Senior Citizens’ Greatest Fear – Alzheimer’s – More
Likely if Both Parents Have It
Risk of AD increased with age – affected 31% of
those over age 60
March 10, 2008 - When it comes to disease, most
Americans fear cancer the most, but not senior citizens. Many older
people have witnessed the damage of brain-killing Alzheimer’s Disease in
a friend or relative and it has become their number one fear. New
research out today says adults whose parents - both parents - are AD
victims appear to have as high as almost four times the risk of
developing the disease.
“The majority of AD cases are late-onset, usually
developing after age 65. Late-onset AD has no known cause and shows no
obvious inheritance pattern, according to the National Institute on
Aging.
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“However, in some families, clusters of cases are
seen. Although a specific gene has not been identified as the cause of
late-onset AD, genetic factors do appear to play a role in the
development of this form of AD. Only one risk factor gene has been
identified so far.” (Read more by NIA below this news report.)
The researchers, reporting in the March issue of
Archives of Neurology, one of the JAMA/Archives journals, point out that
AD is a common cause of dementia and the leading cause of
cognitive-impairment in the U.S. elderly population.
"Because Alzheimer's disease is so common in the
general population, it is not uncommon for both spouses to develop the
disease,” they write. “Offspring of two such affected individuals would
presumably carry a higher burden of these Alzheimer's disease-associated
genes."
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Older Americans Fear Alzheimer's the Most, While
Most Adults Fear Cancer
MetLife survey finds
little planning for Alzheimer’s disease
May 31, 2006 – Most Americans fear cancer the most
and Alzheimer's disease second, but this flips for those age 55 and
older, where Alzheimer's is the disease they most fear, according to a
report issued this month - “MetLife Foundation Alzheimer’s Survey: What
America Thinks,” conducted by Harris Interactive.
Read more...
|
Suman Jayadev, M.D., of the University of
Washington, Seattle, and colleagues studied the frequency of Alzheimer's
disease in adult children of 111 families in which both parents had been
clinically diagnosed with the disease. Ages at onset of dementia were
also noted.
Of the 297 offspring who reached adulthood, 22.6
percent developed Alzheimer's disease compared with an estimated 6
percent to 13 percent of the general population.
The average age at onset for children of couples
with the illness was 66.3.
The risk of developing the disease increased with
age with 31 percent of those older than age 60 affected and 41.8 percent
of those older than age 70 affected.
"Of the 240 unaffected individuals, 189 (78.8
percent) had not yet reached age 70 years, suggesting that the incidence
of Alzheimer's disease (22.6 percent) is an underestimation of the final
incidence rate of Alzheimer's disease in this population," the authors
write.
Having additional family members with Alzheimer's
disease did not increase the risk of developing the disease, but was
associated with a younger age at onset for those who did develop the
illness.
Children with no history of the disease beyond the
parents had an older age at onset (72 years) compared with those who had
one parent with family history of the disease (60 years) or both parents
with family history of the illness (57 years).
"The role of family history and the specific genes
involved in this phenomenon require a better definition," the authors
conclude.
"Families with a significant Alzheimer's disease
history may be more likely to be referred to an Alzheimer's disease
research center and, thus, the present patients may be 'enriched' for a
particularly Alzheimer's disease-prone subgroup. Following these
families as the offspring continue to age will provide increasingly
informative data."
Editor's Note: This study was supported by grants
from the National Institute on Aging/National Institutes of Health and
by Veterans Affairs research funds.
The Genetics of Alzheimer's Disease (AD)
By the National Institute on Aging
Scientists do not yet fully understand what causes
Alzheimer's disease (AD). However, the more they learn about AD, the
more they become aware of the important function
genes* play in the development of this devastating disease.
Diseases such as cystic fibrosis, muscular
dystrophy, and Huntington's disease are single-gene disorders. If a
person inherits the gene that causes one of these disorders, he or she
will usually get the disease. AD, on the other hand, is not caused by a
single gene. More than one gene mutation can cause AD, and genes on
multiple chromosomes are involved.
The two basic types of AD are familial and
sporadic.
Familial AD (FAD) is a rare form of AD, affecting
less than 10 percent of AD patients. All FAD is early-onset, meaning the
disease develops before age 65. It is caused by gene mutations on
chromosomes 1, 14, and 21. Even if one of these mutated genes is
inherited from a parent, the person will almost always develop
early-onset AD.
This inheritance pattern is referred to as
autosomal dominant inheritance. In other words, all offspring in the
same generation have a 50/50 chance of developing FAD if one of their
parents had it.
Genes in Late-onset Disease
The majority of AD cases are late-onset, usually
developing after age 65. Late-onset AD has no known cause and shows no
obvious inheritance pattern. However, in some families, clusters of
cases are seen. Although a specific gene has not been identified as the
cause of late-onset AD, genetic factors do appear to play a role in the
development of this form of AD. Only one risk factor gene has been
identified so far.
Researchers have identified an increased risk of
developing late-onset AD related to the
apolipoprotein E gene found on chromosome 19. This gene codes for a
protein that helps carry cholesterol in the bloodstream. The APOE gene
comes in several different forms, or
alleles, but three occur most frequently: APOE e2, APOE e3, and APOE
e4.
People inherit one APOE allele from each parent.
Having one or two copies of the e4 allele increases a person's risk of
getting AD. That is, having the e4 allele is a risk factor for AD, but
it does not mean that AD is certain. Some people with two copies of the
e4 allele (the highest risk group) do not develop clinical signs of
Alzheimer's disease, while others with no e4s do. The e3 allele is the
most common form found in the general population and may play a neutral
role in AD. The rarer e2 allele appears to be associated with a lower
risk of AD. The exact degree of risk of AD for any given person cannot
be determined based on APOE status. Therefore, the APOE e4 gene is
called a risk factor gene for late-onset AD.
Scientists are looking for genetic risk factors for
late-onset AD on other chromosomes as well. They think that additional
risk factor genes may lie on regions of chromosomes 9, 10, and 12.
The National Institute on Aging (NIA) has launched
a major study to discover remaining genetic risk factors for late-onset
AD. Geneticists from the NIA's Alzheimer's Disease Centers are working
to collect genetic samples from families affected by multiple cases of
late-onset AD. Researchers are seeking large families with two or more
living relatives with late-onset AD.
Families interested in participating in this study
can contact the National Cell Repository for Alzheimer's Disease at
1-800-526-2839.
Information may also be requested through their
website,
http://ncrad.iu.edu.
>> Read more on Alzheimer’s genetics at the
National Institute on Aging
