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.