'Broken' body clock may be linked to depression

"Depressed people are out of sync with the rest of the world because their body clocks are broken," reports the Mail Online website, while The Independent claims that depressed people live in a "different time zone".

The story comes from a study that looked at the activity of genes thought to be involved in regulating the body's internal clock – the innate sense that most people have of the changes over a 24-hour day to night cycle (circadian rhythms).

Researchers did a detailed study of gene expression, the effect that certain proteins contained inside individual genes have on genetic activities inside the body.

The study involved examining brain tissue taken from people who donated their brains to science after their deaths. Of the sample, 55 people had no history of psychiatric illness, while 34 patients had a history of severe depression (major depressive disorder, or MDD).

Researchers found that the gene activity associated with regulating circadian rhythms was much weaker, and often disrupted, in the brains of patients who had MDD.

These results possibly present, as philosophers put it, a "causality dilemma" (a chicken and egg problem) – does depression lead to a disrupted body clock, or does a disrupted body clock make people vulnerable to depression?

It is too early to say what help these findings may be in the understanding and treatment of MDD.

Where did the story come from?

The study was carried out by researchers from the University of Michigan, the University of California, Weill Cornell Medical College, Stanford University and the HudsonAlpha Institute for Biotechnology, and was supported by the Pritzker Neuropsychiatric Disorders Research Fund.

It was published in the peer-reviewed Proceedings of the National Academy of Sciences.

Both the Mail Online and The Independent covered the research uncritically. Given the specialised nature of this research, it's not surprising that both of the news stories appeared to be strongly based on an accompanying press release and were not a critical appraisal of the study itself.

What kind of research was this?

This was laboratory research using donated post-mortem brains. In it, researchers analysed in detail the gene expression of certain genes thought to be associated with circadian rhythm regulation at the time of death.

The authors point out that a common symptom of major depressive disorder is the disruption of circadian patterns, which can trigger symptoms of insomnia as well as excessive daytime sleepiness and fatigue (feeling tired all the time). However, to date there is no direct evidence of "circadian clock dysregulation" in the brains of patients with major depressive disorder.

What did the research involve?

Researchers used human brain tissue taken from a US donor programme with the consent of next of kin. They also took information from medical records, medical examiners and interviews with relatives to record the donors' previous physical health, medication use, psychiatric problems, substance use and details of death.

This was done in order to assess whether donors had a major depressive disorder, a severe form of depression that has a significant impact on day-to-day living.

They also assessed whether physiological stress at the time of death would have had an effect on gene expression, and took account of this potential confounding factor.

Researchers analysed the brain tissue of 55 donors with no history of psychiatric or neurological illness and 34 patients with major depressive disorder. Using specialist techniques called DNA microarray, they measured the expression of genes thought to be associated with regulating circadian rhythms in different areas of the brain.

They used the control group to build a detailed picture of circadian gene expression in brain tissue and compared the results with those found in the brains of people with MDD. They also used the rise and fall of the top 100 "cyclic" genes in 60 of the donors to predict the time of death in all the others, both cases and controls. 

What were the basic results?

In the brain tissue from donors without major depressive disorder, they found that the activity of "circadian" genes at certain times of the day and night was consistent with data derived from other diurnal (day-active) mammals. More than 100 genes showed "consistent cyclic patterns" over six brain regions.

However, in the brains of patients with MDD gene expression of cyclic patterns was far weaker and more disrupted, with the patients' day pattern of gene activity often resembling a night pattern.

They found that predictions of time of death were more accurate among controls than for those with MDD.

How did the researchers interpret the results?

The researchers say the results provide convincing evidence that there is a "rhythmic rise and fall" in the activity of hundreds of genes in the human brain associated with regulating the day/night cycle. There is also evidence that the activity of genes associated with circadian rhythms is abnormal in people with MDD.

The study identifies hundreds of genes in the human brain that are likely to be involved in the sleep/wake cycle. The researchers conclude that daily rhythms in these genes are "profoundly dysregulated" in MDD. They say the results pave the way for the identification of new biomarkers and treatments for mood disorders.

Conclusion

This study is of interest, but at the moment it has little bearing on our understanding and treatment of depression. It could lead to new insights and treatments in the future, but there is no guarantee that this will be the case.

Also, as the authors point out, gene activity can result from many factors, including disease and drug history. In particular, it should be pointed out that:

• the researchers relied on only 55 patients to build a "normal" picture of genetic expression associated with the sleep/wake cycle
• it is not clear whether those in the MDD group had all been formally diagnosed with MDD or how long they had had depression, and it is possible there were errors in the classification of patients either with or without MDD

In conclusion, it is too early to say whether this study's findings might help in the understanding and treatment of major depressive disorders.