Monday 2 September 2013

Bad blood

Here is an interesting study, which simultaneously seems wrong and right. Wrong, because the stated risks of mental illness in offspring seem so high, and right because it soon becomes obvious that many family studies have highlighted the wrong thing: they have assumed that if a parent has a particular, individual severe mental disorder, then the main thing to look for in offspring is the same mental disorder. This limits the calculation of risk too narrowly. The better question is the one sometimes asked by patients: I have mental problems, so what is the chance that my kids will have mental problems?

Risk of Mental Illness in Offspring of Parents With Schizophrenia, Bipolar Disorder, and Major Depressive Disorder: A Meta-Analysis of Family High-Risk Studies  Daniel Rasic, Tomas Hajek, Martin Alda and Rudolf Uher

Rasic et al. give their answer thus:  1 in 2 of your children will have mental problems.

How have they got to so high a figure, when the population estimates for individual psychiatric disorders are so much lower? The authors have taken the broad category of severe mental illness (schizophrenia, bipolar disorder, and major depressive disorder) and then looked for those disorders and any other mental disorders in the offspring of parents with those disorders, compared with severe and all other mental disorders in controls, the offspring of parents without those severe mental illnesses. They have looked at 33 family high-risk studies which have investigated psychopathology in individuals who had a biological relative, most commonly a parent, with SMI. These studies have provided a wealth of information about risk of mental disorders in offspring. However, the rates of mental disorders in offspring vary across studies, and a robust overall estimate is not available. They try to correct that omission. Here are the results from their Table 2 for offspring for all ages, taken from the meta-analysis described in their paper.

Parent diagnosis          Offspring disorder (relative risk)

SMI                               SMI    2.52     Any mental disorder   1.60   

Schizophrenia              SMI     2.21     Any mental disorder   1.45

Bipolar                          SMI    2.42     Any mental disorder   1.66

Depression                   SMI     2.45     Any mental disorder   1.64


Relative risk is not a particularly friendly statistic. It can mislead, and often requires looking up its definition. Absolute risk (which they give for all disorders in Table 1)requires less explanation  The chance of getting an SMI in the general population is 12% and the chance of getting an SMI if your parent has one is 32%, which is 2.5 times higher, thus providing the relative risk estimate of 2.52. As always, there is the problem of definition as to what constitutes a psychiatric disorder, but having a parent with a major psychiatric disorder makes it two and a half times more likely that the children will get the disorder. That is a very significant increase.

To look at the total effect for the children, one has to multiply these relative risks by the frequency of each of the parent diagnoses. Since depression is more common than schizophrenia, depression adds more to the eventual risk for offspring of getting any mental disorder.

Psychologists rarely miss a chance to criticize psychiatric disorders, but here is a result which should give pause to everyone in the psycho-professions: the broad grouping of SMI seems to be more useful in social terms than the more precise individual diagnoses (it indicates that the person is significantly at risk, needs help, and will have times, often long times, when they cannot contribute much to others) and the broad category appears to have higher predictive value for children’s outcomes.

Of course, a disordered parent passes on genes and also a disordered or interrupted parenting to their child, but the overall consequence is what matters.  This study shows how a broader approach can give a better estimate of overall risks, and helps bridge the gap between family high-risk studies and population registry studies. In a nutshell, given bad blood, something of that bad blood is very likely to pass on to your children, such that one third of them may develop a mental disorder by early adulthood. Sobering, and closer to the foul mutterings of the man and woman in the street, who always regard mental problems with some alarm and prudent avoidance.


  1. "the foul mutterings of the man and woman in the street, who always regard mental problems with some alarm and prudent avoidance": but if the M&WITS are right in their caution, why are their mutterings "foul"?

  2. but here is a result which should give pause to everyone in the psycho-professions: the broad grouping of SMI seems to be more useful in social terms than the more precise individual diagnoses

    You are saying that DSM diagnoses fail to carve Nature at her joints, particularly that they are too broad. Interpreting further, that there is something like a crazy-g that is the real problem and that psychiatric disorders are just different ways that someone with a high crazy-g present to the caregiver. Am I understanding your point?

  3. a general factor of craziness. I hadn't quite thought of it that way, but yes, that is the main drift of the argument. It seems that some major mental disorders have in common the fact that they end up being transmitted to the sufferer's children, and that is a general risk factor, not one specific to each specific disorder. Psychiatry cannot help but be descriptive. It does not have an underlying rationale, other than biology. So far, the match with biological markers has been a disappointment. This finding, if confirmed, suggest that these narrow definitions of mental disorders have risk factors in common. Perhaps they have a common fragility, and circumstances are what lead to an individual fracture. So the main author argues, and I agree with his point.

  4. Thanks. I was reminded of an example, brain tumors, that Szasz used to use when making the somewhat different point I touch on below. Since what a brain tumor does to you depends on what it is pushing on, they can generate a wide variety of symptoms. Before imaging got reasonably good, it is no doubt the case that some subset of people with brain tumors were diagnosed with psychiatric disorders, and presumably there were a wide variety of such mis-diagnoses, depending on what the tumor was pushing on.

    the match with biological markers has been a disappointment

    About this, Szasz would have said that any time a biological cause is found (like with brain tumors), the condition immediately stops being in the bailiwick of psych guys and starts being in the bailiwick of neurologists, surgeons, oncologists, etc. He'd say that the lack of biological markers for psych conditions follows from the social definition of psych conditions --- we say "I'm not crazy: I have a brain tumor" a lot more often than we say "I'm crazy because I have a brain tumor," and, even when we say the latter, I think we generally mean the former.

  5. In general, psychiatric diagnoses retreat as neurology and imaging and genomics advance. Hysteria, for example, became a less frequent diagnosis as neurology improved in its methods of investigation. This might well continue, particularly if we ever find underlying genetic causes for some of the major mental disorders. However, psychologists can still argue that a lot of our responses to demonstrably physical illnesses vary according to our personalities and circumstances

  6. a general factor of craziness-

    I think that co morbidity is the rule more than the exception. And the MMPI scales create a general factor (see Irwing and Rushton).

  7. Yes. Co-morbidity should have been a clue that we didn't have a clue. And yes, I am now more in favour of a general factor of personality. See my post on intelligence, personality and self knowledge