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Alzheimer's, Dementia & Mental Health
Senior Citizens Appear to Have Exclusive Claim on
Alzheimer’s Disease
Boomers, young adults thinking they have
AD are probably wrong
 January 8, 2007 – Experts are generally agreed that
people with the APOE4 gene type are at higher risk of Alzheimer’s
disease. A new study of people of from age 24 to 64 has found, however,
that those who carry this gene do not show cognitive decline until later
years. They conclude the higher-risk genotype acts only in later years
to layer disease on top of normal aging.
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Alzheimer's, Dementia & Mental Health |
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It does not, say the Australian researchers,
contribute to cognitive change during most of adulthood. The largest
study of its kind found that carriers and non-carriers show the same
type and extent of normal age-related cognitive declines, decades before
carriers start to more often develop symptoms of dementia.
The study may help rule out the possibility of very
early Alzheimer's as the cause of the declines among carriers before
they reach old age. Write the authors, “[Alzheimer's disease] processes
may occur later in the lifespan and add to normal cognitive aging to
produce a dementia syndrome.”
The study confirmed that carriers of the APOE4 gene
type (allele, i.e. one of two or more alternative forms of a gene,
occupying the same position on paired chromosomes and controlling the
same inherited characteristic: Encarta Dictionary), which confers higher
risk for Alzheimer's, are just like other people their age throughout
most of adult life in terms of core mental functions.
Previous findings had been unclear. Lead author
Anthony Jorm, PhD, DSc, explains, “Although some areas of cognitive
decline begin from early adulthood onwards, this is not due – as some
have speculated -- to very early Alzheimer's changes in the brain.”
The APOE gene helps to transport cholesterol
through the production of apolipoprotein E. People carry two copies of
APOE, each being one of four APOE alleles. APOE4 raises Alzheimer's
risk.
In this study, researchers at the University of
Melbourne and Australian National University assessed whether the small
percentage (varying by ethnicity) of the population that carries at
least one copy of APOE4 are cognitively different from non-carriers long
before anyone shows signs of dementia.
The authors studied 6,560 people living in Canberra
or neighboring Queanbeyan enrolled in the PATH Through Life Project, a
long-term study of aging that assesses people in the age groups of
20-24, 40-44, and 60-64 years every four years for a period of 20 years.
Jorm and his colleagues evaluated whether, in each
age group, carriers of APOE4 (27 percent in their sample) were
significantly different from non-carriers on tests of functions affected
by Alzheimer's: episodic memory, working memory, mental speed, reaction
time, and reading vocabulary.
Performance on all tests (except for reading
vocabulary, which tends to hold up with age) declined across age groups,
a sign of normal cognitive aging.
However, APOE4 did not affect performance at any
age. Thus the researchers conclude that at least between ages 20 and 64,
people with APOE4 age normally in those central cognitive functions.
This finding suggests that APOE4 heightens the risk
for Alzheimer's in old age through an additional, as-yet-unknown process
that accelerates or intensifies normal changes, pushing them into the
range of disease. Jorm provides an analogy. “In general, hair becomes
thinner with age,” he says. “However, there are some people who have an
additional hereditary factor that makes them bald at an early age.”
The findings appear in the January issue of
Neuropsychology, which is published by the American Psychological
Association (APA).
About Source:
The American Psychological Association (APA), in
Washington, DC, is the largest scientific and professional organization
representing psychology in the United States and is the world’s largest
association of psychologists. APA’s membership includes more than
150,000 researchers, educators, clinicians, consultants and students.
Through its divisions in 54 subfields of psychology and affiliations
with 60 state, territorial and Canadian provincial associations, APA
works to advance psychology as a science, as a profession and as a means
of promoting human welfare.
Article: “APOE Genotype and Cognitive Functioning
in a Large Age-Stratified Population Sample;” Anthony F. Jorm, PhD, DSc,
University of Melbourne and Australian National University, and Karen A.
Mather, PhD, Peter Butterworth, PhD, Kaarin J. Ansley, PhD, Helen
Christensen, PhD, and Simon Easteal, PhD, Australian National
University; Neuropsychology, Vol 21. No. 1.
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