According to a new research, only a small proportion of dementia cases are thought to be inherited, the cause of which is still unknown.
In a study, published in the journal Nature Communications, a team of researchers at the University of Cambridge said that they may have found an explanation for the spontaneous errors in our DNA which arise as cells divide and reproduce.
The findings suggest that for many people with neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease, the roots of their condition will trace back to their time as an embryo developing in the womb.
In common neurodegenerative diseases, toxic proteins build up in the brain, destroying brain cells and damaging brain regions, leading to symptoms including personality changes, memory loss and loss of control. Only around one in twenty patients have a family history, where genetic variants inherited from one or both parents contributes to disease risk. The cause of the majority of cases - which are thought to affect as many as one in ten people in the developed world - has remained a mystery.
Researchers hypothesised that clusters of brain cells containing spontaneous genetic errors could lead to the production of misfolded proteins with the potential to spread throughout the brain, eventually leading to neurodegenerative disease.
To test their hypothesis, the researchers examined 173 tissue samples. The samples came from 54 individual brains: 14 healthy individuals, 20 patients with Alzheimer's and 20 patients with Lewy body dementia, a common type of dementia estimated to affect more than 100,000 people in the UK.
The team used a new technique that allowed them to sequence 102 genes in the brain cells over 5,000 times. These included genes known to cause or predispose to common neurodegenerative diseases. They found 'somatic mutations' (spontaneous, rather than inherited, errors in DNA) in 27 out of the 54 brains, including both healthy and diseased brains.
Together, these findings suggest that the mutations would have arisen during the developmental phase - when the brain is still growing and changing - and the embryo is growing in the womb.
Combining their results with mathematical modelling, their findings suggest that 'islands' of brain cells containing these potentially important mutations are likely to be common in the general population.
Researchers also said that further research is needed to confirm whether the mutations are more common in patients with dementia. While it is too early to say whether this research will aid diagnosis or treatment this endorses the approach of pharmaceutical companies who are trying to develop new treatments for rare genetic forms of neurodegenerative diseases.
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