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Alzheimer's, Dementia & Mental Health
Researchers Uncover Genetic Clues to a Common Form
of Age-Related Dementia
Dementia with Lewy bodies is second most common after Alzheimer's
 July
17, 2006 - Researchers have found that genetic alterations originally
identified in people suffering from a rare disease may also be an
important risk factor for the second most common form of dementia among
the elderly - dementia with Lewy bodies. It is only exceeded by
Alzheimer's.
In a study recently published online in the journal
Neurology, a group from the National Human Genome Research Institute (NHGRI),
part of the National Institutes of Health (NIH), and the University of
Pennsylvania School of Medicine in Philadelphia reported that
alterations in the gene that codes for an enzyme called
glucocerebrosidase (GBA) may contribute to the development of a
relatively common neurodegenerative disease known as dementia with Lewy
bodies, or DLB.
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Lewy bodies are abnormal aggregates of protein that
develop inside nerve cells in both DLB and Parkinson’s disease.
Mutations in the GBA gene had previously been identified as the cause of
Gaucher disease, a rare, inherited metabolic disorder.
“This work shows how genetic and genomic research
involving rare diseases can help unravel the mysteries of more common
disorders,” said NHGRI Scientific Director Eric Green, M.D., Ph.D.
“Knowledge gained from studying rare diseases not
only provides insights into specific medical conditions, it also deepens
our understanding of normal cell processes and human biology in
general.”
DLB is the second most common form of age-related
dementia, exceeded only by Alzheimer’s disease. At least 5 percent of
people age 85 and older are thought to have DLB, and the condition
accounts for about one-fifth of all cases of dementia.
People affected by DLB often show symptoms of
Alzheimer’s and Parkinson’s disease, but most experts now consider DLB
to be a distinct disorder. As is the case for Alzheimer’s disease, there
currently is no good treatment for DLB.
A research group led by Ellen Sidransky, M.D., a
senior investigator in NHGRI’s Division of Intramural Research,
sequenced DNA from autopsy samples that had been carefully examined and
classified by neuropathologists at the University of Pennsylvania. Dr.
Sidransky’s group found mutations in the GBA gene in 23 percent of
patients with DLB. That rate is nearly 40 times higher than the
frequency of GBA mutations in the general population.
“Our findings are particularly significant because
this is among the first examples of a genetic change associated with
dementia with Lewy bodies. This discovery will serve to advance our
understanding of the mechanisms underlying this devastating disease,”
said Dr. Sidransky, who is also acting chief of NHGRI’s Medical Genetics
Branch.
Until recently, most research on GBA focused on
Gaucher disease, a rare, inherited metabolic disorder in which harmful
quantities of a fatty substance, called glucocerebroside, accumulate in
the spleen, liver, lungs, bone marrow and, in some cases, the brain. All
people with Gaucher disease have a deficiency of the GBA enzyme, which
is involved in the breakdown and recycling of glucocerebroside.
Over the past few years, Dr. Sidransky’s lab and
other research groups have uncovered data suggesting that GBA
alterations may also be a risk factor for the development of symptoms
that resemble those seen in Parkinson’s disease. The latest findings add
DLB to the list of disorders in which the GBA gene may play a role.
People with Gaucher disease have two mutated copies of the GBA gene,
while the DLB patients with GBA alterations have one mutated copy and
one normal copy.
“This serves as an example of how a genetic
alteration may lead to a key enzyme taking on a totally different role
from its primary function, contributing to a common, complex disorder,”
said Ozlem Goker-Alpan, M.D., the first author of the study
Specifically, the NHGRI-led group examined the GBA
gene in autopsy specimens from 75 patients who had been diagnosed with a
class of neurodegenerative disorders known as synucleinopathies, which
are characterized by abnormal aggregates of a protein called alpha-synuclein
within brain and other neural cells. The three synucleinopathies
examined in the study were DLB, Parkinson’s disease and multiple system
atrophy.
Researchers found GBA mutations in the brain tissue
of eight of the 35 cases of DLB. Only one of 28 patients with “classic”
Parkinson’s disease had a GBA alteration, while no mutations were found
among the 12 patients with multiple system atrophy.
The results may offer intriguing new avenues for
exploring the basic causes of a complex disease at the cellular level.
However, the researchers emphasized that more work and larger groups of
samples are needed to confirm these associations and determine exactly
how GBA alterations may contribute to the accumulation of alpha-synuclein
in neuronal cells.
More about study:
The NHGRI Division of Intramural Research develops
and implements technology to understand, diagnose and treat genomic and
genetic diseases. Additional information about NHGRI can be found at
www.genome.gov.
The National Institutes of Health (NIH) — The
Nation's Medical Research Agency — includes 27 Institutes and Centers
and is a component of the U.S. Department of Health and Human Services.
It is the primary federal agency for conducting and supporting basic,
clinical and translational medical research, and it investigates the
causes, treatments, and cures for both common and rare diseases. For
more information about NIH and its programs, visit
www.nih.gov.
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