<img loading="lazy" decoding="async" class="alignright size-full wp-image-2687" title="478px-samueladamslarge" src="https://blog-api.23andme.com/wp-content/uploads/2009/01/478px-samueladamslarge.jpg" alt="" width="319" height="398" srcset="https://blogcms.23andme.com/wp-content/uploads/2009/01/478px-samueladamslarge.jpg 350w, https://blogcms.23andme.com/wp-content/uploads/2009/01/478px-samueladamslarge-240x300.jpg 240w" sizes="auto, (max-width: 319px) 100vw, 319px" />American Revolutionist and brewer Samuel Adams had one of the earliest documented cases of essential tremor.
Essential tremor causes involuntary shaking in the arms and hands, and sometimes in the neck, jaw and voice as well. Though sometimes mistaken for Parkinson’s disease, the two conditions differ in terms of cause, symptoms, treatment and outlook.
Essential tremor is not life threatening, but it can interfere with daily activities such as drinking, writing and even speaking. The NIH estimates that essential tremor affects as many as 14% of people over the age of 65.
It is suspected that a combination of environmental and genetic factors contributes to essential tremor, but so far no genetic factors have been definitively linked to the disease. Now, in a report published online yesterday by the journal <a href="https://dx.doi.org/10.1038/ng.299" target="_blank" rel="noopener">Nature Genetics</a>, researchers have identified for the first time a specific genetic variant that is significantly associated with essential tremor. Their findings connect essential tremor to a gene involved in nerve cell maintenance and survival, and could pave the way to the development of new therapeutics.
In a combined analysis of 752 subjects with essential tremor from Iceland, Austria, Germany and the United States and 15,797 controls, Stefansson et al found that the G version of rs9652490 in the LINGO1 gene is associated with increased odds of the condition.
Carrying one G increases the odds of essential tremor by 1.55 times compared to two As. The approximately 5% of the population with European ancestry with two Gs has 2.40 times increased odds.
The authors note that because of the way study subjects with essential tremor were recruited, they probably represent a more genetically-rooted, early onset form of the disease than would be seen in the population in general.
LINGO1 encodes a protein that is involved in regulating nerve cell growth, survival and specialization. Increased LINGO1 levels have been seen in people with multiple sclerosis and Parkinson’s disease. This suggests that drugs made to block the action of LINGO might be valuable for treating some diseases of the central nervous system. The authors suggest that their finding linking a change in LINGO1 to essential tremor should put this condition at the top of the list of diseases to be assessed.
“Association of essential tremor with LINGO1 opens up a new field in the research into essential tremor, and it is our hope that LINGO1 will point the way to new treatments for severe cases of the disease,” the authors conclude.

23andMe Blog

23andMe Blog Team

Study Identifies Genetic Variant Associated With Risk For Essential Tremor

<img loading="lazy" decoding="async" class="alignright size-full wp-image-2674" title="hela_hoechst_33258" src="https://blog-api.23andme.com/wp-content/uploads/2009/01/hela_hoechst_33258.jpg" alt="" width="350" height="267" srcset="https://blogcms.23andme.com/wp-content/uploads/2009/01/hela_hoechst_33258.jpg 350w, https://blogcms.23andme.com/wp-content/uploads/2009/01/hela_hoechst_33258-300x229.jpg 300w" sizes="auto, (max-width: 350px) 100vw, 350px" />
Editor&#8217;s note: We posted this a couple of years ago, but in light on the historic agreement between the family of Henrietta Lacks and National Institutes of Health, we thought it worthy of re-posting. Also read Carl Zimmer&#8217;s great piece in the <a href="https://www.nytimes.com/2013/08/08/science/after-decades-of-research-henrietta-lacks-family-is-asked-for-consent.html?ref=science&amp;_r=0http://" target="_blank" rel="noopener">New York Times</a>. The post has been slightly changed from the original.
Henrietta Lacks was only 31 years old when she died on October 4, 1951. But thanks to one of the more shameful, yet at the same time scientifically beneficial, episodes in the history of medical science, cells from the tumor that killed her grow today in laboratories all over the world.
<h6>An Aggressive Cancer</h6>
Henrietta Lacks&#8217; story is a powerful scientific and ethical lesson for researchers who work with human subjects. It all started in February 1951, when Dr. George Gey of Johns Hopkins was given a sample of cervical cancer cells that had been taken from a young African American woman who was dying of cervical cancer.
Gey wanted the cells because he was one of many scientists trying to find a way to grow human cells in for an extended period of time in the laboratory. It had been done with animal cells, but no one could get human cells to keep growing for more than a few weeks.
Ms. Lacks’ cells were different. Her tumor grew so aggressively that at her autopsy, just eight months after the cells were removed, it was found that her cancer had infiltrated her entire body.
<h6>HeLa Cells</h6>
These extraordinary growth properties, while deadly for Henrietta, were probably what brought success to Gey. He was able to keep the cells growing in a dish long-term, and he soon found himself sending samples to other scientists who wanted to study human cells, who then passed them on to their colleagues, and so on and so on.
Soon HeLa cells, as they were called (Henrietta Lacks), were everywhere and being used for everything — cancer research, drug testing, even development of the polio vaccine. The lessons learned from growing these cells also allowed scientists to coax other cells to survive in the Petri dish, ushering in a new era of biology.
But as the number of cell lines scientists had established grew, a problem emerged. It can be very difficult to distinguish two different types of cells just by looking at them under a microscope. How could a researcher know for sure which kind of cells their colleagues had sent them? How could they check to make sure they hadn’t mixed them up?
<h6>G6PD</h6>
In the late 1960s, a scientist named Stan Gartler came up with a plan.
None of the DNA technologies so commonplace today, such as SNP chips, were around back then, but scientists did know about genetic variation between people. They had observed that for certain proteins, some people made one version, while other people made a different version.
One of the variable proteins Garlter focused on was an enzyme called glucose-6-phosphate dehydrogenase (G6PD) that helps to protect cells from damage. There are two forms — A and B. The A version is primarily found in people with African ancestry. People with other ethnic backgrounds almost never have this version.
It wasn’t known then, but the two different forms of G6PD are the result of a single SNP.
(In addition to the A and B forms, there are actually other forms of the G6PD gene that cause a person to completely lack the G6PD protein. Read more in the 23andMe Carrier Status Report for G6PD deficiency. 23andMe customers can figure out whether they have type A or type B G6PD using the table at the end of this post).
<h6>Unique Cell Lines</h6>
Gartler also looked at an enzyme called phosphoglucomutase (PGM) that comes in three forms: 1, 1-2, and 2.
And now it’s time to cue the dramatic music:
Gartler was given 18 supposedly unique human cell lines by the American Type Culture Collection, a repository that scientists could order different types of cells from. One of the 18 was a vial of HeLa cells. The rest were all different types of cells, many allegedly from Caucasian people.
When Gartler tested the G6PD and PGM proteins in these 18 cell lines, he got a surprising result. All of them had the G6PD type A and PGM type 1.
There was no way this could be right. The cells from Caucasians should not have been G6PD type A. And even if all the cells had come from African Americans, it was still too much of a coincidence. In his report of his findings published in <a href="https://www.ncbi.nlm.nih.gov/pubmed/5641128?ordinalpos=5&amp;itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum" target="_blank" rel="noopener">Nature</a>, Gartler calculated that the chance of all 18 cell lines being G6PD type A and PGM type 1 was “absurdly low” — 1 in 6,000,000,000,000,000.
<h6>HeLa Cells Around the World</h6>
Every single one of the cell lines Gartler was investigating, and countless others being used around the world, had been contaminated by HeLa cells. They had taken over every Petri dish of cells they had come near.
Gartler and others sounded the alarm to the scientific community, but many did not listen. Admitting that the cells they thought they had been working with were really HeLa cells was just too embarrassing and potentially devastating to so many careers. So people chose to just ignore the problem.
Unfortunately, HeLa cell contamination continues today. There are still cell banks selling HeLa cells under other names, often claiming that they are totally different types of cells. Scientists think they are getting a batch of oral cancer cells or liver cells, but in reality, it’s just another batch of HeLa cells.
<h6>A Lack of Informed Consent</h6>
Questions about the startling ubiquity of HeLa cells are not the only ones that have been raised since Henrietta Lacks&#8217; death. It has become clear over the decades that by not asking her permission for her cells, or informing her family about how they were being used in experiments and bought and sold literally by the millions, scientists have dishonored a woman whose death has brought life to so many others.
The emotional impact of this saga on her family has been enormous. They knew nothing of HeLa cells until they were contacted several decades after Henrietta&#8217;s death. It was by scientists who were looking for blood samples that could help them tease out more information from the HeLa cells. Imagine the shock of being told that a lost loved one was alive, in a sense, in a freezer at a university.
The family, poor and undereducated, thought they were being tested to see if they would die of cancer too. When researchers never got back to them they were left to wonder about their own fates. Today they understand more about what has happened. However, that doesn’t change the fact that they feel betrayed.
<h6>The Immortal Life of Henrietta Lacks</h6>
The questions of who owns a tissue sample or has permission to use it is hotly debated. And what are the responsibilities of researchers especially when there is money involved? (For information on how 23andMe deals with these issues, please read our <a href="https://www.23andme.com/about/privacy/" target="_blank" rel="noopener">privacy statement</a>, <a href="https://www.23andme.com/about/tos/" target="_blank" rel="noopener">terms of service</a> and <a href="https://www.23andme.com/about/consent/" target="_blank" rel="noopener">consent form.</a>) For more on this aspect of the Henrietta Lacks story, check out writer Rebecca Skloot’s <a href="http://rebeccaskloot.com/" target="_blank" rel="noopener">website. </a>There you&#8217;ll find excerpts of her book on the subject, <a href="http://rebeccaskloot.com/the-immortal-life/" target="_blank" rel="noopener">“The Immortal Life of Henrietta Lacks.”</a> (The book was published in 2010 and became a bestseller.)
The G6PD gene is on the X chromosome. That means that men have one copy and women have two. Men will therefore either be type A or B. Women on the other hand can have both types of the enzyme. The type of G6PD enzyme expressed in each of a woman&#8217;s cells depends on which of her X chromosomes is &#8220;inactivated&#8221;. 23andMe customers can check their data at rs1050829 to figure out their G6PD type.
<table border="1">
<tbody>
<tr>
<th></th>
<th>Genotype</th>
<th>G6PD Type</th>
</tr>
<tr>
<td>Men</td>
<td></td>
<td></td>
</tr>
<tr>
<td></td>
<td>C</td>
<td>A</td>
</tr>
<tr>
<td></td>
<td>T</td>
<td>B</td>
</tr>
<tr>
<td>Women</td>
<td></td>
<td></td>
</tr>
<tr>
<td></td>
<td>CC</td>
<td>A</td>
</tr>
<tr>
<td></td>
<td>TT</td>
<td>B</td>
</tr>
<tr>
<td></td>
<td>CT</td>
<td>A/B</td>
</tr>
</tbody>
</table>

The Story of Henrietta Lacks: A Lesson in Biology and Ethics

<img loading="lazy" decoding="async" class="alignright size-full wp-image-2624" title="acutelymphoblasticleukemia" src="https://blog-api.23andme.com/wp-content/uploads/2009/01/acutelymphoblasticleukemia.jpg" alt="" width="350" height="262" srcset="https://blogcms.23andme.com/wp-content/uploads/2009/01/acutelymphoblasticleukemia.jpg 350w, https://blogcms.23andme.com/wp-content/uploads/2009/01/acutelymphoblasticleukemia-300x225.jpg 300w" sizes="auto, (max-width: 350px) 100vw, 350px" />
Treatment advances have dramatically increased the cure rate for <a href="http://jama.ama-assn.org/cgi/content/full/301/4/452" target="_blank" rel="noopener noreferrer">acute lymphoblastic leukemia </a>(ALL), the most common diagnosed cancer in children, from less than 10% in the 1960’s to more than 80%.
But even in those children who are cured, the response to treatment varies from patient to patient. For some, just a couple of weeks of chemotherapy can drastically reduce the number of leukemia cells in their bone marrow, while others continue to have high levels of disease even after six weeks of intensive therapy.
Now, researchers have discovered that these differences may depend on a patient’s genetics.
Much of the previous work aimed at understanding the variability in responses to cancer treatment has focused on differences between the cancer cells themselves. But researchers from St. Jude’s Children’s Research Hospital and the Children’s Oncology Group have taken a different approach, focusing on genetic variations inherent to the cancer patients and present in all cells of their bodies.
“Although the acquired genetic characteristics of tumor cells play a critical role in drug responsiveness, our results show that inherited genetic variation of the patient also affects effectiveness of anticancer therapy….Such variation may be factored into treatment decisions in the future,” the authors write.
Their study, published online yesterday the Journal of the American Medical Association, identified more than 100 SNPs linked to the number of leukemia cells that survive after initial treatment. A significant number of these same variations were also associated with early response, relapse and drug metabolism.
Children receiving different types of chemotherapy were studied to increase the chances that the SNPs identified by the study would be associated with treatment response in general, and not just response to a specific drug. A total of 487 kids, each receiving one of three different treatment regimens for ALL, were genotyped at more than 400,000 SNPS.
In all, 102 SNPs were associated with “minimal residual disease” (MRD), a measure of the number of leukemia cells that survive after the initial phase of treatment. Some of these SNPs are very close to each other and are likely markers of the same effect, but the researchers say that they identified 72 unique regions of the genome associated with this trait.
There are differences in ALL prognosis between different racial groups. For example, African American children have been shown in some studies to have lower survival rates than white children. The researchers suggest that this could be due to differences between the two groups in the frequency of the protective versions of SNPs identified in this study. In the future, the researchers write, findings like theirs could lead to “race-neutral” treatment decisions that are based on an individual’s unique DNA make-up instead of <a href="https://blog.23andme.com/2008/08/19/the-rest-of-the-iceberg/" target="_blank" rel="noopener noreferrer">unreliable assumptions</a> based on ancestry.
Photo of bone marrow cells from an ALL patient by <a href="https://en.wikipedia.org/wiki/File:ALL-KM-2.jpg" target="_blank" rel="noopener noreferrer">Furfur</a>.

More than 100 Genetic Variations Associated with Leukemia Treatment Response

<img loading="lazy" decoding="async" class="alignright size-full wp-image-2610" title="friendwheel2" src="https://blog-api.23andme.com/wp-content/uploads/2009/01/friendwheel2.jpg" alt="" width="300" height="290" />
If Facebook is starting to take over your life, maybe your genes are partly to blame.
Researchers from UC San Diego and Harvard University have shown that certain aspects of a person’s social network — how many people consider that person a friend, the likelihood that two of a person’s friends are themselves friends, and how central a person is to their network of friends — have a genetic basis.
<h6>Genetics of Social Interactions</h6>
The results, published online yesterday in the <a href="https://www.pnas.org/content/early/2009/01/26/0806746106.abstract" target="_blank" rel="noopener">Proceedings of the National Academy of Sciences</a>, have led to the development of a new model of social interactions and could someday help scientists understand how diseases and traits like obesity, smoking and happiness spread through a population.
James Fowler, Christopher Dawes and Nicholas Christakis studied the social networks of 1,110 sets of twins from 142 separate school friendship networks and compared the similarity in friendship patterns between identical twins, who share 100% of their genes, and same-sex fraternal twins, who share about 50% of their genes.
<h6>Twins</h6>
The assumption of this type of study is that if genetic variation contributes to variation in a trait, then pairs of identical twins will be more similar to each another with respect to that trait compared to pairs of fraternal twins.
The researchers found that three measures of connectedness are heritable:
<ol>
<li>How many times a person is named as a friend</li>
<li>The likelihood of a person’s friends also being connected to each other directly</li>
<li>The tendency of a person to be along the shortest path between pairs of their friends</li>
</ol>
The number of friends people say they have, however, did not appear to have a genetic basis.
<h6>Attract and Introduce</h6>
The researchers then created a large number of simulations based on existing ideas about how human social networks form. When they observed that none of these simulated networks exhibited the same kind of heritability they saw in their real human networks, they invented a simple model they dubbed “Attract and Introduce.”
A model is simply a mathematical system that attempts to reproduce something seen in the real world based on a limited number of inputs. Every “person” in the Attract and Introduce model of social networks is given just two characteristics — a certain amount of attractiveness, which will determine how many friend nominations he or she will receive, and a certain a propensity for making introductions between new and existing friends, which will determine the number of friends who are friends with each other.
The heritability predictions produced by the Attract and Introduce model fit well with what was seen in the twin study. This suggests that their model may capture important features of how real human social networks form that existing models do not.
“There may be many reasons for genetic variation in the ability to attract or the desire to introduce friends. More friends may mean greater social support in some settings or greater conflict in others. Having denser social connections may improve group solidarity, but it might also insulate a group from beneficial influence or information from individuals outside the group,” the authors write.
Although more research will be needed to explore whether the findings in this study and the model developed apply to all people regardless of age, geography or other factors that could affect the interactions between people, this type of research has important implications. Understanding how people come together and interact could be used to predict or control the spread of communicable disease. The authors also note that their own previous research has shown that obesity, smoking behavior, happiness, and even political behavior spread in social networks.
“A full understanding of these traits may require a better understanding of the genetic basis of social network topology,” they suggest.

Miss Con-GENE-iality

<img loading="lazy" decoding="async" class="alignright size-full wp-image-2577" title="istock_000003625368xsmall" src="https://blog-api.23andme.com/wp-content/uploads/2009/01/istock_000003625368xsmall.jpg" alt="" width="300" height="199" />
Not all bacteria are bad.   Sure, there are plenty of nasty bugs that can make life pretty unpleasant; the ones that cause leprosy, anthrax, and cholera immediately come to mind.
But there are also plenty of beneficial bacteria  living inside of us that we may not even know about. Some of them help us synthesize vitamins, digest milk protein, and even stop other, more harmful microbes from infiltrating our immune system.
Many of those bacteria are so tightly connected to their human hosts that they can even be used to answer questions about our ancient ancestors. It might sound far fetched, but in a new study published in this week’s <a id="c.68" title="Science" href="http://www.sciencemag.org/" target="_blank" rel="noopener">Science</a>, an international team of scientists has managed to do this by analyzing a specific kind of bacteria hidden in the digestive system of nearly half the world’s population.   It is their hope that, by doing so, they can finally shed new light on how and when the first humans set foot on the Pacific islands.

Unearthing the origins and prehistory of the inhabitants of such islands as New Guinea, Samoa, and Polynesia has been no easy task.   Archaeological evidence has been spotty, due to the poor preservation in the tropical climate, while genetics has often been unable to distinguish between ancient migrations and more recent, historical movements.   As a result, researchers have begun turning to other disciplines to help fill in the gaps left by the more traditional fields.   In this most recent case, scientists thought outside the box, using the bacteria Helicobacter pylori — or, more accurately, differences in the genetic code of Helicobacter pylori strains — to discover when various parts of the Pacific were colonized.
Helicobacter pylori (H. pylori) is a kind of bacteria in that it is present in about 50% of the world’s population.   This makes it the most widespread bacterial infection on Earth.   It lives in our stomachs, and is sometimes associated with ulcers or an increased risk for stomach cancer.   However, more than 80% of those infected with it never know it, which may be why it is so widespread.   In fact, scientists believe that an ancient strain of H. pylori was present in the stomachs of the first humans to leave Africa more than 50,000 years ago.   Over the many thousands of years, H. pylori evolved into distinct strains found in distinct geographic regions.   For example, one strain is only found in Europe, another only in Africa, and a third only in East Asia.   So, just as genetic anthropologists use differences in our DNA to trace ancient human migrations, so too have scientists used H. pylori to reveal how humans first colonized some of the most remote parts of the world.
The current thinking about how and when the Austronesian peoples &#8211; that is, people who speak one of the many languages of island Southeast Asia and Oceania &#8211; came to colonize the Pacific Islands is, to put it mildly, unclear. While the majority of archaeologists, geneticists, and linguists all agree that the Austronesian peoples probably began their journey in present-day Taiwan, the timing and speed of their movements towards the outer rim of the Pacific Islands is a topic of great contention.   So, the authors of this most recent study hoped that an analysis of H. pylori among modern-day Austronesians might give researchers new information to go on.
The authors collected samples of the bacteria from the stomachs of more than 200 individuals living in Taiwan, New Guinea, Polynesia, and dozens of other Pacific islands.   Using techniques similar to those used in human DNA studies, the authors were able to track the different strains of H. pylori back to their common origin: Taiwan, about 5,000 years ago.
But how do these results stack up to findings by other researchers?   Interestingly, a companion piece in the same issue of <a id="u23p" title="Science" href="http://www.sciencemag.org/" target="_blank" rel="noopener">Science</a> also examined the peopling of the Pacific, this time focusing on the linguistic history of the Austronesian peoples.   That study analyzed more than 400 languages in the Austronesian linguistic family, using the similarities and differences to figure out when and where the group originated. The results of this study also support an origin of Austronesian peoples in Taiwan about 5,000 years ago.   In addition, both studies argue that people expanded in a similar direction: from Taiwan eastward towards Melanesia, Oceania, and finally Polynesia and the Hawaiian Islands.
It is not hard to believe that both the study of H. pylori and of the Austronesian languages would have yielded a similar date of origin of the Austronesian peoples, especially as both studies used the same archaeological record as a point of reference.   What is intriguing, however is that both studies &#8211; independent of each other &#8211; also point to similar paths of expansion of the Austronesian people once they left Taiwan.
The conclusions of these studies are far reaching, most especially because they illustrate how seemingly unrelated disciplines can be used to tackle a single question about the past.   Noted Cambridge archaeologist, Professor Colin Renfrew, believes these methods &#8211; combined with the more traditional archaeological or genetic methods &#8211; allow us to see how our past is still &#8216;within us&#8217; today, whether it be in our genes, in our languages, or &#8220;the bacterial flora in our guts.&#8221;

Thinking Outside the Box:  Bacterial Genetics and the Peopling of the Pacific

<img loading="lazy" decoding="async" class="alignright size-full wp-image-2571" title="doctor_reading" src="https://blog-api.23andme.com/wp-content/uploads/2009/01/doctor_reading.jpg" alt="" width="350" height="232" srcset="https://blogcms.23andme.com/wp-content/uploads/2009/01/doctor_reading.jpg 350w, https://blogcms.23andme.com/wp-content/uploads/2009/01/doctor_reading-300x199.jpg 300w" sizes="auto, (max-width: 350px) 100vw, 350px" />
It’s a situation that would leave many physicians at a loss. A 55-year-old man with a family history of dementia asks his doctor about genetic testing for Alzheimer’s disease. Is there a test? Which test should be used? Is testing even appropriate?
This week the Journal of the American Medical Association published the final installment in a three-part series of user’s guides that aims to help doctors who face these kinds of situations. Given the dizzying pace at which genetic association studies are being published and the increased availability of genetic tests, both through physicians and direct-to-consumer providers, these guides could not have come at a better time.
In the introduction to the series, the authors say that although genetic association studies may one day produce numerous benefits for both science and medicine, the most likely short-term use of this type of information for clinicians is in identifying the most at-risk people in a population and providing patients with information on the likely courses their diseases will take.
Although the user’s guides are intended for physicians, they are written in such a clear and concise manner that anyone interested in understanding more about genetics and how it applies to their health will find them helpful.
(Unfortunately these guides are not freely available. They may be available at a local city, county or university library. They are also available for download for $15 per article.)
Summary of the three user’s guides:
<h6><a href="http://jama.ama-assn.org/cgi/content/abstract/301/1/74" target="_blank" rel="noopener">A. Background Concepts</a></h6>
The first article summarizes the key genetic concepts that clinicians must be familiar with to understand genetic association studies. There is a glossary of commonly used terms, a review of the components and structure of DNA, an explanation of human variation and a summary of the different forms that genetic association studies can take.
<h6><a href="http://jama.ama-assn.org/cgi/content/abstract/301/2/191" target="_blank" rel="noopener">B. Are the Results of the Study Valid?</a></h6>
The second article takes the reader through the major issues that need to be addressed in judging whether a genetic association study is valid, presenting a series of questions physicians should ask themselves while reading an association study. Topics addressed include determining whether the participants used in a study were chosen correctly, how to tell if the technology being used to genotype study participants worked correctly, several statistical considerations that need to be addressed (including <a href="https://blog.23andme.com/2009/01/14/cereal-killer-the-tragic-tale-of-a-fatal-statistical-flaw/" target="_blank" rel="noopener">multiple testing</a>) and whether the results have been replicated and are consistent with those of other studies.
<h6><a href="http://jama.ama-assn.org/cgi/content/abstract/301/3/304" target="_blank" rel="noopener">C. What are the Results and Will They Help Me in Caring for My Patients?</a></h6>
The concluding article of the series offers guidance on evaluating the magnitude and precision of a study’s findings and determining what to do with these results, based on both the study and the patient&#8217;s family history and personal characteristics.

JAMA Publishes User’s Guides to Help Physicians Understand Genetic Association Studies

<img loading="lazy" decoding="async" class="alignright size-full wp-image-2564" title="cancer_microscope" src="https://blog-api.23andme.com/wp-content/uploads/2009/01/cancer_microscope.jpg" alt="" width="350" height="222" srcset="https://blogcms.23andme.com/wp-content/uploads/2009/01/cancer_microscope.jpg 350w, https://blogcms.23andme.com/wp-content/uploads/2009/01/cancer_microscope-300x190.jpg 300w" sizes="auto, (max-width: 350px) 100vw, 350px" />
Each type of cancer has its own idiosyncrasies, but when it comes down to it, they all have one thing in common: failure to control cellular growth. So it’s somewhat surprising that when genome-wide association studies have looked for single common variations associated with the risks for multiple types of cancer, they have for the most part identified only SNPs that are peculiar to just one form of the disease.
A new study published online Sunday in <a href="https://dx.doi.org/10.1038/ng.296" target="_blank" rel="noopener">Nature Genetics</a> may signal a change in this trend. A team of researchers led by Thorunn Rafnar and Patrick Sulem of deCODE Genetics in Iceland describes how a genetic variation they originally found to be associated with the risk for developing basal cell carcinoma (BCC), a type of skin cancer, is also linked to increased odds for four other cancers.
In a study of more than 33,800 cancer patients and 45,800 controls, the scientists found that a variant associated with increased odds of lung, bladder, prostate and cervical cancer, in addition to the previously found association with BCC. This variation decreases the odds of cutaneous melanoma, another type of skin cancer.
The variant was also marginally, although not significantly, associated with increased odds of endometrial cancer and decreased odds of colorectal cancer.
There was no association of the SNP with cancer of the breast, kidney, stomach, thyroid, ovary or pancreas, nor with lymphoma, multiple myeloma or squamous cell carcinoma (a third type of skin cancer). The authors say that further investigation in even larger samples will be needed to determine if there truly is no association, or if they just haven’t picked it up yet.
An association was also found between a nearby variant and four of the five cancers that were associated with it.
Both SNPs are near a gene involved in maintaining the protective stretches of DNA attached to the ends of chromosomes called telomeres. The authors suggest that these SNPs, or other nearby variations, may lead to shortened telomeres, which are associated with several types of cancer.
Telomere length is determined in part by genetics, but environmental factors such as smoking and radiation can also shorten them. The authors note “four of the five cancers associated with the risk variants are cancer types that have strong environmental contributions to risk — smoking and occupational exposures for lung and bladder cancer, UV irradiation for BCC and infection with human papillomavirus for cervical cancer.” More research could help explain the exact relationship between the genetic variations found in this study and the environmental causes of these cancers.

One Variation, Many Cancers

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It sounds like something from a nightmare: decades after eating a tainted hamburger you develop an incurable, fatal disease that literally eats holes in your brain.
Unfortunately, for some people, this is a nightmare that is all too real. In the 1990s a small number of people in the UK developed a variant form of a disease called Creutzfeldt-Jakob disease (vCJD) after eating meat from cattle infected with bovine spongiform encephalopathy (BSE), or “mad cow disease”.
Every one of the documented vCJD cases in the UK has been in a person with two copies of the “M” variant of a gene called PRNP. People with just one or with no copies of this variant — MV and VV individuals, respectively &#8212; have been thought to be protected from developing vCJD. But the British media (<a href="http://news.bbc.co.uk/1/hi/health/7788627.stm" target="_blank" rel="noopener noreferrer">here</a>, <a href="http://news.sky.com/skynews/Home/Possible-New-Version-Of-Human-Mad-Cow-Disease-Experts-Warn-Of-vCJD-Second-Wave-Of-Deaths/Article/200812315185658?f=rss" target="_blank" rel="noopener noreferrer">here</a> and <a href="http://www.independent.co.uk/life-style/health-and-wellbeing/health-news/fears-raised-for-new-wave-of-vcjd-cases-1202641.html" target="_blank" rel="noopener noreferrer">here</a> for examples) recently reported a case of apparent vCJD in someone with the MV genotype, raising concerns that more people in the UK could be at risk.
But in an email to the Blog, the UK’s Spongiform Encephalopathy Advisory Committee chair Christopher Higgins wrote, “There are no confirmed vCJD clinical cases in MV or VV. 100% of clinical cases are in MM. The latest reports concern someone who is definitely MV but a clinical diagnosis of vCJD has not yet been confirmed — and may not be for some time.”
Higgins said that if MV and VV individuals were just as susceptible to infection with vCJD as MM individuals, the theoretical maximum number of additional cases the UK might see would be about 300.
But, he stressed, this is a big if.
“This is a maximum and I personally suspect the numbers will be very much less and could even be zero.”
Higgins said that mouse studies and research involving <a href="https://en.wikipedia.org/wiki/Kuru_(disease)" target="_blank" rel="noopener noreferrer">kuru</a>, another type of spongiform encephalopathy, indicate that people with the MV and VV genotypes are less easily infected than MM individuals. Furthermore, these same studies have shown that if MV and VV individuals are infected, the incubation period between infection and development of the disease would be expected to be greatly extended.
“Thus many may die of other causes or simply ‘old age’ before clinical vCJD has a chance to emerge,” he said.
Higgins noted that in the UK, BSE has been effectively eradicated from the beef industry and precautions have been put in place to minimize the chance of person-to-person transmission of vCJD, meaning that anyone who was going to be infected would have been infected during the BSE crisis of the 1980s to mid-1990s.
“Younger people of any genotype should have little to worry about,” he said.
Finally, Higgins pointed out that the risk of vCJD should be kept in perspective.
“Compared with the 3000 people per year who die in road accidents, the total number of people who will ever die of BSE/vCJD is likely to be much less,” Higgins said. He estimates that no more than about 200 cases of vCJD in MM individuals will ever be seen in the UK, and said that around 160-170 cases of vCJD have already been diagnosed and the numbers diagnosed annually are now very low, indicating that the epidemic could be past its peak.
“There are far more important things in life to worry about.”

No Good Evidence That Potential Pool of Mad Cow Disease Victims Is Expanding

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The cells in our bodies are subject to a constant onslaught of potentially damaging chemicals. Some of these come from the environment — the toxins in cigarette smoke, for an example — while others are natural byproducts of cellular life. Regardless of their origin, these chemicals have the potential to cause serious DNA damage that can eventually result in cancer.
Cells have evolved numerous mechanisms for defusing the danger posed by these chemicals. In the event that these efforts fail and DNA damage does occur, cells also have their own DNA repair systems. Not surprisingly, mutations in the genes that encode these DNA-fixers can leave cells vulnerable and increase the chances that a cancer will develop. Bloom’s syndrome, Fanconi anemia and hereditary breast cancers caused by BRCA mutations are all examples of cancer syndromes caused by relatively rare functional mutations in DNA repair genes.
Research from the University of Texas M.D. Anderson Cancer Center in Houston published online today in <a href="https://dx.doi.org/10.1158/1078-0432.ccr-08-1607" target="_blank" rel="noopener noreferrer">Clinical Cancer Research</a> shows that common variations, not just rare mutations, in DNA repair genes can increase the risk for pancreatic cancer.
Pancreatic cancer is the fourth leading cause of cancer death for both men and women in the United States. Environmental factors such as smoking, obesity, diabetes, chronic pancreatitis and dietary factors are known to play a part in determining the risk of pancreatic cancer, but about 10% of patients have a family history of the disease, suggesting that there are also genetic risk factors.
Donghui Lie and colleagues examined variations in several DNA repair genes among 734 non-Hispanic white pancreatic cancer patients and 780 people without the disease. They found that having two copies of the A version of rs1801516 in the ATM gene increased the odds of pancreatic cancer 2.76 times compared to two Gs. Having just one copy of the A version did not significantly increase risk.
SNPs in the ATM gene have also been associated with an increased risk of developing breast cancer. The protein encoded by ATM is known to be crucial for the cellular response to DNA damage.
The researchers also found a significant association between having two copies of the A version of rs2074522 in the LIG3 gene (also involved in DNA repair) and risk for pancreatic cancer. 23andMe does not currently provide data on this SNP.
“Pancreatic cancer is a highly fatal disease because most of the cases are diagnosed at late stage and the tumors are resistant to most therapies. Early detection for pancreatic cancer is crucial to reduce the mortality,” the authors write.
“However, there is no screening method available to identify the high-risk individuals among those at risk,” they write &#8212; referring to people such as smokers, people with diabetes, and those with a family history of pancreatic cancer.
The authors suggest that in addition to aiding in the development of screening tests for pancreatic cancer, finding and understanding variants such as those identified in their study will help aid in developing new treatments.

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