Alzheimer's disease
Maria Rosa, 70, a patient with Alzheimer's disease and vascular dementia, and former business administrator, poses for a photograph at the Alzheimer Foundation in Mexico city. [Representational image]Reuters

The neurodegenerative Alzheimer's disease (AD) is being linked with reduced bone mineral density (BMD).

Less than 5 percent of Alzheimer's cases exist due to genetics, which make it difficult to detect the disorder in its early stages. Researchers have now discovered that a link between brain degeneration and bone loss exists.

Scientists are still trying to understand the incurable and unstoppable complicated changes, which take place in the brains of people with Alzheimer's disease, according to a report by NCBI. 

Researchers know that before the symptoms are discernible, tau protein and beta-amyloid get deposited in significant levels through the brain and end up killing cells by clogging them. Hence, it is important to come up with ways to detect the condition at an early stage before it causes more damage to the brain.

It has been found that Alzheimer's patients have lower BMD levels and suffer from the bone-weakening disease, osteoporosis. Bone damage takes place before dementia symptoms are detected. The mechanism linking the two is still unknown.

Bone loss is thought to be an early symptom of Alzheimer's, which is caused because of abnormal quantity of serotonin production. Serotonin chemical, produced in the brain, controls sleep and mood, and these two processes get affected in the early stage of Alzheimer's too, Medical News Today reported.

The research used genetically-altered mice called "htau". These mice were genetically changed to have human forms of the tau protein, which turns abnormal during Alzheimer's and destroys internal cell structure known as microtubules. 

The BMD of the htau mice was measured by the researchers before the development of abnormality took place in the animals. Male mice were found to have noteworthy reduction in the BMD in comparison to the normal mice.

Major changes were observed in the brain region called brainstem, which is known as the dorsal raphe nucleus (DRN), of the htau mice. The authors of the study described it as "a pivotal structure in the regulation of the adult skeleton." It was also found that the DRN secreted abundant serotonin in the brain.

An abnormal level of tau protein was also found being produced in mice aged just 4 months. The findings revealed that the depleted levels of BMD occurred before the obvious brain degeneration began in these mice. Changes in the level of the tau protein were observed in the brainstem cells of the mice. 

The authors of the study are planning to conduct further research on the molecular mechanism linking bone loss to a reduction in serotonin in earlier stages of Alzheimer's in humans.

"Measurement of bone density, which is routinely performed in the clinic, could serve as a useful biomarker for assessing Alzheimer's disease risk in our ageing population," Christine Dengler-Crish, assistant professor of pharmaceutical sciences, and anatomy and neurobiology at NEOMED, and the lead author of this study, was quoted as saying by a Science Daily report.