Genetics

Don’t Regulate DTC Genetic Testing

April 27th, 2011 | No Comments | Source: Commentary

Today, consumers can purchase dozens of medical tests without a prescription–tests that tell them whether they are pregnant, have a urinary infection, their cholesterol is too high, and so on.

Should direct-to-consumer (DTC) genetic tests be as readily available? These are the mail-in saliva tests that tell consumers about their genetic susceptibility to Alzheimer’s disease, type 2 diabetes, heart disease and other conditions.

DTC genetic tests are different from the genetic tests that have been used for decades in prenatal and newborn screening, and more recently in predictive testing (like the BRCA test for breast cancer risk).

The difference is not the substrate being tested. In both cases, it’s DNA. Rather, it’s who owns the testing process.

For the legacy DNA tests, health professionals own the process. As per protocol, they obtain permission (informed consent) from patients before ordering the test. Then, they consult with and support the patient once the results are known.

In contrast, DTC genetic tests transfer ownership of the genetic testing process to consumers. A person can decide for herself whether to get a DTC genetic test. She doesn’t need permission from a provider, and has no obligation to share the information with her provider.

This bothers many physicians, bioethicists and consumer advocates. They point out that DTC genetic test reports can be difficult to interpret (for physicians as well, I might add, despite claims that they are universally qualified to do so). They decry the lack of regulatory oversight of testing facilities which might help assure the accuracy and reliability of the information. Furthermore, reports of “egregious…deceptive marketing” by some DTC genetic testing vendors suggest that consumers maybe harmed, they say.

These people call for regulatory oversight of DTC genetic testing. The FDA has in certain limited instances, already begun to do just that.

Physician organizations tend to support the regulation of DTC genetic testing. In particular, they favor rules that transfer ownership of DTC genetic testing to (guess who?) physicians who can then serve as custodians of the information, just as they do for the traditional genetic tests mentioned above.

Set the Data Free
I disagree. People who want access to their genetic-risk information should be free to pay their own money to obtain it, period. The only place where regulation has a role in DTC genetic testing is to assure the quality of the results being generated. That’s it.

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Rare Form of Dwarfism Protects against Cancer, Diabetes

March 28th, 2011 | No Comments | Source: Science Translational Med., Wall Street Journal

People affected by a rare, inherited form of dwarfism virtually never get diabetes or cancer, scientists have reported. Their findings may someday open up new ways to treat or prevent both conditions.

The scientists are Jaime Guevara-Aguirre, an Ecuadorean physician, and Valter Longo, a cell biologist from USC. They collaborated to study a cohort of about 100 Ecuadoreans that had Laron syndrome, an extremely rare condition caused by a gene mutation that prevents their bodies from responding properly to growth hormone.

Guevara-Aguirre had been following the cohort for more than 2 decades. He and Longo reviewed his notes and found exactly one nonfatal case of cancer and zero cases of diabetes. By comparison, the scientists’ review of 1,600 relatives, who also resided in Ecuador, revealed that 5% of them developed diabetes and 17% developed cancer. These incidence rates matched those found in the general population.

The absence of diabetes was particularly remarkable since the Laron cohort had higher obesity rates than their non-affected relatives, and obesity is a risk factor for the disease.

To figure out why Laron dwarfs almost never got diabetes or cancer, the scientists performed genetic analyses on samples of their blood and saliva. They found that family members with the condition had lower levels of IGF-1 (insulin-like growth factor 1), a chemical that plays a central role in growth during childhood. Laron patients also had lower blood insulin levels and increased sensitivity to insulin. (more…)

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Personalized Medicine for the Treatment of Alcoholism

March 16th, 2011 | 1 Comment | Source: Am. J. Psychiatry, Wall Street Journal

Genetic factors predispose people to alcoholism. That’s why the children of alcoholics are four times more likely to develop drinking problems, and the sons of alcoholic fathers are at even greater risk. And that’s why kids who are born to alcoholic parents and then raised by non-drinking parents have the same risk for alcoholism as if they had been raised by their biologic parents.

This is not to say that one, or even a handful of genes are responsible for the disease. The number is clearly far higher than that. Genes that predispose to alcoholism affect diverse physiological functions ranging from those involved with alcohol metabolism to those governing the behavioral response to rewards and pleasure. Some genes linked primarily to depression have even been linked to alcoholism.

The explanation for this multi-gene etiology is that diverse social and environmental factors can interact with genetically programmed mechanisms in complex ways, all of which end-up precipitating the syndrome.

Gene Links to Alcoholism: A Sampler
The “Asian Flush” genes are perhaps the best understood in this regard. Fully one third of all people of East Asian descent are born with a genetic deficiency that causes their cheeks, and often their necks, arms and trunk to turn sunburn-red after consuming even small amounts of alcohol. This “Asian Flush” syndrome is often associated with nausea, headache and tachycardia, distasteful symptoms which act collectively to deter people from drinking alcohol. The result: very few affected individuals become alcoholics.

A separate, colloquially named “tipsy gene” makes affected individuals feel completely bombed after just a drink or two. As many as 20% of the US population has the tipsy gene. It too seems to protect people from becoming alcoholics.

By contrast, a gene variant for the DRD2 dopamine receptor in the brain causes people to feel downright euphoric after drinking, probably because it alters the way the brain’s reward circuits respond to alcohol. Some (but not all) studies have shown this gene variant to be present in a disproportionate number of alcoholics, drug addicts and cigarette smokers. (more…)

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Asian Flush: What You Don’t Know can Kill You

January 25th, 2011 | 1 Comment | Source: MSNBC, PLoS Medicine

Plenty of folks get a bit red in the face this time of the year. The cheeks of those who live in northern climes may take on a certain glow when they walk the dog or take out the garbage on a brisk, windy night. The same appearance bedevils folks in warmer climes should they forget to apply sunblock before settling beside the pool.

An altogether different group includes fully one third of all people of East Asian descent, who have been born with a genetic deficiency that causes their cheeks, and often their necks, arms and trunk to turn sunburn-red after consuming even small amounts of alcohol (see picture).

The condition is known colloquially as “Asian Flush” or “Asian Glow.” It is often associated with nausea, headache and tachycardia, and is caused by an inherited deficiency of aldehyde dehydrogenase 2 (ALDH2), one of 2 key enzymes involved in the metabolism of alcohol.

Unfortunately, Asian Flush isn’t as benign as once thought. Scientists have determined in recent years that ALDH2 deficiency is a risk factor for esophageal cancer, which happens to be one of the deadliest cancers humans can get.

Philip Brooks and colleagues at the National Institute on Alcohol Abuse and Alcoholism published a seminal article on this association in 2009. In it, the scientists explained that the first of those 2 key enzymes transforms alcohol into acetaldehyde, a vasodilator in the short term and a carcinogen in the long term. The second enzyme, ALDH2, converts that toxin into acetate, a harmless chemical.

People who lack ALDH2 experience a build-up of acetaldehyde in the body after they consume alcohol. The short-term effect of the build-up is the Asian Flush.

But that’s not what prompted Brooks to write that article. “People with this ALDH2 deficiency have a really high risk of getting esophageal cancer when they drink alcohol,” he explained to the LA Times. “Anyone who drinks is at risk, but the more you drink, the more your risk goes up. And when you’re ALDH2-deficient, your risk goes up much more dramatically.” (more…)

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Gene Therapy for Depression

November 26th, 2010 | 1 Comment | Source: BurrillReport, Science Translational Med.

Gene therapy involves replacing or altering a small part of DNA whose abnormal expression causes a disease. The new therapeutic technique has shown promise for the treatment of cystic fibrosis, hemophilia and muscular dystrophy. Now, according to scientists at Weill Cornell Medical Center, perhaps depression should be added to this list as well.

In mice that is. Perhaps someday gene therapy can be used to treat humans as well.

That’s the suggestion made by Michael Kaplitt and colleagues in their write-up summarizing the results of their recent experiments which appears in Science Translational Medicine.

Kaplitt’s team knew that abnormalities in a particular region of the brain-the nucleus accumbens-were associated with depression in humans and behaviors akin to depression in mice (specifically, murine responses to rewards and pleasurable experiences). They knew that the problem in the nucleus accumbens had to do with abnormalities in the way the neurotransmitter serotonin impacted chemical pathways that mediated mood, appetite and sleep patterns. And they knew that most antidepressant drugs acted to regulate serotonin metabolism in the brain.

Kaplitt’s group went from there to isolate the problem with serotonin metabolism in the nucleus accumbens of “depressed” mice. It turned out to be the lack of a single protein, known as p11, which normally serves to transport serotonin receptors to the surface of nerve cells. When p11 was missing or didn’t work properly, nerve cells could produce adequate amounts of serotonin receptors, but the receptors never made it to the surface of the nerve cell membrane where they could bind serotonin and thus trigger normal behavioral responses.

Kaplitt’s team then used somatic gene transfer (that is, “gene therapy”) to replace the gene responsible for producing the defective p11 protein in the nucleus accumbens of their depressed mice. They subsequently observed that the depressive symptoms disappeared.

“We potentially have a novel therapy to target what we now believe is one root cause of human depression,” Kaplitt told BurrillReport. Kaplitt’s team hopes to launch a clinical trial of gene therapy in humans with depression sometime soon.

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Why Autism is More Common in Boys

November 15th, 2010 | 1 Comment | Source: BurrillReport

Toronto-based scientists have found that boys with a specific DNA mutation on their X-chromosomes are at high risk of developing Autism Spectrum Disorder (ASD).

To reach these conclusions, John Vincent and colleagues at the Centre for Addiction and Mental Health compared the gene sequences of 2,000 people with ASD with a control group that had no behavioral or intellectual limitations.

The scientists found that about 1% of boys with ASD also had mutations in a gene known as PTCHD1, which is located on the X-chromosome. The scientists did not find these mutations in boys who were in the control group.

“We believe the PTCHD1 gene has a role in a neurobiological pathway that delivers information to cells during brain development–this mutation may disrupt crucial developmental processes, contributing to the onset of autism,” Vincent told BurrillReport. “Our discovery will facilitate early detection (and) increase the likelihood of successful interventions.”

ASD is a neurological condition associated with abnormal social interaction and communication, unusual behaviors, and frequently, diminished intelligence. It affects about one in 240 girls and one in 70 boys. The causes of ASD remain unknown, though scientists have long suspected that genetic factors play a role.

Boys inherit an X-chromosome from their mothers and a Y-chromosome from their fathers. If a boy’s lone X-chromosome lacks a normally functioning PTCHD1 gene, he is at risk for ASD or some other intellectual disability, the scientists explained. Girls inherit an X-chromosome from their mothers and fathers, so the effects of a PTCHD1 gene defect in one X-chromosome are masked by the normally functioning gene on the other X-chromosome. These girls will not develop ASD, but their male offspring are at risk.

The study appears in Science Translational Medicine. 

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Genetically Engineered Salmon

October 25th, 2010 | No Comments | Source: BurrillReport

An FDA advisory panel has recommended that the agency approve a Massachusetts-based company’s plans to commercialize its genetically-engineered salmon, which grow to adult size nearly twice as fast as their natural-born counterparts.

If the FDA follows the recommendations of the Veterinary Medicine Advisory Committee, the modified salmon will be the first such animal to be marketed in the US.

The Committee is comprised largely of veterinary scientists. It concluded that the new salmon was safe to eat and that the process used to grow it would not pose a significant threat to the environment.

The FDA is not required to follow the recommendations of its advisory panels. It will probably take months before deciding the matter.

Waltham-based AquaBounty has been working on its AquAdvantage Atlantic salmon for over a decade. They grow quickly because company scientists inserted genes encoding for growth hormone from both the Chinook salmon and an eel-like creature known as the ocean pout into their DNA.

The modified fish produce growth hormone year-round. Native Atlantic salmon don’t produce the stuff, and hence don’t grow, each winter. The AquAdvantage salmon end-up being sterile females, for the most part.

AquaBounty plans to grow its genetically-modified salmon in inland tanks to prevent them from interacting with native species. “The possibility of an escape or an event with any possibility to interact with the wild population is infinitesimal,” Ronald Stotish, AquaBounty’s CEO told BurrillReport.

By the way, the Advisory Committee suggested that the FDA monitor the environmental impact of AquaBounty’s commercial operations if they are approved, and that consumers be appraised about what they are buying. Current FDA rules ban labeling that is based exclusively on how foods are produced.

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The Wild West of Genetic Testing

September 7th, 2010 | No Comments | Source: Washington Post

Last month, a mix-up at the genetic testing company 23andMe caused 87 people to receive incorrect results. In one case, a woman was told her son carried genes for a life-threatening disorder when in fact, he didn’t. Another woman who thought she was white, was told her genes resembled those of an African American. In a third case, an actual woman was told she was a man.

23andMe said it regreted the mishap, spotted the error, notified people quickly, and took steps to assure the problem wouldn’t happen again.

The gaffe has focused attention on the question of whether the government should begin to regulate the burgeoning genetic testing industry more aggressively.

Supporters of this view argue that some companies in the space have made claims that are not supported by fact, and that the results of genetic testing are too complicated for people to interpret by themselves. People who are told they don’t have genes that put them at very high risk for developing breast cancer might stop getting mammograms, for example.

The flip-side to the argument is that a heavy dose of regulation might stifle innovation and render the tests too expensive and unnecessarily difficult to access. In addition, it’s far from clear that the FDA has the resources to verify the complex scientific claims being made by genetic testing companies.

Amid the debate, the FDA has begun to intervene. This spring, it blocked an effort by Pathway Genomics to market genetic tests in drug stores. Soon thereafter, it notified 5 companies that were marketing testing kits over the Internet that their tests were medical devices which needed to pass through normal regulatory processes.

Despite these early interventions, genetic testing remains in the Wild West phase of commercial development. Caveat emptor.

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Genes and Longevity

August 16th, 2010 | No Comments | Source: NY Times, Science

Boston University scientists claim to have identified a small set of genetic variants that predicts extreme longevity.

The scientists, Paola Sebastiani and Thomas Perls, examined the DNA of 1,055 centenarians living in New England. They isolated 150 gene variants that were common in this population. They subsequently examined a separate sample of centenarians and found that 77% of them had many of the same genetic variants.

The centenarians in the original cohort had as many disease-associated gene variants as shorter-lived people, so the scientists reasoned that the genes they identified must protect against disease.

This conclusion is at odds with current thinking about extreme longevity which is predicated on the assumption that long life is caused by the absence of disease-causing gene variants, rather than the presence of protective genes.

To find the protective genes, the scientists implemented a genome-wide association study, a technique that has so far failed to meet expectations that it would unlock genetic secrets behind common conditions like diabetes and Alzheimer’s disease.

Some scientists questioned the findings of the BU group. Kari Stefansson, a geneticist who works for Decode Gentics told the New York Times for example, that he was “amazed at how many loci of genome-wide significance have been found in a modest sample size.”

Stefansson’s company has also studied extreme longevity. Apparently, none of the BU group’s 150 genetic variants showed up in the population studied by Decode Genetics.

There are roughly 80,000 centenarians in the US right now. Roughly 15 % of the general population has some or many of the 150 genetic variants found in the BU study. Most of them fail to reach a ripe old age because of accidents or an unhealthy lifestyle.

Their report appears in Thursday’s issue of Science.

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Genes Predict Longevity

July 20th, 2010 | No Comments | Source: NY Times, Science

Boston University scientists claim to have identified a small set of genetic variants that accurately predicts extreme longevity in humans.

dna spiralThe scientists, Paola Sebastiani and Thomas Perls, examined the DNA of 1,055 centenarians living in New England. They isolated 150 gene variants that were common in this population. They subsequently examined a separate sample of centenarians and found that 77% of them had many of the same genetic variants.

The centenarians in the original cohort had as many disease-associated gene variants as shorter-lived people, so the scientists reasoned that the genes they had identified must protect against disease.

This conclusion is at odds with current thinking about extreme longevity which is predicated on the assumption that long life is caused by the absence of disease-causing gene variants, rather than the presence of protective genes.

To find the protective genes, the scientists implemented a genome-wide association study, a technique that had previously failed to meet expectations that it could unlock genetic secrets behind common conditions like diabetes and Alzheimer’s disease.

Some scientists questioned the findings of the BU group. Kari Stefansson, a geneticist who works for Decode Gentics, told the New York Times for example that he was “amazed at how many loci of genome-wide significance have been found in a modest sample size.”

Stefansson’s company has also studied extreme longevity. Apparently, none of the BU group’s 150 genetic variants showed up in the population studied by Decode Genetics.

There are roughly 80,000 centenarians in the US right now. Roughly 15 % of the general population has some or many of the 150 genetic variants found in the BU study. Most of them fail to reach extreme old age because of accidents or an unhealthy lifestyle.

The report appears in Science.

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