What are the causes of progressive supranuclear palsy (PSP)?

We know that the symptoms of progressive supranuclear palsy (PSP) are caused by a gradual deterioration of brain cells in a few tiny but important areas at the base of the brain, in the region called the brain stem. The substantia nigra, one of these areas, is also affected in Parkinson's disease, and damage to this area accounts in part for motor symptoms that PSP and Parkinson's disease have in common.

Scientists do not know what causes these brain cells to degenerate. There is no evidence that PSP is contagious, and genetic factors have not been implicated in most individuals. No ethnic or racial groups have been affected more often than any others, and PSP is no more likely to occur in some geographic areas than in others.

There are, however, several theories about the causes of PSP. One possibility is that an unconventional virus-like agent infects the body and takes years or decades to start producing visible effects. Creutzfeldt-Jakob disease (CJD) is one disease known to be caused by such an agent. Another possibility is that random genetic mutations, of the kind that occur in all of us all the time, happen to occur in particular cells or certain genes in just the right combination to injure these cells. A third possibility is that there is exposure to some unknown chemical in the food, the air, or water, which slowly damages certain vulnerable areas of the brain. This theory stems from a clue found on the Pacific island of Guam, where a common neurological disease occurring only there and on a few neighboring islands shares some of the characteristics of PSP, Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (Lou Gehrig's disease). The cause of this common neurological disease is thought to be a dietary factor or toxic substance found only in that area.

Another possible cause of PSP is cellular damage caused by free radicals, reactive molecules produced continuously by all cells during normal metabolism. Although the body has built-in mechanisms for clearing free radicals from the system, scientists suspect that, under certain circumstances, free radicals can react with and damage other molecules. A great deal of research is directed at understanding the role of free radical damage in human diseases.

This answer is based on source information from the National Institute of Neurological Disorders and Stroke.

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