Cortiocobasal degeneration (CBD) is caused by a progressive loss of brain cells which shrinks parts of the brain responsible for movement, speech, and the higher thought processes, such as understanding and planning.
Researchers have found that the damage is caused by a protein called tau. Tau is found in low levels in healthy brains. But in cases of CBD, the levels of tau protein increase and begin to forms into clumps which are thought to kill nearby brain cells.
CBD has similar symptoms to another neurodegenerative condition called progressive supranuclear palsy (PSP). However, in PSP the pattern of brain damage is slightly different, so it may be the case that both CBD and PSP are two related syndromes that are caused by the same underlying cause (or causes).
It is not known what leads to the over-production of the tau protein and the resulting death of brain cells.
One theory is that CBD could be the result of a genetic mutation in the gene responsible for producing the tau protein; the MAPT gene (the microtubule-associated protein tau gene).
A genetic mutation is when the instructions found in all living cells become scrambled in some way meaning that one or more of the processes in the body do not work in the way they should.
Read more about genetics.
There is evidence the genetic mutations affecting the MAPT gene are responsible for conditions with similar symptoms, such as some types of dementia and progressive supranuclear palsy.
Although, at the time of writing there is still no hard evidence to support the theory that mutations in the MAPT gene are responsible for CBD.
Also, as CBD does not run in families, it would appear that the condition is not wholly caused by the genes a person inherits from their parents.
It would seem that there are also one or more environmental factors that trigger the onset of CBD in susceptible individuals.
Possible factors could be:
- an as yet, unidentified virus, or other type of infectious agentn, which may slowly infect the brain over many years
- an unidentified neurotoxin (a poison that damages the brain and nerve cells) that may be present in the environment
