Various mood disorders like mania, bipolar disorder and depression striking after the age of 40 may not just be mental illnesses but can precede motor or cognitive symptoms in various neurodegenerative diseases. Latest studies and growing evidences suggest that late-life mood disorders also known as LLMDs could be a warning sign for something completely different. These can pose a threat for neurogenerative diseases like dementia, even when they appear years before the actual memory loss begins to hit or any other cognitive symptoms begin to show up, researchers from National Institutes for Quantum Science and Technology (QST), Japan have claimed.

The study that was published Alzheimer's & Dementia: The Journal of the Alzheimer's Association touched upon the presence of abnormal tau protein, which is a hallmark of several neurodegenerative diseases, in the brains of 52 participants with LLMDs and 47 healthy controls. The researchers of the study also used advanced brain imaging techniques to examine all the participants and healthy controls.

A positron emission tomography (PET) scan was employed for this study that came with two different tracers. These could detect various forms of tau protein and amyloid beta accumulation. The tracers also analyzed the brain tissue samples from 208 autopsy cases to examine the exact correlation between these late-life mood symptoms and the subsequent development of neurodegenerative diseases.

The study found that 50% of the participants with LLMDs has tau accumulation in their brains as compared to only about 15% of healthy controls. Similar to this, about 29% of participants with LLMDs had detectable amyloid deposits versus just 2 per cent of controls. The autopsy results further also supported these findings and revealed a significantly higher prevalence of diverse tau protein-related pathologies in individuals who had experienced late-life mania or depression.

Dr. Shin Kurose from QST also said that, "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."