Alzheimers And Down Syndrome
Down syndrome may give researchers hints at how the 21st chromosome affects the development of Alzheimers disease.
In Down syndrome, an individual has an extra copy of chromosome 21. This 43rd chromosome overall leads to symptoms, such as a flattened facial appearance, slant eyes, short neck, small ears, small hands and feet, and intellectual and/or developmental problems.
Moreover, individuals with Down syndrome develop Alzheimers at a much higher rate than the rest of the population, and at a much younger age.
Since Down syndrome seems to increase risk of Alzheimers disease, scientists believe the APP gene, which is present on chromosome 21, playsa major role in Alzheimers development.
Dementia And Down Syndrome
People with Down syndrome are born with an extra piece of DNA. This means they also have an extra copy of the APP gene. This leads to the build-up of amyloid plaques in the brain, which play a role in the development of Alzheimers disease. While not everyone with Down syndrome will go on to develop symptoms of Alzheimers, most people with the condition over the age of 40 will have amyloid build-up. It is estimated that about 50% of people with Down syndrome develop symptoms like memory loss, usually in their 50s and 60s.
To find out more about Down syndrome and dementia you can contact Downs Syndrome Association helpline on 0333 1212 300 or visit their website www.downs-syndrome.org.uk.
How Do Genes Increase Alzheimers Risk
While detecting new genes with Alzheimers links can make a big news story, about five out of every one hundred cases are attributed to ourgenetics.
Alzheimers is characterized by the deposition ofamyloid plaques andtau neurofibrillary tangles in the brain. Some of our genes, or gene mutations, are involved in development and clearance of amyloid plaques. Carrying these genetic markers increases the risk of developing Alzheimers. These include PSEN1and variations onTREM2.
Does this mean Alzheimers is genetic? Not quite: The roles of amyloid and tau in Alzheimers disease are still shrouded in mystery. And complicating things further, in the other 95 percent of cases, genes dont drive the disease. They may be part of the story, but their interactions with other aspects of our biology, aging, and the environment are all in play.
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The Five Percent: Strong Genetic Determinants Of Alzheimers
There are a few genes that almost certainly will lead to the development of Alzheimers. These genes are responsible for about five percent of all cases. All these genetic perpetrators happen to increase the production of amyloid plaques a key Alzheimers biomarker early in life:
In most people, these genes will lead to an early-onset Alzheimers between a persons late 30s or early 60s. But do these early-onset genes tell us about the underlying cause of Alzheimers at large? Scientists still arent quite sure.
The tricky part is: There are plenty of people who do develop Alzheimers, but whodont develop this key biomarker of amyloid plaques. Meanwhile, some people with amyloid plaques dont ever develop the disease, making the link between amyloid and Alzheimers tenuous.Some scientists believe that the biology of early-onset Alzheimers may involve a different mechanism, other than amyloid, altogether.
So, while there are a few genes that almost certainly will lead to the development of Alzheimers, unfortunately that doesnt solve the mystery of whats behind the other 95 percent of cases.
Genetic Testing For Dementia
An individual can undergo genetic testing for dementia, but it is expensive and not always accurate.
The tests look for specific mutations involved in the condition. However, the tests cannot detect all possible causes of dementia. For example, experts estimate that 1% or fewer cases of Alzheimers disease are due to a specific mutation in certain genes. In other cases, the cause is unknown or multiple factors are involved.
Additionally, someone may have a certain mutation but never develop dementia. Therefore, doctors may not recommend genetic testing for dementia as a routine screening tool.
Genetic testing can be useful in families with a known genetic mutation for the disease. Tests can show which family members have the mutation and may develop Alzheimers disease.
If someone is considering genetic testing, they should first discuss their options with a doctor and/or a genetic counselor. The person should be fully aware of what the results of the test can mean before undergoing it.
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Genes That May Influence Alzheimers
The above-linked Alzheimers Society article is informed by responses from Professor Nick Fox, Honorary Consultant Neurologist at the Institute of Neurology in London. The article tells us:
- 99% of Alzheimers cases are not hereditary. And since the most significant risk factor is age, its not uncommon to have a parent or grandparent with Alzheimers disease who is in their late 70s and 80s. In that same 99% of Alzheimers cases, your risk of inheriting of Alzheimers compared to the rest of the population is very slight.
- In less than 1% of all Alzheimers cases, there is a very rare type that is hereditary. Early-onset Familial Alzheimers Disease, , described here and here, affects between 2-3% of the population. If a physician diagnoses you with eFAD, one of your parents will have had the disease if they lived long enough. In addition, your siblings and children may have a 50-50 chance of inheriting eFAD. Note that early-onset Alzheimers usually occurs in individuals who are in their 30s, 40s or 50s. In rare cases, it occurs when a person is in their 20s.
- Researchers have discovered that certain genes will cause early-onset Familial Alzheimers Disease if they have a specific kind of mutation or change. Known as PS1, PS2 and APP, the full names of these genes are: Amyloid precursor protein gene APP on chromosome 21 Presenilin 1 on chromosome 14 and presenilin 2 on chromosome 1.
Genes And Late Onset Alzheimers Disease
Late onset Alzheimers disease affects people over the age of 65. It is the most common type of Alzheimers and is likely to be caused by a combination of risk factors including our age, lifetsyle and environment. Our genetics also play a part.
To date, scientists have found versions of over twenty different genes that are associated with an altered risk of developing Alzheimers disease. However, having one of these versions may only have a small effect on our total risk. There is still a lot to be understood about these genes and their role in the development of late onset Alzheimers.
The most well known gene with the largest effect on our risk is called APOE. This gene makes a protein that helps keep our brain cells healthy. There are three different versions of it APOE2, APOE3 and APOE4 and we inherit one version of the APOE gene from each parent.
People who inherit one copy of APOE4 are around three times more likely to develop Alzheimers disease. About one in fifty people inherit two copies of APOE4 one from each parent. They may be more than eight times more likely to develop Alzheimers. However, due to other contributing factors, such as age and lifestyle, people who inherit APOE4 still may never develop the disease.
More information about young onset Alzheimers disease can be found here.
Is genetic testing available for young onset Alzheimers?
You can read a personal account about deciding to be tested for a gene mutation on our blog here.
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Reducing Your Risk Of Developing Dementia
As mentioned earlier, genes increase the risk of dementia but do not cause it in most cases. There are multiple risk factors associated with dementia, including cardiovascular diseases, diabetes, and smoking, that can be managed to help in preventing dementia. Maintaining a healthy lifestyle with physical exercise, a balanced Mediterranean diet, low levels of alcohol intake and abstinence from smoking can help in reducing the risk of dementia.
Individuals with substance use disorders are often at an increased risk of developing dementia. In addition, family members of an individual with dementia may turn to substances to deal with the stress of caring for their loved one. If you or a loved one suffers from a substance use disorder, The Recovery Village can help. Contact us today to learn about specialized treatment programs that can work well for your situation.
Should I Get Tested For Apoe
Youve probably seen the ads for genetic test kits that can not only find your long-lost cousins, but can also tell you what your risk is for certain diseases. While these testsboth the ones you do at home and the ones you undergo at a medical centercan detect the presence of the APOE-e4 gene, they cannot predict whether or not you will develop Alzheimers. This is why so many experts and advocacy groups, including the Alzheimers Association, advise consumers to only undergo genetic testing only after very careful consideration, and with the guidance of a genetics counselor who can put the risk in perspective.
The decision to get tested is highly personal, but its important to understand the implications, says Dr. Noble. You have to ask yourself, what are you going to do with the information? What are the possible positive and negative implications? How will this affect other people in my family? Dr. Noble points out that while it is illegal for medical insurance companies to discriminate based on genetic testing, thanks to the Genetic Information Nondiscrimination Act of 2008, that law does not apply to long-term care insurance or disability insuranceso it is possible that your results may affect your ability to get coverage for your care if you should become disabled.
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The Recipe Book: Apoe4 And Other Risk Genes
The human genome is like a book of recipes, with each of our 20,000 or so genes serving as a guide to make a specific dish. In some peoples genomes, slight variations in these recipes exist.
Thanks to advances in sequencing technology, we can read the recipe book. So far, however, we do not fully understand each section. Our cells first copy the instructions within the master recipe book before passing on these instructions to their sous chefs who make the dish .
To carry the recipe metaphor further, foods like pufferfish, shark meat, or even rhubarb need to be specially prepared so that they do not poison the eater. Similarly, a small change in the genetic code could make what should be a regular protein damaging or cause it to disrupt an important process.
By far,ApoE4 is the most prominent example of a recipe gone wrong genetic risk factor. Carrying one copy of the gene is known to increase the risk of developing Alzheimers, at least in white populations, up to three times, while carrying two copies may increase the risk up to twelve times. If the chefs instructions to the sous chef are wrong, then the final dish wont come out right in some cases like with ApoE4 the mistake sometimes ruins the dish. However, knowing this risk factor hasnt led to any treatments focused on the gene.
Other Alzheimers Risk Factors
In addition to genetics, ones risk of developing Alzheimers may be affected by other factors, including:
- Head injuries According to the Alzheimers Association, experiencing a head injury has been linked with an increased risk of developing dementia. They recommend wearing seatbelts and helmets, and taking steps to fall-proof your home.
- Gender While there hasnt been a direct link between ones gender and their Alzheimers risk, men are more likely to engage in behaviors that could increase their chances of developing the disease. Women live longer than men, which contribute to their risk of developing the disease.
- Heart health Ones risk of developing Alzheimers or vascular dementia may be increased by conditions like heart disease, diabetes and stroke. High blood pressure and cholesterol levels have also been linked to Alzheimers, according to the Alzheimers Association. The Alzheimers Society says heart-hurting habits like smoking can also increase your risk.
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Alzheimers And Genetics: Understanding The Risks
The genes we inherit from our parents help determine everything from our height to the color of our eyes. According to The Fisher Center for Alzheimers Research Foundation, they may also affect whether we develop diseases like Alzheimers.There are two types of Alzheimers disease:
- Early-onset, which affects people between the ages of 30 and 60
- Late-onset, which may occur at age 60 or older
Diagnoses of early-onset Alzheimers disease are extremely rare. Only 10% of people living with the disease developed it before the age of 60, according to the National Institutes of Health.
When it comes to genetics, there are three gene variations that affect our risk of developing this form of Alzheimers:
- Amyloid precursor protein on chromosome 21
- Presenilin 1 on chromosome 14
- Presenilin 2 on chromosome 1
If your mother or father carries one of these three gene variations, theres a 50/50 chance youll inherit it. If you do, there is a very strong probability you will experience symptoms of early-onset Alzheimers, says the National Institutes of Health.
As for late-onset Alzheimers and genetics, the research is even more unclear.
Your Risk Of Dementia: Do Lifestyle And Genetics Matter
- By Chirag Patel, PhD, Contributor
Globally, Alzheimers disease and other forms of dementia are a major burden on individuals and communities. To make matters worse, there are few treatments to combat these complex illnesses. Even the causes of dementia are widely debated. Sadly, clinical trials for drugs to stop or even slow its progress have come up short. Taking a different tack, some experts hope to intervene before people are diagnosed with dementia by encouraging lifestyle changes.
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Is Alzheimers Hereditary
As you begin to age there are some things that are natural and unavoidable. This could be loss of hair and hearing, but Alzheimers is not one of the normal aspects of aging. Alzheimers is a distinct type of dementia that involves the memory and capacity to think correctly. In many people suffering from Alzheimers it also begins to cause behavior problems as well. This disease only gets worse over time and it is often gradual. The cause is not completely known, but heredity is shown to play a part.
Who Is At Most Risk
Genetics plays a role, so a person with the 4 variant in the APOE gene has a higher likelihood of developing late-onset Alzheimers, but other non-genetic factors are also associated with higher or lower risk. And many of these factors are interrelated diet, exercise, and heart health, for instance.
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Which Genes Increase Your Risk For Alzheimers
There are several genes that researchers believe have an impact on your risk of developing Alzheimers. Again, these genes do not determine whether you will actually get Alzheimers, they simply tilt the odds in one direction. The most well-known and well-studied of these risk genes is the APOE-e4 gene its estimated that 40 to 65% of people diagnosed with Alzheimers have this gene.
Everyone inherits one APOE gene from each of their parents, but there are three different alleles of the gene, including e2, e3, and e4. If you inherit one APOE-e4, you have a threefold increased risk for developing Alzheimersinherit two and it increases up to 8 to 10 times .
On the other hand, if you inherit the APOE-e2 version, your Alzheimers risk goes down. The most common APOE allelee3is believed to have no effect at all on the risk of Alzheimers. There are many other factors, including socioeconomic determinants of health, associated with the expression of the APOE gene, including race, says Dr. Noble: We know from many studies that e4 seems to have a higher risk of expressing Alzheimers in non-Hispanic white people, while it appears to have a lower impact on those who are non-Hispanic Black people, he explains.
What Is Alzheimers Disease
Alzheimers disease damages your brain, gradually destroying memory and thinking skills. Researchers believe that the damage begins up to a decade before symptoms appear. Abnormal deposits of proteins form hard plaques and tangles throughout the brain. These deposits interfere with normal brain function.
As they grow, plaques can interrupt communication between neurons, the messengers in your brain. Eventually these neurons die, damaging your brain so much that parts of it begin to shrink.
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How Is Alzheimers Disease Diagnosed
If you are concerned about symptoms, its important to talk to your doctor or healthcare professional. As part of its Healthy Brain Initiative, the CDC emphasizes the importance of early detection, which gives people and their healthcare providers information, care, and support for their diagnosis.
According to the CDC, people are typically not aware that they have the condition through much later. Its only when symptoms become increasingly disruptive, for instance when someone gets lost in a familiar place, that leads to the condition first getting diagnosed.
A doctor evaluating someone with early signs of Alzheimers disease may do cognitive tests and then refer them to a specialist for further testing. Some of those additional tests may include brain imaging and/or lab tests to look for signs of the disease, which can include structural changes in the brain or changes in levels of certain types of proteins.
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That plague on the family tree stirs dread among the next generation of Chastains but it also has inspired Lowmans daughters to rally their relatives to participate in Emorys research.
We were told in our lifetime we might not have the answer or a cure, said Dunn, who is 58. But were thinking about our children and grandchildren.
The Chastain familys DNA gives scientists perhaps their best shot at finding the genetic origins of late-onset Alzheimers, a goal that has eluded them for decades.
Researchers have found gene mutations strongly linked to early-onset Alzheimers, in part by studying a large Colombian family with hundreds of affected individuals its symptoms start when people are in their 40s and 50s. But no such gene has been found for the disease that strikes after age 65 which accounts for more than 90 percent of cases.
A gene called APOE-e4 modestly increases the risk of late-onset Alzheimers in some people, but it isnt enough by itself to cause disease. Instead, the risk seems to come from a complicated combination of gene variants, or mutations.
If we can identify a new gene, it could have profound impact on understanding the disease, said Levey, a neurologist and director of Emorys Alzheimers Disease Research Center. Genetic sequencing of the Chastains has identified some promising targets, but has not yet produced a pivotal result, he said.
If we can identify a new gene, it could have profound impact on understanding the disease.
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