Individuals with bipolar disorder, which is sometimes referred to as manic depression, experience shifts in mood from feeling extremely energized and elated, to hopeless and depressed. It affects an estimated 2.6 percent of adults in the United States each year.
Recently, researchers from King's College London in the United Kingdom and the Icahn School of Medicine at Mount Sinai in New York City, NY, set out to probe this relationship further. The team were particularly interested in telomeres, which are features of chromosomes that reflect the age of an organism.
Their findings are published in the journal Neuropsychopharmacology.
Telomeres and biological aging
Telomeres act as protective caps on the ends of DNA strands. Each time a cell divides, the telomere becomes shorter, until it is so short that the cell can no longer replicate.
In this way, telomere length can be used as a measure of biological aging and susceptibility to disease. In older people, telomeres are generally shorter. However, biological aging is different from chronological aging.
Various genetic and environmental factors can influence the rate of biological aging, meaning that two people of the same chronological age might be different ages biologically.
Telomere length is currently being investigated as a biomarker for neuropsychiatric conditions. For instance, shortened telomeres have been found in individuals with major depressive disorder, schizophrenia, and dementia.
An association has also been found between telomere length and the structure of the hippocampus, which is an area of the brain involved in memory and mood regulation. Similarly, shorter telomeres are associated with reduced memory function.
Lithium reduces bipolar-related aging
For the new study, scientists took DNA samples from 63 patients with bipolar disorder, 74 first-degree relatives, and 80 unrelated healthy individuals. Relatives of individuals with bipolar disorder were included because telomere length is known to be heritable.
They found that, in the first-degree relatives, telomere length was significantly shorter than in the healthy controls. In the bipolar group, telomere length was dependent on another factor: lithium.
Lithium is a drug commonly used to treat bipolar disorder. Individuals with the condition who had taken this drug did not have significantly shorter telomeres, but those that had not taken the medication showed the same reduced length as their relatives.
This suggests that lithium prevents or minimizes the premature aging associated with bipolar disorder, backing up previous findings.
Telomere length and the hippocampus
To investigate the relationship between telomere length and brain structure, the researchers conducted MRI scans on the participants. As predicted, the team found that shorter telomeres were associated with reduced hippocampal volume.
"Our study provides the first evidence that familial risk for bipolar disorder is associated with shorter telomeres, which may explain why bipolar disorder patients are also at a greater risk for aging-related diseases."
First author Dr. Timothy Powell, King's College London
These findings are interesting in their own right, but they open up a range of new questions to be answered. Dr. Powell gives an example, asking, "For instance, do those at risk for bipolar disorder carry genes predisposing them to faster biological aging, or are they more likely to partake in environmental factors which promote aging (e.g. smoking, poor diet)? Identifying modifiable risk factors to prevent advanced aging would be a really important next step."
These findings may open up new avenues of research into new interventions. In fact, co-senior author Dr. Sophia Frangou says that the results suggest "that proteins which protect against telomere shortening may provide novel treatment targets for people with bipolar disorder and those predisposed to it."
There is much work to be done, but the links between telomeres, premature aging, and neuropsychiatric conditions are sure to yield fascinating and useful results.