Genetic screenings are no replacement for medical advice

Can spit really tell you spit about your health?

A simple sample of saliva is all it takes for commercial DNA researchers to say whether you're likely to get certain diseases, from diabetes to colon cancer to restless leg syndrome. Armed with that knowledge, it's up to you what steps to take next: Steer clear of the buffet table?

Exercise more? Get to the doctor for that checkup you've been avoiding?

All good ideas. Just remember that these commercial genetic screenings shouldn't be seen as serious medical advice, say those working in the rapidly evolving field of genomics.

The companies challenging consumers to take charge of their health with a personal genome test that costs $250 to $1,000 are the same as those gaining recent attention for identifying the ethnic roots of many celebrities.

Although shows such as "Faces of America" and "Who Do You Think You Are" offer broad and harmless clues about genealogical ties, geneticists and medial ethicists say the health tests could persuade a person to undergo a preventive medical procedure to lower the risk of getting a disease to which he or she is predisposed.

"I worry that people will take actions that will be hard to reverse," says Dr. Muin Khoury, director of the National Office of Public Health Genomics at the Centers for Disease Control and Prevention.

It has been less than a decade since scientists completely identified the genetic sequence within a single human body - no small feat, considering there are 20,500 genes marking more than 3 million base pairs of DNA. The CDC estimates researchers have located more than 100 diseases within these genetic hieroglyphics.

Concern that people will take drastic measures is based on the reaction many have had to more established genetic tests conducted by physicians. That includes women found to have a genetic tie to breast cancer, such as actress Christina Applegate, who have opted to undergo chemotherapy and a mastectomy. In fact, a study released last week revealed that the long-term survival of such women may not improve when they opt to remove their breast.

"There's a lot of potential for havoc," says Bill Allen, director of the bioethics and medical professionalism at the University of Florida's College of Medicine. "It can affect decision-making in ways that can be hazardous."

Companies such as 23andMe, Navigenics and DeCodeMe make it clear in online marketing that they don't offer medical advice when assessing genetic risks for conditions such as diabetes, macular degeneration or Parkinson's disease. Instead, individuals can use the information to alter behaviors or prepare for a possible onset, a spokesman for 23andMe says.

"We believe that the more information a person can have about their body, including sensitivity to particular drugs, which diseases they're carriers for and their genetic risks for particular conditions, the more empowered they'll be to make sound health decisions together with their physician or other medical provider," a spokesman said in e-mailed comments.

The scope of diseases assessed in personal genome tests has grown significantly since 23andMe and others emerged in 2007. Consumers don't see it, but scientists analyze the data according to disease, using clues located on a single gene (cystic fibrosis, for example) or on multiple genes and influenced by other behavioral factors such as smoking (such as heart disease).

The companies admit pinpointing risk is difficult. A 2009 study in the journal Nature revealed that identical saliva samples sent to separate companies resulted in conflicting results.

When saliva from five individuals was sent to 23andMe and Navigenics and tested for the relative risk of 13 common diseases, results were inconsistent at least once for nine of the 13 conditions. And three of the five individuals tested received opposite risk results for four
conditions: type 2 diabetes, heart attack, lupus and restless leg syndrome.

Navigenics and 23andMe responded to the study with a jointly written letter that acknowledged that "Genotype-based prediction for common multifactorial disease is still in its infancy. More work must be done to standardize markers used; to better explain to the contribution of genetics to common, complex diseases; and to incorporate common genetic variants into clinical practice."

The developing state of genomics is why family history and personal behaviors are more reliable and far cheaper indicators or future disease risk, says Dr. Rebecca Sutphen, a University of South Florida genetic researcher.

"A geneticist is never going to give you all the information about your risk," says Sutphen, who also is a board member for Informed Medical Decisions, which offers telephone genetics counseling for a growing number of companies, including DeCodeMe. She advocates professional
counseling for anyone who undergoes consumer tests, or individual genetic tests conducted through physicians.

Sutphen, an expert in the BRCA gene linked to breast and ovarian cancer risk, says that particular test is reliable because it targets a small at-risk group and has been conducted 100,000 times. The BRCA gene is a strong factor of cancer risk in about 5 percent of females with a specific family heritage or relatives with cancers at a young age.

This gene is not part of the consumer health tests.

She says she expects the consumer testing to be more reliable - and affordable - in three to five years. That's how fast the science is evolving.

The CDC's Khoury agrees. He likens today's clients of personal genome tests to "parts of the population who want to be the first to buy the 3-D TV." A recent New York Times story estimated that Navigenics and 23andMe have tested 55,000 individuals in the past three years.

As a geneticist with concerns about reliability, Khoury says he has yet to jump on personal genomics bandwagon.

"When the field is stable," he says, "I'll be one of the first people to sign up."

HAPPY DNA DAY
It's not every day you get to celebrate your chromosomal makeup.

April 25 is DNA Day 2010, the National Institutes of Health's attempt to recognize genomic science, starting with the 1953 discovery of DNA's double helix by James Watson and Francis Crick.

Schools across the country will celebrate April 23.

Scientists clearly take the day seriously - sort of. The day's Facebook page links to articles relevant to the topic and promotes online chats for students. But it also highlights the annual double helix photo contest, for which artists build the chromosomal chain out of objects ranging from fortune cookies to colorful Peeps candy.

GENOME TEST
It takes little more than spit and a credit card number to get your genome tested. Here are the basic steps the major commercial companies utilize:

1. Get a kit, usually by ordering online.

2. Swab or spit saliva into a container provided by the company.

3. Ship it off, and wait up to a month.

4. Get results via computer about diseases for which you may be more at risk. Some companies offer a follow-up call with a genetic counselor.

BY THE NUMBERS
We know there's loads of information inside your DNA, but researchers are still scrambling to make sense of the data. Take a look at some of the numbers behind the genome inside every human cell to understand why your genetic instruction manual remains such a massive question mark:

23 pairs of chromosomes

20,500 genes marking the DNA

3.1 billion base pairs of DNA sequence

100 trillion cells in an adult human

Source: National Center for Biotechnology Information