May
27, 2003
Brain Tangles Occur in Normal Aging
CHICAGO ---
Accumulation of neurofibrillary tau tangles not only causes the
memory loss that occurs in Alzheimer’s disease
but also may be responsible for the memory deficits seen in normal
aging and in some cases of mild cognitive impairment, a study from
Northwestern University and the University of Miami has found.
Mild cognitive
impairment is isolated memory loss more severe than what is associated
with “normal aging,” but without
the additional cognitive difficulties or disruptions of daily living
activities characteristic of Alzheimer’s disease.
Individuals
with mild cognitive impairment have been shown to develop Alzheimer’s at a higher rate than those without cognitive
impairment, suggesting that mild cognitive impairment may represent
an intermediate stage between aging-related memory loss and Alzheimer’s
disease.
Angela L.
Guillozet, a researcher in the Cognitive Neurology and Alzheimer’s
Disease Center at Northwestern University, and colleagues reported
in the May issue of Archives of Neurology
that neurofibrillary tangles are more numerous in brain regions
associated with memory function and correlate with performance
on memory tests in cognitively normal elderly persons and those
with mild cognitive impairment.
The group’s study also showed that beta-amyloid plaques,
the other diagnostic marker for Alzheimer disease -- which some
researchers believe cause the memory-robbing neurodegeneration
that occurs in Alzheimer’s -- do not play a significant role
in cognitive status prior to the development of Alzheimer’s
disease.
The researchers investigated tangle distribution in the brain
and neuropsychological test results in five persons with no cognitive
impairment and three with mild cognitive impairment who had agreed
to donate their brain after death. The last test occurred between
15 days and a little over a year before death.
They found that individuals with mild cognitive impairment had
higher densities of neurofibrillary tangles than did nonimpaired
persons. In addition, tangle density in brain regions associated
with memory function correlated with scores on memory tests, but
density of beta-amyloid did not.
Results of
their study indicate that neurofibrillary tangles may constitute
the basis of memory loss not only in Alzheimer’s
disease but also in normal aging and mild cognitive impairment.
Further, the results seem to confirm findings from other studies
that discerned no relationship between amyloid distribution and
dementia severity in Alzheimer’s disease.
Guillozet
is postdoctoral student at the Feinberg School of Medicine at
Northwestern University. Her co-researchers at the Feinberg
School were Sandra Weintraub, professor of psychiatry and behavioral
sciences and M.-Marsel Mesulam, M.D., Ruth and Evelyn Dunbar Professor
of Psychiatry and Behavioral Sciences, professor of neurology and
director of the Cognitive Neurology and Alzheimer’s Disease
Center. Deborah C. Mash of the University of Miami School of Medicine
also contributed to the study.
This study was supported by grants from the National Institute
on Aging and from the National Institute of Neurological Disorders
and Stroke, National Institutes of Health. |