Recently I finished writing an article with child depression researcher Dr. Maria Kovacs about the concept of prodromal processes in child and adolescent depression. The article should be appearing early next year on a  special issue of the Journal of Child Psychology and Psychiatry. In that article, we reviewed the extensive literature on the predictors of childhood-onset depression and discuss how symptoms of anxiety may be a signal that a depression process may be underway. Interestingly, a paper that was just published in the same journal provides more information about this issue, and suggests that the clinical predictors of depression may actually be different for boys and girls.

In this new study, Dr. Catherine Gallerani and colleagues at Vanderbilt University were interested in examining the temporal comorbidity of depression, anxiety, conduct disorder, and substance abuse during adolescence. Specifically, depression during this time period is usually comorbid with other conditions, such as anxiety and substance abuse. Some researchers have examined the temporal relation in the onset of these disorders (what precedes what) which can provide information about which disorders increase the risk for other disorders (this follows the hypothesis that the disorders are separate entities and one makes you more likely to have another), as well which disorder signals an early phase of another disorder (this follows a prodromal view suggesting that some of these disorders may be phases of one another in that, for example, symptoms of anxiety may be an early phase of depression). In the current study, the authors wanted to examine two specific issues: how does the temporal relation between these conditions differ for boys and girls, and whether they differ between adolescents at low or high familial-risk for depression.

The study included 240 adolescents (54% female).  185 had a parent with a history of depression and 55 had parents with no history of psychiatric disorders. These children underwent psychiatric evaluations annually for 5-6 years from 6th to 12th grade.

The results:

1. As expected, children of parents with a history of depression were significantly more likely to develop depression during the study period than children at low-risk for psychopathology. In fact, at-risk children were 12 times more likely to develop depression than their low-risk peers. These at risk children were also more likely to develop anxiety (4 times), conduct disorder (11 times), and substance use disorder (6 times).

2.The temporal relation between the different conditions was affected by the sex of the child. Specifically:

2.A. There was no temporal relation between anxiety and depression for girls. However, for boys, anxiety symptoms more than doubled the risk of developing depression in the future even after controlling for familial risk. That is, across at-risk and low-risk boys, having anxiety predicted the later onset of depression.

2.B. A different pattern was observed for the association between substance abuse and depression. Substance  abuse increased the risk for developing depression by 300% among girls but not among boys. Furthermore, the odds that anxiety predicted depression among was 13 times greater for girls than for boys.

Now, what do we mean when we say “increased risk”? Does this mean that anxiety or substance use causes depression? Are we talking about true ‘mechanistic risk’ as when we say that not wearing a seat belt during a car accident increases the risk that you will be seriously injured? Not quite. In the case of the seat belt, we know the mechanism of risk. We know that not using the seat belt makes you more likely to fly through the windshield and get injured. However, in the case of the temporal association between these disorders, “increased risk” is actually a statistical term we use to refer to the possibility of observing an event in the data. For example, when looking at girls, observing a substance use disorder in the data makes us 3 times more likely that we will observe a diagnosis of depression in the same girl in the future. The data themselves do not address the possible mechanisms behind such increased risk, so we don’t quite know why the presence of one (substance use) increases the possibility of seeing the other (depression). One possibility is that indeed one causes the other – so that for example, being anxious makes you ruminate more, which in turn makes you more likely to be depressed. The other possibility is that both are symptoms of a single process, in that being anxious is simply an early symptom – or early phase – of the depression process.

Regardless of the mechanism at play however, the results are pretty compelling showing different temporal associations between these disorders and depression for boys and girls. The results suggest that we should be particularly attentive to symptoms of anxiety among boys, as these signal an increased possibility for future depression. In contrast, substance abuse among girls seems to be highly associated with future depression onset, and thus we should monitor girls that are found to abuse substances during early adolescence.

Gallerani, C., Garber, J., & Martin, N. (2009). The temporal relation between depression and comorbid psychopathology in adolescents at varied risk for depression Journal of Child Psychology and Psychiatry DOI: 10.1111/j.1469-7610.2009.02155.xResearchBlogging.org

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