving polygenic prediction. Harden, on the other hand, has had a few years to see the hype dwindle, with study after study noting the limitations of such scores. 

Harden’s primary focus is what is referred to as “educational attainment,” basically a simple measurement of how far someone goes in school, viewing it as a trait with some genetic basis. In truth, this “trait” is a bit of subterfuge, serving as a proxy for intelligence, while avoiding some of the controversy surrounding genetic studies of IQ (and their association with books like Charles Murray’s, “The Bell Curve”). 

Harden's writing style at times involves condescending oversimplification through analogy: “If a gene is a recipe, then your genome -  all the DNA contained in all of your cells - is a large collection of recipes, an enormous cookbook.” This quaint presentation of the subject suggests that she is targeting a lay audience, but I question whether those not already familiar with this kind of research would find this book engaging and these analogies do not appear to clarify the subject in a more comprehensible manner.

Books of this nature generally have the same two issues to tackle and Harden’s is no exception. The first is to sell the scientific evidence related to claims of a genetic basis for educational attainment and other behavioral traits. The second relates to the ethical and practical implications of this research. I will address her treatment of both issues here, beginning with the latter.

The “Genetics” of Schizophrenia

 I have several posts on here related to schizophrenia and the claimed genetics of this psychiatric disorder and I thought it would be useful to combine twin studies, genetic studies, and polygenic scores  in one post to give some perspective. Let me start with twin studies:

During medical school and my psychiatry residency training, the genetic nature of schizophrenia was often emphasized. The strongest evidence, we were informed, was that if an identical twin was diagnosed with schizophrenia, there was a 50% chance that the other identical twin would be diagnosed with schizophrenia. While this might leave some wondering why the other 50% do not get schizophrenia with an identical genetic profile, 50% is hard to just ignore.  Well, as it turns out, it isn’t really accurate. Most of the studies that claimed such high concordance rates are from well over a half century ago. At that time, there was far more institutionalization and the diagnostic criteria were not really the same. As twin study critic Jay Joseph points out, if you take more modern studies the concordance rates are far lower, with an overall concordance rate for such studies after 1963 of 23% (some might recall a figure of 28%, but this does not include the Finnish study noted below, which seems to have been “disappeared”). 

Depending on which of these studies you examine, that 23% figure might even be a bit inflated. Take, for example, a couple of the Scandinavian studies and although I may be accused of cherry-picking, these countries tend to have better national records to draw from, which include all twin pairs and all twin pairs that are concordant for schizophrenia, so I think they arguably are more accurate. I have recently posted on these studies. One is a Finnish study from 1984 and one is a more recent Danish study from 2018. I discussed them both at more length in previous blog posts, here and here. These studies both had a full twin registry available to them and were thus able to identify all individuals diagnosed with schizophrenia, as well as any which had a monozygotic or dizygotic twin and whether they were also diagnosed with schizophrenia. The Finnish study found an 11% concordance and the Danish study found a 14.8% concordance if you look at the actual numbers. These are shocking numbers for those of us who were led to believe that it was closer to 50%.