Visiting the Gene Doctor

Tanisha Daniels, 12, is a happy, energetic girl who likes going to the mall and gabbing on the phone–when she’s not sick.

Tanisha has sickle-cell anemia, a disease that causes normally round red blood cells to become sickle-, or crescent-, shaped. Sickle-shaped cells clog blood vessels, causing fatigue and attacks of intense pain, often referred to as pain crises. “The pain that is inflicted on my body when I am in a pain crisis is so overwhelming that I don’t know what to compare it to,” Tanisha said less than a week after being rushed to the emergency room last spring.

“I almost lost her,” said Manuela Daniels, Tanisha’s mom. “She was in the hospital and the medication was not really working for her. Her heart rate raced up. Her oxygen level dropped real low. It was real bad.”

A GENETIC FLAW

Sickle-cell anemia is a genetic disease, one caused by a defective gene passed from parent to child. Tanisha is one of millions of Americans who will develop some kind of genetic illness during their lifetime. No known treatments or cures exist for most of those diseases.

That could soon change now that scientists have decoded the human genome. A visit to the doctor in the year 2010 might be a very different experience from a visit today.

DNA TESTING

By 2010, DNA tests will be a regular part of any medical exam, according to Francis Collins of the National Human Genome Research Institute. Such tests will examine a patient’s genome for defective genes that cause genetic illnesses.

DNA tests will work like early-warning systems. Say your DNA test reveals that you have a gene for heart disease. Your doctor might then advise you to adopt a more healthful diet and a regular exercise program.

Your doctor might also suggest a new drug to help forestall the development of heart disease. Here again, a DNA test would be ordered, this one to help the doctor know how you will react to the drug.

People vary in the ways they respond to medication. For example, some children produce too little of a certain protein that processes a drug used to treat childhood leukemia. (Leukemia is a life-threatening disease marked by an abnormal increase in white cells in the blood.) If a doctor gives the standard dose of that drug to a child without enough protein to process it, the drug can be deadly. A DNA test can now tell doctors which children produce too little of the protein.

In the future, DNA tests could be available for a wide variety of other drugs. The practice of predicting responses to drug therapy from the results of DNA tests is called pharmacogenetics.

GENE THERAPY

After prescribing a drug that best suits your genetic makeup, your doctor might also suggest gene therapy–replacing bad genes with good ones. In the year 2000, gene therapy is a promising, but still experimental, medical tool.

One of the stumbling blocks to effective gene therapy has been developing tough enough vectors. Vectors are vehicles, such as viruses, that can be used to insert healthy genes into human patients. In experimental trials, doctors have injected good genes into viruses, then injected those viruses into human beings. In most cases, the viruses set off the human immune system, which attacked and destroyed the good genes.

In spite of such setbacks, doctors such as Ken McClain are extremely optimistic about the future of genomic medicine. McClain is an associate professor of pediatrics at Baylor College of Medicine in Houston, Texas. One of McClain’s patients is Tanisha Daniels. McClain predicts that new drug therapies for sickle-cell anemia will soon arise. One day, fetuses with sickle cell anemia may be treated with gene therapy inside the womb. Then sickle-cell anemia will vanish. “That’s the dream,” he said.

 

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