13 Things to Know About DNA Testing Kits

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The search for our identities—where we came from, what we're made of—is a unifying human experience, and our collective fascination with ourselves as individuals has fueled a booming industry around personal DNA testing. More than 12 million people have had their DNA tested by services like 23andMe and AncestryDNA, and that number is expected to grow substantially in the next few years. But can DNA tests really reveal the nuanced information about ancestry and health that many of us seek? Here are 13 things to know about these personal testing kits.

1. PERSONAL DNA TESTING IS SIMPLE—ALL IT TAKES IS A LITTLE SPIT.

Typically, all you have to do is collect some of your saliva or swab the inside of your cheek, then seal the sample in a container and mail it to the lab in a pre-labeled envelope or box. Six to eight weeks later, you can see the results online.

Most personal DNA tests are relatively affordable: Kits from industry leaders like 23andMe, AncestryDNA, Family Tree DNA, MyHeritage DNA, and Living DNA range from $69 to $199. In some cases, the price depends on which genetic reports a customer opts to receive: For 23andMe, for instance, a test that only aims to analyze your ancestry is cheaper than one that also includes health information. Check out this Wiki chart from the International Society of Genetic Genealogy to compare companies' offerings.

2. THE KITS LOOK FOR GENETIC VARIATIONS CALLED SINGLE NUCLEOTIDE POLYMORPHISMS.

After extracting DNA from your cheek swab or saliva sample, DNA testing companies search your DNA for certain genetic variants. The building blocks of DNA are chemical bases called nucleotides, which come in four varieties—A, T, C, and G (adenine, thymine, cytosine, and guanine, respectively). We have 3 billion pairs of these bases, so 6 billion letters in all, strung together in a sequence. Altogether, this genetic information is called your genome.

DNA testing companies determine which of the four letters is present at many locations in your genome. Much of the sequence is shared among humans, so the companies focus on specific letters that vary from person to person, known as single nucleotide polymorphisms (SNPs). Many SNPs have some biological relevance. For example, having one variant of a specific SNP near the gene OCA2, which codes for a protein believed to be involved in producing the dark pigment melanin, makes it much more likely you’ll have blue or green eyes. Other traits and even some diseases are also associated with certain SNPs, some more strongly than others.

3. KIT ACCURACY CAN VARY BASED ON TESTING METHODS.

According to company spokesperson Scott Hadly, 23andMe can identify SNPs with 99.9 percent accuracy, which is in a plausible range for the methods they use. Since many other major companies use similar techniques, their accuracy may be about equivalent—but not all tests meet the same standards. Recently, one test failed to recognize that a purportedly human DNA sample actually came from a golden retriever named Bailey. It did recommend, though, that based on her genetics, Bailey should take up cycling and basketball. The canine’s results came from the lighthearted Superhero DNA Test, which claims to tell customers about their strength, speed, and intelligence. It only tests for four genetic variants, while the pricier kits can include tens of thousands of variants. (It's also worth noting that no matter how many variants a kit tests for, it can't predict complex traits like intelligence, which are influenced by many different genes and environmental factors.)

You should steer clear of companies that offer dubious predictions about your optimal diet, what sports you'll be good at, and other questionable tips. Experts say using DNA tests to extrapolate this information is at best premature and at worst pseudoscience, especially because the recommendations are often based on just a handful of studies on specific groups of people, commonly white men. "The results that have been acquired in one population are not always generalizable to other populations," Jason Rosenbaum, an assistant professor at the University of Pennsylvania's medical school, tells Mental Floss.

4. DNA CAN REVEAL GENETIC CONNECTIONS—BUT INFORMATION ON SOME POPULATIONS IS LIMITED.

Companies use various methods to determine ancestry, but the tests generally involve comparing the customer's DNA to reference DNA meant to represent populations from different geographical regions. Since most people have at least somewhat mixed heritage, ancestry is often represented in percentages: 26 percent Polish, 14 percent Greek, and so on.

These tests aren’t able to guarantee where your ancestors actually lived—they can’t directly compare your data to DNA from people who lived hundreds of years ago, as Adam Rutherford, a British geneticist, pointed out to Gizmodo. And not all groups of people are equally represented in the reference populations, which can impact how precise your results are. People with European backgrounds are overrepresented in the reference data, while there are fewer references relevant to those whose roots lie in the Middle East or Asia, for example. But as research is done on a more diverse range of people, companies are tweaking their analyses to provide more detailed ancestry information to people from all over the world.

5. SOME HINT AT YOUR DNA'S DISTANT HISTORY—INCLUDING NEANDERTHAL HERITAGE.

All humans alive today can trace their mitochondrial lineage back to one woman nicknamed Mitochondrial Eve, who may have lived in Africa about 150,000–200,000 years ago (although this is a source of perennial debate). She wasn't the first modern human woman or the only woman living at the time; other women from her time also have descendants today. They just don’t have an unbroken line of female descendants like Mitochondrial Eve does.

We inherit our mitochondria—the parts of our cells that make energy—from our mothers. Some companies offer a mitochondrial DNA test that allows you to find your maternal haplogroup, which includes people who all share a maternal ancestor thousands or tens of thousands of years ago.

Men can learn about their paternal line through the Y chromosome, which is passed from father to son; certain SNPs on the Y chromosome can be used to determine a person's paternal haplogroup. (Women can find their paternal haplogroup through their biological father or brother.) There’s a "Y-chromosomal Adam," too, although scientists disagree about whether he lived around the same time as Mitochondrial Eve.

A home DNA test might even tell you that you're a little bit Neanderthal, which is especially common in Caucasian and Asian people. Don't worry about Neanderthals' reputation as dull brutes. We now know they were intelligent, used tools, and had their own complex culture.

6. YOU COULD FIND RELATIVES YOU DIDN'T KNOW YOU HAD.

Many DNA testing services allow customers to see whether other users of the same service are biologically related. This can be a boon for anyone assembling a detailed family tree, as well as any adoptees wondering about their biological families. Several people have discovered siblings they never knew they had through these services. In one case, two women—one adopted through an agency and another adopted by a family who found her in the woods as a baby—realized they were long-lost sisters.

Not everyone is pleased to uncover family secrets, though, and you should proceed with caution before you allow a company to match you with new relatives.

7. DNA TESTS CAN REVEAL HEALTH INFORMATION …

While genetic testing might reveal your inability to detect the unique odor of asparagus pee, most people are seeking deeper information, such as whether they have genetic variants associated with diseases like Alzheimer's or breast cancer.

Genetic risk is all about probability. For example, it may be frightening to learn you have an SNP associated with a tenfold increase in risk for a disease—but if that disease only affects 0.01 percent of people, your risk is still just 0.1 percent. Even if you have a SNP strongly associated with a more common illness and show signs of having it, you should see a doctor to get a proper evaluation.

And having a disease-associated SNP isn't a diagnosis. Rare variants are especially likely to lead to false positives: if a variant is only found in one in a million people, it’s more likely that the positive test result is an error than it would be with a more common variant. Some companies report on genetic variants that doctors and scientists haven't deemed medically useful to test for—which is why combing over every SNP is of dubious use. Shoumita Dasgupta, an associate professor in the biomedical genetics program at Boston University, tells Mental Floss that healthcare providers often don't order tests for these SNPs "because professionals have come to the conclusion that the predictive value of these tests is limited."

8. … INCLUDING YOUR RISK OF CERTAIN KINDS OF CANCER.

In March 2018, the FDA granted 23andMe permission to give customers information about certain mutations in the genes BRCA1 and BRCA2 that dramatically increase the risk for breast and ovarian cancer. Some people with a faulty BRCA gene take precautions to prevent or detect cancer early, including undergoing preventive double mastectomies, as Angelina Jolie famously did in 2013.

An important caveat: This test only screens for three SNPs in the BRCA genes that are connected to a dramatic increase in the risk of developing cancer. A positive result merits a consultation with doctor, but a negative result doesn't necessarily mean you're free from the risk of cancer, hereditary or not.

9. SOME DNA TESTING KITS ARE PRESCRIPTION ONLY.

GeneSight is designed to reveal what psychiatric medications will work best for a particular patient. Fertilome aims to show whether a person has genetic markers associated with increased risk of fertility problems, and is intended to help people make reproductive decisions such as whether to freeze eggs or try another round of in vitro fertilization. However, both Fertilome and GeneSight have faced criticism from experts who say there's not enough evidence that the tests are clinically valuable. They're also expensive: Fertilome costs $950, while GeneSight can cost several hundred dollars (though the price can drop to zero with certain insurance plans).

10. MORE DATA ISN'T ALWAYS BETTER.

With the price of DNA analysis falling rapidly, some companies are offering to analyze the order of all the letters of a customer's DNA—what's called sequencing—rather than just looking at SNPs. Sequencing is important in research and medicine: Dasgupta says she now sees some physicians ordering full sequences of multiple genes or even whole exomes (the protein-coding sequences in the genome) for patients.

Exome sequencing is useful to doctors and scientists because it allows them to look for genetic variants beyond the commonly tested SNPs. But every test has a risk of generating false positives, so excessive testing means an increased risk that a person will receive an incorrect diagnosis. Rosenbaum likens it to MRIs. "It's one reason why we don't just give MRIs to everyone, because you're going to turn up things that lead you to believe there's disease where there isn't disease," he explains.

11. YOUR DNA RESULTS COULD CONTRIBUTE TO RESEARCH.

Some home DNA testing companies ask customers to participate in research, answering questions about everything from their sleep habits to their personalities. The goal is to discover previously unknown associations between genetic variants and specific traits. "The way many genetic studies are designed, the more people who are recruited to the study, the more likely the study will be able to identify genetic factors that impact the trait or condition being studied," Dasgupta says.

Personal DNA testing companies potentially have access to the genetic data of millions of users, giving them a huge opportunity to make these connections. Using customer-provided data, 23andMe has already reported some preliminary discoveries on genetic variants linked to detached earlobes, the risk of Parkinson's disease, and more. Studies based on self-reported information always come with caveats, but they’re common in many fields of research and especially useful when collecting objective data isn't practical or possible. Future research spurred by these observations will reveal whether crowdsourced research like 23andMe's has potential to become part of geneticists' repertoire.

12. YOU COULD POTENTIALLY EARN MONEY FROM YOUR DNA.

One company, Genos, charges $499 to sequence a customer's entire exome, and then offers to connect them with genetic researchers. Participating research partners can offer $50 to $250 to Genos users for completing a study intended to find links between their genetic information and any trait or condition the researchers are studying, including dementia, cancer, and infectious disease. Meanwhile, the newly formed company Nebula proposes to sequence customers' genomes, secure them with blockchain technology, and allow customers to control the data—including selling it to biotech and pharmaceutical companies in exchange for Bitcoin-like cryptocurrency. There’s still potential for privacy issues, however, since there’s no guarantee companies that rent or purchase genetic data will keep it secure.

13. YOUR DNA MIGHT ONE DAY HELP TO CATCH A CRIMINAL.

Recently, police investigators in California arrested a man suspected to be the Golden State Killer, thought to be responsible for dozens of rapes and burglaries and at least 12 murders in California from 1976 to 1986. The suspect left DNA behind at the scene of a 1980 murder; after having the DNA analyzed, the investigators created a fake profile on the genealogy website GEDMatch and uploaded the data, hoping it would turn up some of the killer's relatives. It did—and with the help of genealogy experts, the investigators followed the genetic trail to the Sacramento home of 72-year-old Joseph James DeAngelo, who was a cop during the first several years of the deadly crime spree.

The case has raised ethical and privacy concerns for some experts. Genetic data can be stored indefinitely, and it’s possible to use a person's DNA to make inferences about biological relatives who haven’t even taken DNA tests.

Some Mathematicians Think the Equal Sign is On Its Way Out

Paperkites/iStock via Getty Images
Paperkites/iStock via Getty Images

A growing number of mathematicians are skeptical that the equal sign, traditionally used to show exact relationships between sets of objects, holds up to new mathematical models, WIRED reports.

To understand their arguments, it’s important to understand set theory—a theory of mathematics that’s been around since at least the 1870s [PDF]. Take the classic formula 1+1=2. Say you have four pieces of fruit—an apple, an orange, and two bananas—and you put the apple and the orange on one side of a table and the two bananas on the other. In set theory, that’s an equation: One piece of fruit plus one piece of fruit on the left side of the table equals two pieces of fruit on the right side of the table. The two sets, or collections of objects, are the same size, so they’re equal.

But here’s where it gets complicated. What if you put an apple and a banana on the left side of the table and an orange and a banana on the other side? That’s clearly different from the first scenario, but set theory writes it as the same thing: 1+1=2. What if you switched the order of the first set of objects, so instead of having an apple and an orange, you had an orange and an apple? What if you had only bananas? There are potentially infinite scenarios, but set theory is limited to expressing them all in only one way.

“The problem is, there are many ways to pair up,” Joseph Campbell, a mathematics professor at Duke University, told Quanta Magazine. “We’ve forgotten them when we say ‘equals.’”

A better alternative is the idea of equivalence, some mathematicians say [PDF]. Equality is a strict relationship, but equivalence comes in different forms. The two-bananas-on-each-side-of-the-table scenario is considered strong equivalence—all of the elements in both sets are the same. The scenario where you have an apple and an orange on one side and two bananas on the other? That’s a slightly weaker form of equivalence.

A new wave of mathematicians is turning to the idea of category theory [PDF], which is based in understanding the relationships between different objects. Category theory is better than set theory at dealing with equivalence, and it’s also more universally applicable to different branches of mathematics.

But a switch to category theory won’t come overnight, according to Quanta. Interpreting equations using equivalence rather than equality is much more complicated, and it requires relearning and rewriting everything about mathematics—even down to algebra and arithmetic.

“This complicates matters enormously, in a way that makes it seem impossible to work with this new version of mathematics we’re imagining,” mathematician David Ayala told Quanta.

Several mathematicians are at the forefront of category theory research, but the field is still relatively young. So while the equal sign isn’t passé just yet, it’s likely that an oncoming mathematical revolution will change its meaning.

[h/t Wired]

7 Facts About Blood

Moussa81/iStock via Getty Images
Moussa81/iStock via Getty Images

Everyone knows that when you get cut, you bleed—a result of the constant movement of blood through our bodies. But do you know all of the functions the circulatory system actually performs? Here are some surprising facts about human blood—and a few cringe-worthy theories that preceded the modern scientific understanding of this vital fluid.

1. Doctors still use bloodletting and leeches to treat diseases.

Ancient peoples knew the circulatory system was important to overall health. That may be one reason for bloodletting, the practice of cutting people to “cure” everything from cancer to infections to mental illness. For the better part of two millennia, it persisted as one of the most common medical procedures.

Hippocrates believed that illness was caused by an imbalance of four “humors”—blood, phlegm, black bile, and yellow bile. For centuries, doctors believed balance could be restored by removing excess blood, often by bloodletting or leeches. It didn’t always go so well. George Washington, for example, died soon after his physician treated a sore throat with bloodletting and a series of other agonizing procedures.

By the mid-19th century, bloodletting was on its way out, but it hasn’t completely disappeared. Bloodletting is an effective treatment for some rare conditions like hemochromatosis, a hereditary condition causing your body to absorb too much iron.

Leeches have also made a comeback in medicine. We now know that leech saliva contains substances with anti-inflammatory, antibiotic, and anesthetic properties. It also contains hirudin, an enzyme that prevents clotting. It lets more oxygenated blood into the wound, reducing swelling and helping to rebuild tiny blood vessels so that it can heal faster. That’s why leeches are still sometimes used in treating certain circulatory diseases, arthritis, and skin grafting, and helps reattach fingers and toes. (Contrary to popular belief, even the blood-sucking variety of leech is not all that interested in human blood.)

2. Scientists didn't understand how blood circulation worked until the 17th century.

William Harvey, an English physician, is generally credited with discovering and demonstrating the mechanics of circulation, though his work developed out of the cumulative body of research on the subject over centuries.

The prevailing theory in Harvey’s time was that the lungs, not the heart, moved blood through the body. In part by dissecting living animals and studying their still-beating hearts, Harvey was able to describe how the heart pumped blood through the body and how blood returned to the heart. He also showed how valves in veins helped control the flow of blood through the body. Harvey was ridiculed by many of his contemporaries, but his theories were ultimately vindicated.

3. Blood types were discovered in the early 20th century.

Austrian physician Karl Landsteiner discovered different blood groups in 1901, after he noticed that blood mixed from people with different types would clot. His subsequent research classified types A, B and O. (Later research identified an additional type, AB). Blood types are differentiated by the kinds of antigens—molecules that provoke an immune system reaction—that attach to red blood cells.

People with Type A blood have only A antigens attached to their red cells but have B antigens in their plasma. In those with Type B blood, the location of the antigens is reversed. Type O blood has neither A nor B antigens on red cells, but both are present in the plasma. And finally, Type AB has both A and B antigens on red cells but neither in plasma. But wait, there’s more! When a third antigen, called the Rh factor, is present, the blood type is classified as positive. When Rh factor is absent, the blood type is negative.

Scientists still don’t understand why humans have different blood types, but knowing yours is important: Some people have life-threatening reactions if they receive a blood type during a transfusion that doesn’t “mix” with their own. Before researchers developed reliable ways to detect blood types, that tended to turn out badly for people receiving an incompatible human (or animal!) blood transfusion.

4. Blood makes up about 8 percent of our total body weight.

Adult bodies contain about 5 liters (5.3 quarts) of blood. An exception is pregnant women, whose bodies can produce about 50 percent more blood to nourish a fetus.)

Plasma, the liquid portion of blood, accounts for about 3 liters. It carries red and white blood cells and platelets, which deliver oxygen to our cells, fight disease, and repair damaged vessels. These cells are joined by electrolytes, antibodies, vitamins, proteins, and other nutrients required to maintain all the other cells in the body.

5. A healthy red blood cell lasts for roughly 120 days.

Red blood cells contain an important protein called hemoglobin that delivers oxygen to all the other cells in our bodies. It also carries carbon dioxide from those cells back to the lungs.

Red blood cells are produced in bone marrow, but not everyone produces healthy ones. People with sickle cell anemia, a hereditary condition, develop malformed red blood cells that get stuck in blood vessels. These blood cells last about 10 to 20 days, which leads to a chronic shortage of red blood cells, often causing to pain, infection, and organ damage.

6. Blood might play a role in treating Alzheimer's disease.

In 2014, research led by Stanford University scientists found that injecting the plasma of young mice into older mice improved memory and learning. Their findings follow years of experiments in which scientists surgically joined the circulatory systems of old and young mice to test whether young blood could reverse signs of aging. Those results showed rejuvenating effects of a particular blood protein on the organs of older mice.

The Stanford team’s findings that young blood had positive effects on mouse memory and learning sparked intense interest in whether it could eventually lead to new treatments for Alzheimer’s disease and other age-related conditions.

7. The sight of blood can make people faint.

For 3 to 4 percent of people, squeamishness associated with blood, injury, or invasive medical procedures like injections rises to the level of a true phobia called blood injury injection phobia (BII). And most sufferers share a common reaction: fainting.

Most phobias cause an increase in heart rate and blood pressure, and often muscle tension, shakes, and sweating: part of the body’s sympathetic nervous system’s “fight or flight” response. But sufferers of BII experience an added symptom. After initially increasing, their blood pressure and heart rate will abruptly drop.

This reaction is caused by the vagus nerve, which works to keep a steady heart rate, among other things. But the vagus nerve sometimes overdoes it, pushing blood pressure and heart rate too low. (You may have experienced this phenomenon if you’ve ever felt faint while hungry, dehydrated, startled, or standing up too fast.) For people with BII, the vasovagal response can happen at the mere sight or suggestion of blood, needles, or bodily injury, making even a routine medical or dental checkup cause for dread and embarrassment.

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