The relationship between neurodegenerative conditions such as Alzheimer’s disease and late-life mood disorders (LLMDs), including late-life depression (LLD) and late-life bipolar disorder (LLBD), is largely unexplored. Researchers in Japan quantified this association by carrying out a study in the level of tau proteins and amyloid beta (Aβ), markers of the progression of neurodegenerative conditions, in participants aged 40 years and over with LLMDs and their healthy counterparts matched on demographics.
LLMDs have a stronger association with neurogenerative dementia compared to early-onset mood disorders, which shows that distinct differences exist between the two conditions. However, the exact neurological basis of LLMDs is still largely unknown, and studies have so far only been able to suggest that an elevated Aβ and tau pathologies have been associated with LLD. This led to the rationale behind a study led by Yasuaki Mizutani and colleagues investigating whether Alzheimer’s and non-Alzheimer’s tau pathologies and Aβ positivity was associated with LLMDs, including LLD and LLBD.
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The preliminary findings from this study would suggest there is an involvement of Alzheimer’s tau pathologies in those with LLMD. GlobalData epidemiologists estimate that by the end of 2025, there will be 3.03 million total prevalent cases of Alzheimer’s in men and women aged 65 years and above in Japan; that number is expected to increase to 3.70 million by the end of 2033.
The study, published in Alzheimer’s & Dementia, recruited 52 LLMD patients from psychiatric and general hospitals in the Tokyo metropolitan area and 47 healthy controls (HCs). To erase possible confounding factors, researchers excluded those with cognitive impairment and neurological disease prior to the LLMD diagnosis. Tau and Aβ levels were detected during positron emission tomography (PET).
The results showed that the odds of being tau and Aβ PET positive were 4.8 times greater in LLMDs than in HCs; even after adjusting the LLMD cohort to those with a Mini-Mental State Examination score of 28 and higher, it also found that LLMD participants were 5.2 times more likely to be tau PET positive than their healthy counterparts from the HCs. LLMD participants were also 9.8 times more likely to be Aβ PET positive than HCs, after adjustment for the same variables. A higher percentage of both tau PET and Aβ PET was found in LLMD participants compared to HCs, 50.0% versus 14.8%, and 28.8% versus 2.1%, respectively. Additionally, LLMD participants with episodes of depression or mania had higher tau and Aβ PETpositivity (51.7% and 31.0%, respectively) compared to their non-depressive or mania counterparts (47.8% and 26.1%, respectively).
The findings from this study were significant in exploring a previously under-researched relationship, which is, the role of Aβ and tau pathologies in the manifestation of LLMD compared to those without LLMD.
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By GlobalData