It has long been known and assumed that many mental disorders have a heritable component. However, less research has been done on whether children are also at greater risk of suffering from mental disorders other than those of their parents. Recently published in the journal World Psychiatry, led by Hospital Clínic-IDIBAPS together with King's College London (UK) and Dalhousie University (Canada), is the largest meta-analysis to have studied this issue to date.
After pooling 211 studies involving more than 3 million children of parents with mental disorders and more than 20 million people as a control population, the researchers conclude that children of parents with such conditions (at least one of the two) have more than twice the overall risk of developing some kind of disorder, not just the one their parents have. In terms of absolute risk, children of parents with bipolar, depressive or anxiety disorders, for example, are more than 50% more likely to have some kind of disorder during their lifetime.
According to the authors, these data can be used to improve personalised prevention and even to incorporate them into genetic counselling for couples with mental disorders. To explain the details of the research, the Science Media Centre Spain organised an informative session with Joaquim Raduà, psychiatrist and head of the "Imaging of mood and anxiety disorders" research group at IDIBAPS, who was one of the co-authors of the study.
There are many studies that look at the risk that a son or daughter of a person with a mental disorder will also develop it, but there are fewer studies that analyze the risk of developing other different disorders
Joaquim Raduà
"There are many studies that look at the risk of a son or daughter of a person with a certain mental disorder also developing it, but there are fewer studies that analyse the risk of them developing other different mental disorders," explained Raduà. "We don't just look at one diagnosis, but at the whole range of diagnoses that have been studied. This information is very important for prevention, because what is really effective in reducing risk is selective and proportional prevention. If it is done indiscriminately, it can even be harmful," he said.
The published analysis indicates that the risk of having the same type of mental disorder as the parents is multiplied by three times overall and by just over two times if all the diagnoses included are considered. According to the authors, the risk of developing a disorder if either parent has a mental disorder is 55%. However, Raduá acknowledges that this last figure "is not one of the strongest in the analysis, because it is based on few studies. Moreover, it should be borne in mind that 1 in 6 people without affected parents develop a disorder during their lifetime".
Raduà also pointed out that general risk is not the same as individual risk. Mental disorders are often due to multiple causes and the study does not allow us to differentiate between heredity due to genetics and heredity due to environment. There are many factors that can increase or decrease the risk, such as the consumption of toxic substances, physical exercise or others considered to be more social, such as those derived from racism, work-related stress, bullying, etc.
The information from the analysis, however, could be incorporated into genetic counselling, Raduà said. "But not in a fatalistic way, because the idea is that environmental factors are also very important, that there is a part that we can control. That allows us to empower people," he reasoned.
Reactions from other experts
On the other hand, SMC Spain has also sought independent opinions on the study from other experts who were not involved in the study. For Alberto Ortiz Lobo, psychiatrist at the Carlos III Day Hospital - Hospital Universitario La Paz (Madrid), "epidemiological studies in psychiatry are very controversial. The diagnoses of mental disorders are made with very soft data [and] the study follows the same line of inflation of diagnoses and imprecision in their determination".
Ortiz Lobo adds: "These imprecise figures do not allow us to consider any genetic counselling as the authors seem to suggest (...). The primary prevention in mental health proposed by the WHO is to establish policies that act on the social determinants associated with serious mental disorders such as child abuse (whether due to neglect, physical, sexual or psychological abuse, parental loss, bullying by peers...), low levels of education, violence, war, discrimination, substandard housing, etc.".
For his part, Javier Costas, lead researcher of the Psychiatric Genetics group at the Health Research Institute of Santiago de Compostela (IDIS), "for the last decade it has become clear that part of the genetic susceptibility to suffer from a mental disorder is shared between different disorders. Similarly, part of the environmental factors are risk factors for different disorders. Therefore, the question arises as to whether a person with a parent with a specific mental disorder also has a higher risk of suffering from a different mental disorder.
The work is an update on a topic of clinical relevance, which implies a great effort to synthesize the large amount of existing information
Javier Costas
According to the researcher, "the work is an update on a topic of clinical relevance, which involves a great effort to synthesise the large amount of existing information. It provides updated risk estimates, although, in general, they are not very precise (...). The authors decide to give equal weight to two types of studies. A different weighting would lead to different results (...). The work is published in a prestigious journal, the official journal of the World Psychiatric Association. It will therefore have an impact on the perception of psychiatric diagnoses not as watertight entities, but as entities without clear boundaries and sharing causality, with the clinical consequences that this implies".
