Our Genes Multitask

"Pond slime oozing along the surface of a creek," William J. Cromie of the Harvard University Gazette once noted, "has 200 times as much DNA as Albert Einstein or Stephen Hawking."

Ever since DNA was discovered about 60 years ago, scientists have been perplexed by the finding that we humans, presumably the most complex of all living creatures on earth, have relatively little of it. We have fewer genes than many other species. 

What is a gene? Genes are strands of DNA that serve as a pattern for stands of RNA that code the creation of proteins. These proteins may be enzymes. They may become structural components. They may become hormones. Genetic expression is a complicated process; genes may be epigenetically turned on and turned off.  The bottom line, the more complex processes there are in an organisms, the greater the expected genetic activity.

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To be sure, we humans with our 22,333 genes have more DNA than a flu virus (11 genes) or E. coli (4,149 genes) or a chicken (16,736 genes), but we have less DNA than grapes (30,434 genes) or the amoebas in pond slime (about 4 million genes). Let's assume that people aren't just more complicated than chickens, they are also more complicated than slime. How can it be that humans have so few genes? And what are the practical implications of this reality?

The Importance of Genes That Have Multiple Functions

In a study published in the prestigious journal Nature Genetics, researchers at the New York Genome Center and the genetic testing company 23 and me have announced analyses of the complete DNA of thousands of people that indicate that genes code proteins for more than one purpose. For nearly 60 years, scientists have plodded along guided by the assumption that one gene influences just one trait. The analysis of samples from 23 and me tests has revealed that single genes may determine multiple traits. For instance:

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• The same gene determines when you will reach puberty, how tall you are, whether you will develop male pattern baldness, and what your BMI will be.
• The same gene that increases your risk of inflammatory bowel disease increases your risk of schizophrenia.
• The same gene that determines how well your body absorbs zinc from food also influences your risk for both schizophrenia and Parkinson's disease.
• The same gene determines whether you will have type 2 diabetes and whether you will develop Alzheimer's.
• The same gene determines whether you will have allergies, whether you will have Parkinson's disease, and whether you will develop a sun allergy that causes you to sneeze when the sun is out.

Connecting and Potentially Curing Diabetes and Alzheimer's with a Multitasking Gene

Obviously, the New York Genome Center couldn't go to the National Institutes of Health and ask for millions of dollars to study the question whether a gene will make you sneeze on a sunny day. However, since 23 and me already had complete copies of the DNA of thousands of people and information on their disease conditions, the Genome Center simply had to analyze the data provided by the public.

All of this is very interesting, but why do we care that genes multitask? Does this fact make a difference in health? Will there ever be any practical application of this research? There already is.

If the same gene causes different diseases, then different diseases might have the same treatment. There may already be cures for diseases that simply haven't been tried because no one supposed that they developed from the same underlying, genetic processes that cause conditions that appear to be very different. This means that a treatment for sun allergies just might make a big difference in treating Parkinson's disease. Or that a treatment for obesity might reveal the formula for a hair growing tonic. And the connection between diabetes and Alzheimer's has already led to insights into the prevention of Alzheimer's with a diabetes diet.

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In the 1990's, a researcher named Jose Luchsinger at Columbia University in New York City explored the idea that diet might have an influence on Alzheimer's disease. He recruited 980 men and women who were over the age of 65 and followed them for four years. He also asked them for information about their diets. Over the four years of study, 202 of the volunteers were diagnosed with Alzheimer's. The relationship between diet and Alzheimer's turned out to have a genetic connection.

• Some of the volunteers had variations 2 or 3 of a gene called apolipoprotein E. How many calories they ate and how much fat they ate had no relationship to whether they developed Alzheimer's disease.
• Some of the volunteers had variation 4 of the apolipoprotein E epsilon4 gene. Those in the top 25 percent of calorie and fat consumption had up to 390 percent greater risk of developing Alzheimer's compared to those in the bottom 25 percent.

If you had variations 2 or 3 of the gene, then diet didn't really cause Alzheimer's are protect you from it. If you had variation 4, then high-calorie or high-fat diet could greatly increase your risk of the brain disease.

However, later scientists learned that it wasn't just Alzheimer's that was related to this gene, and different variations of this gene required totally different plans of action.

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• People with variation 2 of the apolipoprotein E gene tend to have high levels of triglycerides. Normally, doctors tell them to cut down on their intake of fat. However, if people who have this variation of the gene lower fat consumption, they increase their body's production of a kind of LDL cholesterol that causes heart attacks. For people with this variation of the gene, low-fat diets are potentially deadly, and higher-fat diets are potentially healthy.
• Even when people with variation 4 of this gene avoid Alzheimer's disease, they are at increased risk of heart disease. Their bodies produce fewer triglycerides when their diets contain less fat. They need a low-fat diet not just to prevent Alzheimer's disease but also to prevent heart disease. However, a low-fat diet for someone who does not have this variation of this gene can actually increase the risk of cardiovascular disease, and won't protect against Alzheimer's.

One gene can have multiple functions. Variations in that gene can affect multiple disease patterns. And failing to take genetics into consideration when prescribing medications and diets can cause multiple medical errors. Whenever your doctor offers genetic testing to determine the right treatment, say yes.