Head injury may increase risk of Parkinson’s

By Megan Rauscher

NEW YORK (Reuters Health) – A new study supports the
hypothesis that head injury increases the risk of Parkinson’s
disease (PD). In the study, which included twin pairs in which
one twin had PD and the other did not, head injuries of
mild-to-moderate severity were associated with a threefold
increased risk of PD developing several decades later.

“Because PD patients were matched in the study with their
unaffected twin, the study results are particularly robust, and
strongly suggest that the association is truly causal and not
just coincidental,” Dr. Samuel M. Goldman from The Parkinson’s
Institute in Sunnyvale, California noted in comments to Reuters
Health.

Head injury is an “inconsistently” reported risk factor for
PD, note Goldman and colleagues in the latest issue of Annals
of Neurology. “Because twins share many environmental and
genetic characteristics, risk factors identified in
investigations of twins discordant for PD may be less likely to
be spurious,” they further point out.

In the 93 twin pairs studied, a prior head injury with
amnesia or loss of consciousness was associated with a
3.8-increased risk for PD. Similar to other studies, there was
a long latency between head injury and PD. Head injuries
occurred, on average, more than 30 years before the development
of PD, Goldman’s team reports.

“The clinical significance of this observation is that if
an insult to the brain takes 30 years to cause clinical
disease, this means there is a lengthy period during which time
we might be able to intervene and stop or slow the degenerative
process,” Goldman said.

In the study, having two prior head injuries was associated
with greater risk for PD than having one head injury.

It’s also notable, according to the team, that the
association between head injury and PD was somewhat stronger in
genetically identical or “monozygotic” twins than in
genetically similar or “dizygotic” pairs.

In a subanalysis of 18 twin pairs in which both twins had
PD, the twin with “younger onset PD” was more likely to have
suffered a head injury. This suggests to investigators that
head injury might hasten the development of PD in susceptible
individuals.

Goldman told Reuters Health “there are many biological
reasons” through which head injury may lead to a
neurodegenerative process such as PD. “Head injury might cause
long-term inflammation in the brain,” he explained. If so,
“then the possibility to intervene would likely apply to many
types of early life environmental insults in addition to head
injury,” Goldman said.

SOURCE: Annals of Neurology July 2006.