Recent Developments in Alzheimer's Disease: Vaccination and Genetic Screening. |
Created March 3rd, 2002. Copyright 2002 by Duane Hewitt
Other
Articles.
Back to Main Page.
Vaccines have a long history for treating infectious diseases. In 1796 Edward
Jenner developed the smallpox vaccine from the observation that milkmaids exposed
to cowpox were immune to subsequent smallpox infection. The vaccine led to the
eradication of smallpox by 1980 and the disease now only survives by official reports
in samples held in the United States and Russia. Vaccines have been employed in
the prevention of many diseases.
The basic principle behind a vaccine is that the immune system is effective
in responding to foreign substances that have been encountered previously. To take
advantage of this memory of the immune system a vaccine stimulates the production of
antibodies with pieces of the bacteria or viruses that cause a disease. Therefore when
the actual disease is encountered the immune system is prepared to react and prevent the
disease from taking hold in the immunized person.
Alzheimer's disease is a neurodegenerative disorder that is the most common
cause of mid to late life dementia. The onset is gradual with clinical symptoms appearing
usually between the ages of 60-70. It is estimated that 10% of individuals over age 65 and
40% of people over age 80 are afflicted with Alzheimer's disease. With the age 85 and older
group being the most rapidly growing demographic segment Alzheimer's disease will become a
very serious public health issue over the next several decades. In fifty years as many as
one hundred million people worldwide may be suffering from this dementia. Therefore
Alzheimer's disease has become a major focal point for neuroscience research.
The progression of Alzheimer's disease is often accompanied by changes in
behavior and personality.
There are mutations that have been shown to be associated with early onset
of Alzheimer's disease. Families have been found where these mutations may cause Alzheimer's
disease to manifest itself in the victim's thirties. These genes are dominant which means that
if you have one bad copy from your parents then you will probably develop the disease. There are
also milder mutations that are known to be associated with increased risk but do not guarantee
that Alzheimer's will develop.
There are two major disease asssociated phenomena that develop in Alzheimer's
brains. They are called amyloid plaques and neurofibrillary tangles. Amyloid plaques are
accumulations of Beta-amyloid protein outside neurons in the brain. The neurofibrillary tangles
are damage that occurs within neurons and impair the function of these cells. Both the tangles
and the plaques are involved in the progression of Alzheimer's disease but the precise mechanisms
have not been defined. I will delve into the molecular mechanisms of Alzheimer's disease more
deeply in a future article. Currently there are not any drugs that halt the progression of this
disease the only drugs that do exist alleviate the symptoms but do not treat the underlying causes
of Alzheimer's disease.
Recently the scope of vaccines has been expanded beyond infectious diseases to
the area of cancer. Cancer vaccines are an attempt to recruit the immune system to attack cancerous
cells just as a smallpox vaccine enables the immune system to negate the smallpox virus. Now
several groups have embarked on developing vaccines for Alzheimer's disease with some promising
results in animal models.
Mouse models have shown that vaccinations cause an immune response that blocks
accumulation of Beta-amyloid plaques. The initial human clinical test subjects displayed an immune
response to Beta-amyloid. However the trials have been recently discontinued because several patients
developed inflammation of the brain. There are alternative vaccines and therapies under development
so it remains to be seen how serious this setback is for the prospects of an effective treatment for
Alzheimer's disease.
In a recent development related to Alzheimer's disease a baby was pre-screened
so that she would not inherit early onset Alzheimer's disease. The mother was known to be a carrier
and she will develop Alzheimer's in her thirties. Under normal circumstances the child would have
stood a 50% chance of receiving the disease causing gene from her mother. However, through the use
of in vitro fertilization techniques eggs were selected and fertilized that did not carry the
disease gene.
The baby is free of the early onset Alzheimer's mutation but sadly her mother
will likely develop Alzheimer's by the time that she is a teenager. However she has left her the
wonderful legacy of freedom from the same fate. This example shows that inherited diseases can be
screened and eliminated in children for a couple thousand dollars. In my mind this seems to be a small
price to pay. This case has caused a stir amongst medical ethicists who are sounding the alarm bells
about designer children. However in this case I do not see any compelling arguments against this use of
this technology. My grandfather suffered from Alzheimer's disease and I would not wish this suffering
upon anyone.