Progressive supranuclear palsy (PSP) is caused by damage to brain cells in the parts of the brain that help control movement, balance, vision and speech.
Some of the brain cells are damaged by clumps of a protein called tau. Tau occurs naturally in the brain, but people with PSP have much higher levels.
Tau is normally broken down in the brain. In PSP the tau changes slightly, allowing clumps to build up and damage cells.
PSP has similar symptoms to another neurodegenerative condition called corticobasal degeneration (CBD), although the pattern of brain damage is slightly different. It may be the case that both PSP and CBD are in fact two related syndromes that are the result of the same underlying cause (or causes).
It is not known what leads to the overproduction of the tau protein and the resulting death of brain cells. Recent research has indicated that genetic factors can make someone more likely to develop PSP, but cases of PSP are nearly always a one-off in a family. The risk to other members of the family, including children or siblings of someone with PSP, is extremely low.
It is important to note that there is no evidence that PSP can be passed down from a parent to their child, and most experts think that it is unlikely that PSP is an inherited condition.
Further research is ongoing to identify what other factors may trigger PSP. Suggested environmental triggers include:
- an, as yet, unidentified virus or other type of infection, which may slowly infect the brain over the course of many years
- an unidentified neurotoxin (a poison that damages brain and nerve cells) that may be present in the environment
