Searching for Answers: Celiac and Gluten Sensitivities
Ruling It Out
The genetic test for celiac disease focuses on two particular markers—HLA-DQ2 and HLA-DQ8.
“Ninety-nine percent of celiacs have either HLA-DQ2 or HLA-DQ8,” says Alessio Fasano, MD, medical director at the University of Maryland Center for Celiac Research.
Human leukocyte antigens (HLA) are proteins, of which DQ is a subset, that are found on the surface of almost every cell in the body and are a key component of the immune system. While everyone has slightly different HLA proteins, each of us has two sets, one inherited from each parent.
The snag with the genetic test is that having DQ2 or DQ8 doesn’t mean you have celiac or that you’ll ever develop it. In fact, up to 40 percent of the population has one of these markers and very few of these people will ever get celiac disease.
“There’s no predictive value of developing celiac with DQ2 or DQ8,” explains Fasano. Instead, it’s the absence of the DQ2 or DQ8 marker that’s useful information. Because the chances of developing celiac disease without having either DQ2 or DQ8 are extremely low, Fasano says that “the proper use of the genetic test is to rule out celiac disease.”
There’s little gain in testing someone already diagnosed with celiac, he says. Some celiacs elect to have the test out of curiosity but “for a biopsy-diagnosed celiac, it’s not a value-added test. The genetic information doesn’t change anything about their disease or treatment.”
But there are definite indications for undergoing genetic testing. Three different groups of people can benefit most.
1] Perhaps the largest group is the first-degree relatives of a celiac. These people are at risk of developing the disease, says Fasano, who regularly recommends screening family members with both HLA genetic testing and serological blood tests.
“HLA typing can determine whether doctors should keep an eye on an individual or not,” Fasano explains. “If the individual has a negative test result, the chances of developing celiac are low.”
For Jenna Farley of New York City, it was a relief to discover her newborn son didn’t carry the celiac gene. “I was diagnosed with celiac disease five years ago. When my son was born, I had him tested when he was just a week old,” Farley says. “My two sisters were tested and they both have the DQ2 gene. Now they know to be screened regularly for the disease.”
2] The second group that might consider genetic testing are individuals with medical conditions frequently associated with celiac disease, says Fasano. That includes patients with autoimmune conditions, such as Type 1 diabetes, thyroid disease and Addison’s disease, as well as certain genetic disorders, such as Down’s syndrome.
3] The third group is made up of patients like Abby who are struggling to find a diagnosis and want to know if their symptoms are due to celiac disease or gluten sensitivity.
“This group of patients is not insignificant,” says Fasano, “They may have suffered for years from ataxia [clumsiness symptomatic of a neurologic condition], brain fog or depression without a satisfactory diagnosis. At some point, they may have read about celiac disease and may have given the gluten-free diet a try. In many cases, their symptoms improve on the diet. But because celiac disease requires a 100 percent lifelong commitment to the diet, they want to know where they are on the spectrum of gluten sensitivity. The test can help distinguish if their symptoms are due to celiac disease or gluten sensitivity.”
Perhaps the biggest advantage of the genetic test is that, unlike a blood panel or small intestinal biopsy, being on a gluten-free diet will not alter test results. Gluten-sensitive patients who cannot—or will not—tolerate a gluten challenge (the temporary reintroduction of gluten to the diet) may opt for the genetic test to rule out the disease.
Next: Counting the Cost