Depression, bipolar disorder after 40 may indicate dementia risk: Study

Mood disorders like depression, bipolar disorder, or mania after the age of 40 may not be just mental health conditions but can precede motor or cognitive symptoms in various neurodegenerative diseases, according to a study on Monday.

Growing evidence suggests these late-life mood disorders (LLMDs) could be early warning signs of neurodegenerative diseases like dementia, even when they appear years before memory loss or other cognitive symptoms become apparent, said researchers from the National Institutes for Quantum Science and Technology (QST), Japan.

The study, published in Alzheimer`s & Dementia: The Journal of the Alzheimer`s Association explored the presence of abnormal tau protein — a hallmark of several neurodegenerative diseases — in the brains of 52 participants with LLMDs and 47 healthy controls.

The researchers used advanced brain imaging techniques to examine 52 participants with LLMDs and 47 healthy controls.

They employed a positron emission tomography (PET) scan using two different tracers, which can detect various forms of tau protein and amyloid beta accumulation and analysed brain tissue samples from 208 autopsy cases to examine the relationship between late-life mood symptoms and the subsequent development of neurodegenerative diseases.

They found that about 50 per cent of participants with LLMDs showed tau accumulation in their brains, compared to only about 15 per cent of healthy controls.

Similarly, nearly 29 per cent of participants with LLMDs had detectable amyloid deposits versus just 2 per cent of controls. The autopsy findings further supported these results, showing a significantly higher prevalence of diverse tau protein-related pathologies in individuals who had experienced late-life mania or depression.

“Because most of the participants with LLMDs in our study had no or mild cognitive decline, these results support the evidence that neurodegenerative diseases, including Alzheimer’s and non-Alzheimer’s tau-related pathologies, can initially manifest as psychiatric symptoms,” said Dr. Shin Kurose from QST.

Further, many participants also had tau accumulation in the frontal regions of the brain — crucial for emotional regulation and cognitive function.

The study revealed that these abnormal proteins could be detected years before traditional cognitive symptoms of dementia appeared. As revealed by the autopsy cases, mood symptoms preceded cognitive or motor symptoms by an average of 7.3 years.

Timely identification of late-life depression and bipolar disorder would allow for earlier intervention with disease-modifying treatments, the team said.

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