A new study reminds us that there's more to it than genes alone: Social Risk or Genetic Liability for Psychosis? The authors decided to look at adopted children, because this is one of the best ways of disentangling genes and environment.If you find that the children of people with schizophrenia are at an increased risk of schizophrenia (they are), that doesn't tell you whether the risk is due to genetics, or environment, because we share both with our parents. Only in adoption is the link between genes and environment broken.
Wicks et al looked at all of the kids born in Sweden and then adopted by another Swedish family, over several decades (births 1955-1984). To make sure genes and environment were independent, they excluded those who were adopted by their own relatives (i.e. grandparents), and those lived with their biological parents between the ages of 1 and 15. This is the kind of study you can only do in Scandinavia, because only those countries have accessible national records of adoptions and mental illness...
What happened? Here's a little graph I whipped up:
Brighter colors are adoptees at "genetic risk", defined as those with at least one biological parent who was hospitalized for a psychotic illness (including schizophrenia but also bipolar disorder.) The outcome measure was being hospitalized for a non-affective psychosis, meaning schizophrenia or similar conditions but not bipolar.As you can see, rates are much higher in those with a genetic risk, but were also higher in those adopted into a less favorable environment. Parental unemployment was worst, followed by single parenthood, which was also quite bad. Living in an apartment as opposed to a house, however, had only a tiny effect.
Genetic and environmental risk also interacted. If a biological parent was mentally ill and your adopted parents were unemployed, that was really bad news.
But hang on. Adoption studies have been criticized because children don't get adopted at random (there's a story behind every adoption, and it's rarely a happy one), and also adopting families are not picked at random - you're only allowed to adopt if you can convince the authorities that you're going to be good parents.
So they also looked at the non-adopted population, i.e. everyone else in Sweden, over the same time period. The results were surprisingly similar. The hazard ratio (increased risk) in those with parental mental illness, but no adverse circumstances, was 4.5, the same as in the adoption study, 4.7.
For environment, the ratio was 1.5 for unemployment, and slightly lower for the other two. This is a bit less than in the adoption study (2.0 for unemployment). And the two risks interacted, but much less than they did in the adoption sample.
However, one big difference was that the total lifetime rate of illness was 1.8% in the adoptees and just 0.8% in the nonadoptees, despite much higher rates of unemployment etc. in the latter. Unfortunately, the authors don't discuss this odd result. It could be that adopted children have a higher risk of psychosis for whatever reason. But it could also be an artefact: rates of adoption massively declined between 1955 and 1984, so most of the adoptees were born earlier, i.e. they're older on average. That gives them more time in which to become ill.
A few more random thoughts:
- This was Sweden. Sweden is very rich and compared to most other rich countries also very egalitarian with extremely high taxes and welfare spending. In other words, no-one in Sweden is really poor. So the effects of environment might be bigger in other countries.
- On the other hand this study may overestimate the risk due to environment, because it looked at hospitalizations, not illness per se. Supposing that poorer people are more likely to get hospitalized, this could mean that the true effect of environment on illness is lower than it appears.
- The outcome measure was hospitalization for "non-affective psychosis". Only 40% of this was diagnosed as "schizophrenia". The rest will have been some kind of similar illness which didn't meet the full criteria for schizophrenia (which are quite narrow, in particular, they require >6 months of symptoms).
- Parental bipolar disorder was counted as a family history. This does make sense because we know that bipolar disorder and schizophrenia often occur in the same families (and indeed they can be hard to tell apart, many people are diagnosed with both at different times.)
Wicks S, Hjern A, & Dalman C (2010). Social Risk or Genetic Liability for Psychosis? A Study of Children Born in Sweden and Reared by Adoptive Parents. The American journal of psychiatry PMID: 20686186
10 comments:
A more probable explanation for the elevated rate of schizophrenia among adoptees compared without controls to the general population is that parents who give children up for adoption are far more likely to be mentally ill than those who keep their children. So, this would make adoptees look worse even though it's a genetic risk.
Alternatively, the age of the child at adoption matters: if the child isn't adopted at birth, the separation from the birth parents or foster parents itself is a stressful event that can raise risk
"studying environmental factors being unfashionable."
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But only after 75 years of studying NOTHING but environmental factors, and reaching damaging and untrue conclusions about the parenting of schizophrenics.
Oh sure. And worse, the old school environmental theorists were probably interested in the wrong environmental factors. But we shouldn't throw the baby out with the bathwater.
The problem with environmental factors (and I'm thinking of the broader social factors here rather than, say, infectious causes), in medicine in general and not just in psychiatry, is that generally there's little political will to do anything about them even if you find them.
Genetic/molecular biological studies look like they could more easily be used to develop drug therapies (which are more palatable than broad social reforms) - although I'm not sure the evidence supports that contention just yet.
I would throw open a couple of items for dicussion:
Firstly, the point about the age of study subjects you mentioned. The age of onset of schizophrenia is still being debated, and I am sure that with different genetic and environmental influences it can vary widely, but first episode is more widely believed to occur during teenage/early adulthood than previously thought. And if not first episode, then at least prodromal symptoms. According to the abstract, the data was gathered in 2006? So the youngest study participants would have been 22 at time of data collection. I would suggest that throws your idea about age into question - while I agree the folks born in 1955 have way more time to get 'hospitalized' most would have been first episoders before the age of 25. Although I haven't seen the actual data - was the age of hospitalization analyzed?
I would also re-emphasize the issue of bipolar versus schizophrenia family histories and in-hospital diagnoses of psychosis. I am not sure how good the diagnoses were back in 1955 in Sweden (or anywhere), so I think this is more of a potential area of concern in the study than you stated.
In more recent years diagnostic abilities have improved: the suicidality or harm-causing behaviors of someone with bipolar I disorder are typically quite distinguishable from someone with the positive symptoms of schizophrenia (such as delusions), which is typically why either group gets hopsitalized. Survey a group of psychs and you'll find the most common diagnostic concern in BD patients is whether or not they have unipolar depression instead of bipolar.
My point simply here is that the whole study was based on hospitalization data that may or may not be accurate; not saying that there isn't an effect, or that the results are not striking, but I would be a little less skeptical of a more recent group, including separating a family history of BD from schizophrenia or autism, for example.
The WHO study should have alerted you these findings. Even you, Dirk.
OMG some of us are genetically wired to be fd up for life.
Frightening to think eugenics.. logic to world peace? I bet that's how sordids justify mass culling. Sickens me.
I bet my money too it's cheaper and easier to study genes than control for environment and maybe that's all there is to it.
Because it would be difficult to refute genetic justifications to distinguish evil and make the world a "better" place based on scientific reliables or modern day truth discursions whereas the environment encompasses costly unknowns like culture, spirituality, religion, history, changes, chemical spills, neural plasticity etc. etc. harder for govts to control let alone invest in.
This world saddens me.
Dirk, is that why schizophrenia is more prevalent than 75 years ago because they think they’ve detected the ACATTATA schizoid sequence and even if they did is it schizoid or just a peculiar shaped lipo/protein?
The easier route isn’t necessarily the progressive route.
Reiterating what others have said.. parents adopting kids from broken families should be mindful of the fact these families might not fit the physical and social expectations of certain environs perhaps due to food additives, housing, education, money, available work etc. etc. If the kid inherited the parents coping mechanisms then likely they’ll experience the same difficulties.
I blame the industrial revolution
We sometimes forget we are organic beings and no matter how much technological advancement are programmed in our minds we are susceptible to inorganic trauma. I’m not saying schizophrenia has no common underlying physical pre-disposition, but rehabilitation need not have to be identified as a helpless, no hope genetic predisposition in need of prolonged chemical consumption towards “normalcy.”
Maybe that’s the root problem for the rising misery in the youth. There’s this growing mindset of I have a disorder and need a chemical quick fix. I bet that’s what the pharmaceutical firms are quietly orchestrating, a stillborn society so eager to shed their pockets on quick fixes. It really doesn’t help pouring copious research money marketing genetic research the key to a healthier society. They can at least think outside the scope with the inclusion of all persons of society. Greedy govts!!
Someone please explain to me why divorce rates are more prevalent than 75 years ago, crime, abuse and suicide on the rise, the decline of moral standards when clearly we’ve discovered this modern day and age disorders have genetic predispositions and the drugs to alleviate such rot in society.
I'm not sure this comment is worth posting, but anyway I wonder if possibly some of the observed link between environment and mental illness might be reverse causation.
I can see how having a psychotic child can put strain on a relationship (I am assuming that adoptive parents were couples at the time of adoption as that tends to be sought by child welfare agencies). Caring for such a child could make it impractical to accept some job offers (say hard to move, hard to work long hours, uneconomical to accept a low wage job).
I only bring this up, because the data set and assumptions made by the authors can be used to see if a psychotic adoptive child increases the probability of singleness or unemployment. An instrument would be "the adoptee has a biological parent with schizofrenia or bipolar disorder."
That is, my question is are adoptive parents of people who have such a biological parent more likely to be single and/or unemployed. It's a simple calculation and the unlikely result of a statistically significant difference would imply that the authors' interpretation of the reported results is mistaken.
These are very interesting results. I would take issue with the comment in your introduction, that genetic analyses in schizophrenia have found very little so far. This is true if you are talking about so-called genome-wide association studies, which look for effects of common genetic variants. These have found very little. However, there are now a great number of very rare mutations which do predispose to schizophrenia. Many of these have been identified in just the last two years or so.
(Note that the phenotypic expression of these mutations may very well be influenced by environmental factors).
See: http://wiringthebrain.blogspot.com/2009/07/hot-news-in-genetics-of-schizophrenia.html and the following article for more details:
Rethinking the genetic architecture of schizophrenia.
Mitchell KJ, Porteous DJ.
Psychol Med. 2010 Apr 12:1-14.
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