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Study Shows Impact of Parkinson's Gene

Even a single mutated copy can speed symptoms

WEDNESDAY, June 14, 2006 (HealthDay News) -- Researchers report that inheriting even one copy of a mutated gene known to cause Parkinson's disease might trigger early symptoms.

The parkin gene -- already known to hasten the age at which Parkinson's symptoms appear -- was previously linked to early-onset Parkinson's when two copies of the mutant gene were copied. This new study, conducted by a research team at Massachusetts General Hospital, shows that the risk increases with even one copy of the aberrant gene.

"This is the first time anyone has shown that a single parkin mutation can lower the age of onset," study author James Gusella, director of the MGH Center for Human Genetic Research, said in a prepared statement. "We don't know if that would be sufficient to cause the disease. It's more likely that these mutations increase susceptibility to other factors underlying the development of Parkinson's. The result also lets us know that future researchers shouldn't just study the effects of completely knocking out the parkin gene -- we'll need to examine knocking out a single copy as well."

The finding appears in the June issue of the Archives of Neurology.

The research team wanted to evaluate which genes are responsible for the hereditary forms of Parkinson's disease. To do so, they studied 329 families with at least two cases of Parkinson's per family from across North America, Europe and Australia.

Two types of families were studied from this group: those with siblings who have the same versions of the chromosome 6 region (where the parkin gene is found); and those with one family member whose symptoms appeared before age 54. Early onset for Parkinson's is defined as symptoms before age 50.

Patients in each family with the earliest symptoms underwent genetic screening to search for parkin mutations. If the screen was positive, the other family members with Parkinson's were also screened. Of the 183 families in this section of the study, 23 families had parkin mutations, 13 of which had at least one family member who had two mutated copies of the gene. Ten of the families had only one mutated copy of the parkin gene.

Of the population of families with parkin mutations, 43 was the average age at which symptoms began to appear. Onset began at an average age of 61 in families with identical chromosomal markers and no mutations, and about age 50 in families with one parkin gene mutation. Patients with two mutated copies of the parkin gene experienced onset at an average age of 36.

"This study reinforces the fact that there are multiple mechanisms behind Parkinson's disease, and will lead us to examine other pathways with which parkin interacts," Gusella said.

More information

To read more about Parkinson's disease, head to The National Parkinson Foundation.

SOURCES: Massachusetts General Hospital, news release, June 12, 2006
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