All it takes is a brush, an envelope and a postage stamp to find out if you have America's most common genetic disorder. 

The brush, which picks up loose cheek cells and the DNA inside them, is part of a mail-in genetic testing kit for hereditary hemochromatosis. 

One in nine Americans carries a gene for this disorder, which makes the body unable to get rid of excess iron. About 1 in 300 develops a full-blown form of it. It is more common among people of Scottish and Irish descent than among the general population. 

Symptoms of hemochromatosis include chronic fatigue, impotence or amenorrhea, diabetes, liver failure, heart disease and early death, according to the Centers for Disease Control and Prevention. 

"Hemochromatosis is an epidemic in this country," said Sandra Thomas, founder of the American Hemochromatosis Society, "yet most people don't know they have it." 

The good news about hemochromatosis is that a simple treatment — regular blood donation — can effectively treat it when it is diagnosed in the early stages. Removing red blood cells removes excess iron from the blood and prevents buildup in the organs. 

Why Get Tested? 

The most compelling reason to get tested for hemochromatosis is knowing a family member has the disorder. But even if nobody in your family has been diagnosed, this doesn't mean you're in the clear. Your ancestors might have been misdiagnosed with something else, since the common symptoms of hemochromatosis can easily masquerade as other ailments. 

Take Karyn Arkell of Kelowna, British Columbia, who was initially diagnosed with lupus when she began to develop chronic fatigue and depression in her 20s. Arkell's paternal grandmother had apparently died of lupus, so it seemed like the most logical explanation for her symptoms, she wrote in an e-mail to FOXNews.com. 

A few years ago, Arkell read an article about hereditary hemochromatosis and asked her doctor to test the iron levels in her blood. Her iron levels were abnormally high, but her doctor still wasn't convinced that she had hemochromatosis. She insisted on a genetic test. 

"One month later, the test came back and stated I indeed had hemochromatosis," Arkell said. After beginning regular blood donation a year ago, Arkell has begun to experience a vitality she hasn't felt since her teens. "For about the last 5 months I have been feeling on top of the world," she wrote. "I just ran 5 km last night." 

Mail-In Medicine 

The ordinary first step in hemochromatosis testing is to go to your doctor and request a blood test for serum iron, TIBC (total iron binding capacity), percent of saturation and serum ferritin — all measures that would pick up an excess of iron in the blood, according to the Hemochromatosis Foundation. 

If iron levels are high, or you have some other reason to believe you might have the disorder, you can take a genetic test. Some labs and hospitals offer the test on an outpatient basis, but Denver-based Kimball Genetics manufactures a mail-in test that costs around $125. 

The test consists of two cheek brushes in sterile packets, an instruction book and fact sheet about hemochromatosis, as well as a padded envelope to send back the samples. 

The instructions are quite straightforward: with two small wire brushes, you rub 20 times along the inside lining of the cheek. The brush is supposed to pick up free cheek cells. After letting the "sample" dry on the brush, you wrap it in the package and send it off to the lab. 

The lab requires you to provide the name and fax number of a physician who can officially receive your results, which are generally available within two business days. 

Getting Results 

The results tell you specifically that the lab ran a test for the two mutations that lead to hemochromatosis. But a negative result does not completely eliminate the possibility that you will develop the disease. 

"Some hemochromatosis cases — less than 5 percent of cases in Caucasians — are caused by genetic defects that are so far unknown," according to Kimball Genetics. 

In other words, the major genes for hemochromatosis have been discovered. But given that scientists have just lined up the raw sequence of our master code and have not yet figured out what all of these parts of the sequence mean, there may be rarer flaws that can lead to hemochromatosis in a few cases. 

So why get tested at all if it's not 100 percent definitive? 

One reason is that a positive result can lead to early preventative treatment. 

Since Arkell insisted on being tested, her daughter has been tested too. "My daughter has it, but luckily she shouldn't suffer like me," Arkell said. "That to me is the most important thing on earth."