<img loading="lazy" decoding="async" class="alignright size-full wp-image-6209" title="6Denisova_cave" src="https://blog-api.23andme.com/wp-content/uploads/2010/03/6Denisova_cave.jpg" alt="" width="346" height="517" />Denisova cave from the outside. / Bence Viola. 
DNA isolated from a tiny bone fragment from the finger of a being that walked the earth between 30,000 and 50,000 years ago has possibly added a new branch to the human family tree.
<h6>denisovan</h6>
The piece of bone was found in the Denisova Cave in the Altai Mountains, Russia.   Thanks to the preserving effects of the area&#8217;s relatively chilly temperatures, researchers from the Max Planck Institute for Evolutionary Anthropology were able to recover mitochondrial DNA (mtDNA) suitable for sequencing.
Their results, published online today in the journal <a href="https://dx.doi.org/10.1038/nature08976" target="_blank" rel="noopener">Nature</a>, show that compared to present-day humans, mtDNA from the so-called &#8220;Denisova <a href="http://archaeology.about.com/od/hterms/g/hominin.htm" target="_blank" rel="noopener">hominin</a>&#8221; contains twice as many differences as do mtDNAs from Neanderthals.
<h6>Another Human Cousin</h6>
From this the researchers conclude that the Denisova hominin was a member of a previously unknown species of human ancestor.   Further analysis allowed them to estimate that the most recent common maternal ancestor shared by all three species lived about one million years ago.
&#8220;Their discovery is remarkable not just for the insight it gives into the human past.   For the first time a hominin has been described, not from the morphology of its fossilized bones, but from the sequence of its DNA,&#8221; wrote Terence A. Brow, in a News &amp; Views article that accompanied the Nature study.
There is evidence that both Neanderthals and anatomically modern humans were in the area of the Denisova cave at around the same time as the individual whose mtDNA was sequenced in the current study. This suggests that each wave of hominins that moved out of Africa and into Eurasia did not replace the last.   Instead, multiple lineages coexisted for long periods of time.
More work will be needed to definitively determine the relationship of the Denisova hominin to Neanderthals and modern humans.   Ongoing research is attempting to isolate nuclear DNA for further comparisons and to look for evidence of interbreeding.
<h6>Update 3/29/10</h6>
There&#8217;s quite a bit of discussion about whether or not the Denisova hominin really is a distinct species. A good place to learn more about the debate is Carl Zimmer&#8217;s blog The Loom.   <a href="http://theatavism.blogspot.com/2010/03/does-forty-thousand-year-old-finger.html" target="_blank" rel="noopener">The Atavism</a> also has a post about this topic.
<ul>
<li>Read more about this story at ScienceNews.</li>
<li>More from the Blog on ancient DNA:
<ul>
<li><a href="../2010/02/10/researchers-use-snp-analysis-to-paint-picture-of-an-ancient-human/" target="_blank" rel="bookmark noopener">Researchers Use SNP Analysis to Paint Picture of an Ancient Human</a></li>
<li><a href="../2009/02/12/researchers-announce-draft-version-of-complete-neanderthal-genome/" target="_blank" rel="bookmark noopener">Researchers Announce Draft Version of Complete Neanderthal Genome</a></li>
<li><a href="../2009/07/22/novel-techniques-suggest-neanderthal-populations-dwindled-in-the-face-of-expanding-humans/" target="_blank" rel="bookmark noopener">Novel Techniques Suggest Neanderthal Populations Dwindled in the Face of Expanding Humans</a></li>
</ul>
</li>
</ul>

23andMe Blog

23andMe Blog Team

Ancient DNA of An Extinct Human Ancestor

<img loading="lazy" decoding="async" class="alignright size-full wp-image-6195" title="iStock_000001799352XSmall" src="https://blog-api.23andme.com/wp-content/uploads/2010/03/iStock_000001799352XSmall.jpg" alt="" width="338" height="224" srcset="https://blogcms.23andme.com/wp-content/uploads/2010/03/iStock_000001799352XSmall.jpg 425w, https://blogcms.23andme.com/wp-content/uploads/2010/03/iStock_000001799352XSmall-300x199.jpg 300w" sizes="auto, (max-width: 338px) 100vw, 338px" />
From rich brown to almost translucent white, human skin colors span a remarkable spectrum.
The evolutionary story of how we came to be such a varied species skin color-wise began around 40,000 years ago when the human groups that had left Africa and spread out along the southern coast of Asia began to move north.
When people lived near the equator, greater concentrations of the pigment <a href="https://en.wikipedia.org/wiki/Melanin" target="_blank" rel="noopener">melanin</a> in their skin, hair and eyes acted as a natural sunblock to protect them from high levels of cancer-causing ultraviolet radiation. But melanin also reduces the body&#8217;s production of vitamin D, which is stimulated by ultraviolet radiation. At higher latitudes, where vitamin D deficiency is more of a survival issue than skin cancer, genetic changes that reduced melanin production were favored by natural selection.
Although the overall theory of how non-African populations came to lose some of their color is pretty well accepted, there is still a lot to learn about the details.   
Much of the research has focused on European populations.   Now a new study, published recently in the journal <a href="https://dx.doi.org/10.1371/journal.pgen.1000867" target="_blank" rel="noopener">PLoS Genetics</a>, has identified a DNA variant involved in pigmentation that is specific to East Asian populations.
Scientists led by Esteban Parra of the University of Toronto focused their search for determinants of different shades of East Asian skin color on 10 SNPs in five genes already known to be involved in pigmentation.   They analyzed the DNA of 122 people with East Asian ancestry living in Canada, and combined the genetic information with quantitative measurements of skin color.
The scientists found a variant associated with a 1.3 melanin unit reduction in skin pigmentation.
Although this is a small difference (variations associated with pigmentation identified in other populations have had effects of around 3 melanin units per copy), the researchers calculate that this SNP accounts for 9% of the variation in skin color seen in the study population.
The researchers replicated their finding of an association of with skin pigmentation in a group of 207 Han Chinese people living in China, although the effect of the variation, and the percent of the variability in skin color explained, was somewhat smaller.
Genetic evidence has previously suggested that the transition from melanin-rich to melanin-poor skin took place independently in the groups that would eventually become the populations we now call European and East Asian.   The current study further supports this idea of &#8220;convergent evolution.&#8221;   is in OCA2, a gene that has also been associated with pigmentation in European populations.
The variations associated with lighter skin in Europeans are not found in East Asians, however, and the C version of has not been found in Europeans.
Further research in diverse groups will be needed to understand exactly how human pigmentation has evolved around the world, and when in our history these changes took place.

Genetics of Skin Color Differences in East Asians

<img loading="lazy" decoding="async" class="alignright size-full wp-image-1496" title="ribbon" src="https://blog-api.23andme.com/wp-content/uploads/2008/10/ribbon.jpg" alt="" width="350" height="260" srcset="https://blogcms.23andme.com/wp-content/uploads/2008/10/ribbon.jpg 350w, https://blogcms.23andme.com/wp-content/uploads/2008/10/ribbon-300x223.jpg 300w" sizes="auto, (max-width: 350px) 100vw, 350px" />
A paper published in the New England Journal of Medicine (NEJM) this week, entitled &#8220;<a href="http://content.nejm.org/cgi/content/short/362/11/986" target="_blank" rel="noopener">Performance of Common Genetic Variants in Breast-Cancer Risk Models</a>,&#8221; has led several media outlets to declare that common genetic variants have nothing to add when it comes to predicting breast cancer risk.   Here we&#8217;ll explain how the results of this study have been misinterpreted.
Researchers from the National Cancer Institute and other institutions looked at data from 5,590 women with breast cancer and 5,998 women without the disease.   These women, all between 50 and 79 years old, had participated in one of five studies, four in the United States and one in Poland.   Since it&#8217;s known already which women have or have had breast cancer, and which have not, the researchers were able to use their data, both genetic and non-genetic, to test the predictive power of different types of risk calculations.
The study tested five different models.   The &#8220;demographic model&#8221; considered only age, year of entry into the study and which study the woman was originally part of.   The &#8220;nongenetic model&#8221; added in several variables that are part of the so-called &#8220;Gail model,&#8221; which is the standard model used in clinical practice today to counsel women about their risk.   These variables were the number of first-degree relatives with a diagnosis of breast cancer, age at menarche, age at first live birth, and number of previous breast biopsies.   Two models used the demographic information plus genetic information for 10 SNPs (they differed in details of how the genetic risk score was calculated).   Finally, the &#8220;inclusive model&#8221; combined demographics, the Gail model and the genetic information.
The genetic models and the nongenetic model performed about the same, with genetics doing just a little bit better.   Perhaps not surprisingly, the best model was the one that used the most information.   With the inclusive model, which is based on genetic and non-genetic information, there was a net 12% improvement in risk classification over the nongenetic model for women with breast cancer.
So, SNPs did add something.   The improvement in prediction seen when SNPs are added to the nongenetic model is about the same as the improvement seen when the Gail model information is added to the simplistic demographic model.   Discounting the benefit of adding SNP information to the Gail model implicitly discounts the utility of the Gail model itself.   Peter Devilee and Matti A. Rookus made this very point in a <a href="http://content.nejm.org/cgi/content/short/362/11/1043" target="_blank" rel="noopener">NEJM editorial</a> that accompanied the study.
It&#8217;s also important to remember that the study of common variations and their effect on common diseases like breast cancer is a relatively young science.   Many more variants are bound to be discovered, and these will only help further refine risk predictions.
It&#8217;s true that there is a cost associated with collecting a person&#8217;s genetic information, while collecting the information needed for the Gail model is essentially free.   (In fact, a risk calculator based on the Gail model is available at the <a href="http://www.cancer.gov/bcrisktool/" target="_blank" rel="noopener">National Cancer Institute website</a>.) But for those people who do have their genetic information in hand, the current study shows that it can improve the estimation of their risk for breast cancer.   It should be remembered, too, that not everyone is fortunate enough to have access to their family medical history. Adoptees, for example, cannot get an accurate picture of their breast cancer risk from the Gail model.   For such women, the ability to use their own genetics to help assess their risk for breast cancer is an option that should not be dismissed.
Ultimately, it&#8217;s not about genetics vs. non-genetics &#8212; it&#8217;s about getting accurate estimates of risk to help doctors catch cancers early on, when they&#8217;re easiest to beat. Researchers should welcome any tool that can help them move closer to keeping more women healthy.   Giving up on genetics this early on in the game would be a real disservice.
Note: A similar study can be found in <a href="http://precedings.nature.com/documents/4295/version/1" target="_blank" rel="noopener">Nature Precedings</a>.   The results are consistent with the NEJM study regarding the improvement in risk prediction when SNP information is added to the Gail model.   This work also shows that the improvement is larger for women at intermediate risk who are more likely to be reclassified.   Senior author David Hinds was at Perlegen Sciences when this paper was written and is currently an employee of 23andMe, Inc.

Confusion Over Utility of Common Genetic Variations in Breast Cancer Risk Prediction

<img loading="lazy" decoding="async" class="alignright size-full wp-image-6151" title="allergy" src="https://blog-api.23andme.com/wp-content/uploads/2010/03/allergy.jpg" alt="" width="285" height="253" />
Spring is about to, well, spring.   And for many of us, that means breaking out the Benadryl ® and the tissues as pollen fills the air and our allergies kick in.
Allergies are part of the daily lives for <a href="http://www.aafa.org/display.cfm?id=9&amp;sub=30" target="_blank" rel="noopener noreferrer">one out of four Americans</a>, making allergies more common than heart disease, cancer and diabetes combined.   For many people, allergies involve only symptoms that are a nuisance, like sneezing or itchy eyes.  But for some, contact with certain substances can lead to life-threatening anaphylactic shock.   To study this mysterious and growing problem, we&#8217;ve released our first allergy survey.
Allergies occur when your body reacts to a normally harmless substance, called an allergen, like it&#8217;s a dangerous invader.   Your immune system produces IgE antibodies that recognize the allergen and trigger the release of histamines.   While histamines normally help protect your body against infections, they can cause allergy symptoms when released inappropriately.   This is why many allergy medications are called &#8220;anti-histamines&#8221;.
The biological process of how symptoms occur after the release of histamines is relatively well-understood, but the question of why the immune systems of people with allergies react to otherwise inoffensive substances like pollen or peanuts remains.   There is a growing body of evidence that supports the &#8220;hygiene hypothesis.&#8221;   This <a href="https://www.ncbi.nlm.nih.gov/pubmed/18650915" target="_blank" rel="noopener noreferrer">theory</a> says that our immune systems need early exposure to parasites like roundworms and tapeworms to mature properly.   Without such exposure the risk of developing allergies is increased.   This fits with the observation that allergies are more common and generally on the rise in industrialized countries where parasite infections are far less common than in the developing world.
It is also clear, however, that genetics play a large role in whether you develop allergies.   Having a family history of allergy puts you at much higher risk for also having an allergy, although it may not be the same type. For example, a family history of asthma, which is a type of allergic disease in most cases, puts you at <a href="https://www.cdc.gov/healthyyouth/foodallergies/" target="_blank" rel="noopener noreferrer">higher risk for a food allergy</a>. While a few <a href="https://www.ncbi.nlm.nih.gov/pubmed/18301422" target="_blank" rel="noopener noreferrer">genes</a> have been shown to be associated with allergy, the genetic picture is far from complete.   If by learning more about the genetics of allergy we could help predict which children may be more likely to develop a dangerous food allergy for example, precautionary measures could be taken.   In addition, we may discover better ways to treat different allergies.
At best, allergies are annoying.   At worst, they&#8217;re deadly.   You can help us take the first steps to understanding the genetics of allergy by completing our new allergy survey.   In the meantime, I&#8217;ll be investing in Kleenex!

23andMe Allergy Survey: Nothing to Sneeze At

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Today the National Institutes of Health (NIH) announced its plans to create a public database in which genetic test providers will voluntarily deposit information about their services that can then be searched by researchers, consumers, health care providers, and others. The aim of this Genetic Testing Registry, which is expected to be launched in early 2011, is to enhance access to information about the availability, validity, and usefulness of genetic tests.
&#8220;The need for this database reflects how far we have come in the last 10 years,&#8221; said NIH Director Francis S. Collins, M.D., Ph.D., in a <a href="http://www.nih.gov/news/health/mar2010/od-18.htm" target="_blank" rel="noopener">press release</a>. &#8220;The registry will help consumers and health care providers determine the best options for genetic testing, which is becoming more and more common and accessible.&#8221;
&#8220;We welcome the news of the Genetic Testing Registry,&#8221; said 23andMe co-founder Anne Wojcicki in response to the announcement. &nbsp; &#8220;23andMe has always been committed to providing individuals with the information they need to make the most of their own genetic information. &nbsp; We look forward to working with the NIH on this project.&#8221;
More information about the Genetic Testing Registry is available from the National Center for Biotechnology Information<a href="https://www.ncbi.nlm.nih.gov/gtr/" target="_blank" rel="noopener"> here</a>. &nbsp; Comments and questions can be submitted from this page. &nbsp; There is also a list of background reading materials.
Francis Collins has done several interviews in the past few weeks where he has discussed the role of genetics in health care, now and in the future. A quick video interview with the Washington Post can be seen here. &nbsp; An hour long interview he did on the Diane Rehm show is available <a href="http://thedianerehmshow.org/shows/2010-03-04/national-institutes-health-director-dr-francis-collins" target="_blank" rel="noopener">here</a>.

NIH to Create Public Database of Genetic Tests

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Today at the American College of Cardiology conference in Atlanta, researchers from the Mayo Clinic and Medco Health Solutions, Inc., presented results showing that using genetic testing to guide dosing of the commonly used blood thinner warfarin reduces hospitalizations.
Overall there were 31% fewer hospitalizations within six months of beginning warfarin therapy in those who received genetic testing compared to those who didn&#8217;t. A 28% drop in hospitalizations due specifically to bleeding or blood clots was seen.
&#8220;Warfarin represents an excellent example of how to take the modern science of genetic testing and apply it to making an older drug more effective and safer to use,&#8221; said Dr. Robert S. Epstein, lead author of the study and Medco&#8217;s chief medical officer and president of the Medco Research Institute, in a press release.  &#8220;These results show that we can greatly reduce hospitalizations, and their significant costs, by making genetic testing routine early in a patient&#8217;s therapy with warfarin.&#8221;
Although a variety of factors influence a patient&#8217;s ideal dose of warfarin, variations in the CYP2C9 and VKORC1 genes play an important part.   The FDA has mandated that information about these variants be included in the labeling information of the medication since 2007.   In February of this year they <a href="https://blog.23andme.com/2010/02/04/fda-updates-label-on-commonly-used-blood-thinner-to-include-dosing-recommendations-based-on-genetics/" target="_blank" rel="noopener noreferrer">updated the drug&#8217;s label</a> to include specific dosage recommendations.
Genetic testing before administration of warfarin, however, is not mandatory.   There has been significant disagreement over whether or not health outcomes are actually impacted when genetic information is available to physicians.   In fact, the Centers for Medicare and Medicaid Services, the federal agency that makes decisions about what Medicare, Medicaid and the Children’s Health Insurance Program will cover, decided last year that there was not sufficient evidence to justify covering genetic testing before warfarin administration for Medicare beneficiaries.  It will be interesting to see if the new study, which will soon be published in the Journal of the American College of Cardiology, will change this stance.
<a href="http://www.theheart.org/article/1058617.do" target="_blank" rel="noopener noreferrer">theheart.org</a> has more on this story, including comments from researchers critical of the research.   The PowerPoint slides used in the researchers&#8217; presentation are also available for download. (Free registration required)

Genetic Tests Can Reduce Risks From Blood Thinner Warfarin

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The U.S. Food and Drug Administration (FDA) has <a href="https://www.fda.gov/Drugs/DrugSafety/PostmarketDrugSafetyInformationforPatientsandProviders/ucm203888.htm" target="_blank" rel="noopener noreferrer">updated the label information</a> for the commonly used anti-clotting medication Plavix ® (clopidogrel) to stress to physicians that patients carrying certain genetic variations may not receive the full benefit from the drug.
Plavix reduces the chance a harmful clot will develop by preventing blood cells called platelets from sticking together. Usually prescribed in combination with aspirin, Plavix has been shown to help reduce the risk of subsequent heart attacks or strokes in people who have already suffered from a cardiovascular event. Plavix also reduces the risk of heart attack and stroke in people diagnosed with peripheral artery disease.   The drug is also is used to lower the risk of blood clots in people with unstable angina (chest pain) caused by partially blocked arteries and in those who have had a stent implanted to help keep their arteries open.
Once inside the body, Plavix is absorbed in the intestines and then converted into its active form by enzymes in the liver. But some people have genetic variations that reduce the activity of one of the most critical enzymes – CYP2C19. This, in turn, reduces the amount of active drug in the bloodstream and its effectiveness in preventing clots.
The FDA first added information about poor metabolizers of Plavix to the drug label in May 2009. Additional data has prompted them to add the boxed warning to further caution physicians that some of their patients may be at risk, inform them that testing for CYP2C19 variations is available (although no test is FDA-approved specifically for determining Plavix efficacy), and recommend that other medications or increased dosages of Plavix be used in patients identified as poor metabolizers.
“We want to highlight this warning to make sure health care professionals use the best information possible to treat their patients,” said Mary Ross Southworth, Pharm.D., a clinical analyst in the Division of Cardiovascular and Renal Products in the FDA’s Center for Drug Evaluation and Research, in a press release.
A recently approved drug, Effient ® (prasugrel), may be an alternative for some patients identified as poor metabolizers. Like Plavix, Effient prevents platelets from forming blood clots. The advantage is that the conversion of Effient to its active form can take place in the presence of the genetic variations that affect Plavix. Studies have shown that Effient is effective at preventing heart attacks, strokes and stent-blocking clots.   The risk of dangerous bleeding, however, is higher with this drug.
23andMe Health Edition and Complete Edition customers can view their data for genetic variations in CYP2C19 in the Clopidogrel (Plavix) Efficacy Drug Response Report.
A downloadable PDF version of the Clopidogrel (Plavix) Efficacy report is available to help customers share their results with their doctors.
Only a physician can determine whether Plavix is the right medication for a particular patient and at what dosage it should be given.   The information contained in 23andMe Drug Response reports should not be used to independently establish a drug regimen or abolish or adjust an existing course of treatment.   If you are concerned about Plavix, talk to a health professional.
<ul>
<li>Read more about the Plavix label update<a href="http://www.genomeweb.com/blog/fdas-new-plavix-black-box-warning-could-trigger-surge-cyp2c9-testing" target="_blank" rel="noopener noreferrer"> here </a>and here.</li>
<li>Just last month the FDA updated the label on another anti-clotting medication, warfarin, to include more information on the effects of genetic variations.   Read more<a href="https://blog.23andme.com/articles/fda-updates-label-on-commonly-used-blood-thinner-to-include-dosing-recommendations-based-on-genetics" target="_blank" rel="noopener noreferrer"> here </a>in the Blog.</li>
</ul>

FDA Adds Boxed Warning to Plavix Label to Highlight Reduced Effectiveness of the Drug In Poor Metabolizers

<img loading="lazy" decoding="async" class="alignright size-full wp-image-3242" title="colon" src="https://blog-api.23andme.com/wp-content/uploads/2009/04/colon.jpg" alt="" width="360" height="240" srcset="https://blogcms.23andme.com/wp-content/uploads/2009/04/colon.jpg 360w, https://blogcms.23andme.com/wp-content/uploads/2009/04/colon-300x200.jpg 300w" sizes="auto, (max-width: 360px) 100vw, 360px" />

<a href="http://www.nlm.nih.gov/medlineplus/colorectalcancer.html" target="_blank" rel="noopener">Colorectal cancer</a> is the third most common cancer (excluding skin cancers) and the second leading cause of cancer-related deaths in the United States.
Each year about 150,000 people are diagnosed with the disease.
Risk factors for colorectal cancer include age (most cases occur in people over 50), ethnicity (African Americans and Ashkenazi Jews have particularly high rates of the disease), a personal history of colon polyps or colorectal cancer, and the presence of inflammatory bowel disease (Crohn&#8217;s disease or ulcerative colitis).  
Obesity, physical inactivity, smoking and heavy drinking have also all been associated with increased risk for colorectal cancer.
Genetics contribute to a person&#8217;s colorectal cancer risk, although non-genetic factors seem to play a larger role.  
About 5% of people with colorectal cancer, however, develop the disease as a result of either <a href="http://www.clevelandclinic.org/registries/inherited/fap.htm" target="_blank" rel="noopener">familial adenomatous polyposis</a> (FAP) or <a href="http://www.mayoclinic.com/health/lynch-syndrome/DS00669" target="_blank" rel="noopener">Lynch syndrome</a>, two cancer syndromes caused by serious genetic mutations.
Anyone with a family history of colorectal cancer should talk to their health care professional about what screening procedures, and possibly what genetic tests, are right for them.
Research to find common genetic variants associated with colorectal cancer risk has yielded several good associations, but together they explain only a small part of the genetic contribution to the disease.
There are probably many more variants with small effects left to be found, as well as rare variants with larger effects.   
Learn More About Your Risk
Several online tools are available to help you get a better idea of your risk for colorectal cancer.

<ul>
<li>National Cancer Institute </li>
<li><a href="http://www.siteman.wustl.edu/crc.aspx?id=459" target="_blank" rel="noopener">Washington University School of Medicine Siteman Cancer Center </a></li>
<li>My Family Health Portrait &#8211; a free online tool provided by the Surgeon General that can help you assemble your family&#8217;s health history</li>
</ul>
Get Involved
You can contact the following organizations to learn more about colorectal cancer and find out how to get involved in Colorectal Cancer Awareness Month.
<ul>
<li><a href="http://www.ccalliance.org/" target="_blank" rel="noopener">Colon Cancer Alliance</a></li>
<li><a href="http://www.cancer.org/docroot/home/index.asp" target="_blank" rel="noopener">American Cancer Society</a></li>
</ul>
And for those who want an up-close lesson about colorectal cancer, click <a href="http://www.preventcancer.org/education2c.aspx?id=3794" target="_blank" rel="noopener">here</a> to see if the Prevent Cancer Super Colon is coming to a town near you.

March is Colorectal Cancer Awareness Month

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Researchers have identified several genetic variations associated with the timing of a baby&#8217;s first tooth and the number of teeth at age one. The results, published recently in the journal <a href="http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1000856" target="_blank" rel="noopener">PLoS Genetics</a>, could be important for understanding more about human health than just this rite of passage all babies must go through.
Nascent teeth form in the womb, but for most babies the first one doesn&#8217;t poke through the gums until sometime<a href="http://www.babycenter.com/0_developmental-milestones-teething_6574.bc" target="_blank" rel="noopener"> between four and seven months</a> of age. Some little ones, however, begin teething as early as three months, while others may take a year or more to sprout their first pearly whites. Although the genetic bases for many syndromes involving serious problems with tooth formation have been discovered, until now not much work has been done to understand how our DNA impacts the normal variation in teething seen in the population.
British and Finnish researchers analyzed the DNA of about 6,000 people (approximately 1,500 from the U.K. and 4,500 from Finland) who had been followed by epidemiologists since early in their mothers&#8217; pregnancies. Genetic variants in 10 different regions of the genome had at least a suggestive link to age at first tooth eruption and/or number of teeth at one year. Those SNPs with statistically significant associations with at least one of the traits are shown in the table below.
<img loading="lazy" decoding="async" class="alignright size-full wp-image-6079" title="plos_figure" src="https://blog-api.23andme.com/wp-content/uploads/2010/03/plos_figure.jpg" alt="" width="333" height="238" srcset="https://blogcms.23andme.com/wp-content/uploads/2010/03/plos_figure.jpg 450w, https://blogcms.23andme.com/wp-content/uploads/2010/03/plos_figure-300x215.jpg 300w" sizes="auto, (max-width: 333px) 100vw, 333px" />Subjects are classified by the number of delayed tooth eruption alleles. SNPs are chosen so that they had the strongest signal for number of teeth at each locus. Mean time of first tooth eruption is plotted in red and number of teeth by the age of one year in black. The bars represent the number of individuals for each count of ‘delayed tooth eruption’ alleles. The line through points is a linear regression fit. doi:10.1371/journal.pgen.1000856.g002 

Much as has been the case for genetic associations with <a href="https://blog.23andme.com/2008/04/07/snpwatch-large-studies-find-snps-with-small-effects-on-height/" target="_blank" rel="noopener">height</a>, another highly heritable and complex human trait, the variations the researchers linked with teething characteristics explain only a tiny fraction–about 3-4%–of the total variance seen in the population. More studies, with larger samples, will be needed in order to identify more SNPs, including those with smaller effect sizes and rare variants.
Based on the significant SNPs found in the study, the authors defined a summary statistic called the &#8220;delayed tooth eruption measure,&#8221; which is calculated by adding up how many copies of the &#8220;delayed&#8221; version of each SNP a person carries. For women the total possible is 10 (two copies of each of five SNPs). Because one of the SNPs is on the X chromosome, for men the total possible is nine.
Based on the Finnish sample, the researchers calculated that individuals with a delayed tooth eruption measure of eight or more have an average of 1.5 fewer teeth at 12 months of age, and later tooth eruption by 1.1 months, compared to individuals with a score of three or less.
The researchers also evaluated whether or not any of the SNPs found in their study of infant teething were associated with the need for orthodontic treatment by age 31 in their Finnish sample. The only significant finding was a SNP that showed only suggestive evidence for an association with timing of first tooth eruption and number of teeth at age one (i.e., it is not in the table above). Each G at increased the odds of requiring orthodontic treatment by 1.35 times.
All of the SNPs identified in this study are in or around genes known to have roles in organ formation, growth and development, or cancer. The authors suggest that studies of teething and other aspects of infant development may have far reaching implications.
&#8220;The discoveries of genetic and environmental determinants of human development will help us to understand the development of many disorders which appear later in life. We hope also that these discoveries will increase knowledge about why fetal growth seems to be such an important factor in the development of many chronic diseases, &#8221; said Professor Marjo-Riitta Jarvelin, the study&#8217;s senior author, in a press release.

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