Scientists explore celiac disease genes and frequency of celiac disease testing in Black people
By Amy Ratner, director of scientific affairs.
Two separate studies related to race and potential healthcare disparities in celiac disease were presented recently as posters at Digestive Disease Week (DDW).
Researchers at the University of Alabama investigated the frequency with which the genes associated with celiac disease were found in Black people.
And investigators at the Cleveland Clinic looked at differences in the frequency of blood testing for celiac disease in those who had a biopsy that showed intestinal damage. They were seeking to determine whether Black people were tested for celiac disease at the same rate as white people.
Black people are at genetic risk for celiac disease, the University of Alabama researchers concluded.
“Genetic risk and prevalence of celiac disease in Black people is largely unknown and thought to be rare,” the study says, leading researchers to launch their investigation.
Researchers reviewed records of adults who had haplotyping tests done at the University of Alabama HLA laboratory primarily to be considered as organ donors or recipients. The study included about 11, 500 Black people and about 14,000 white people. The University of Alabama HLA lab, the only accredited HLA lab in the state, maintains a registry of all HLA typing performed, as well as patients’ demographics, the authors wrote. University of Alabama has a diverse patient referral base, the study notes. Haplotyping can identify patterns of genetic variation that are associated with health and disease.
Black people had similar frequency of having HLA DQ2 alleles, but less frequent HLA DQ8 alleles than whites, the study found. Alleles are one of two or more versions of a genetic sequence at a particular region on a chromosome. An individual inherits two alleles for each gene, one from each parent.
HLA DQ2 and HLA DQ8 are the genes found in almost everyone who has celiac disease, with only one copy of one of the genes needed to develop the condition. But genes alone are not enough. In fact, the genes associated with celiac disease are found in 30 to 40 percent of the general population, but only 1 percent of the general population has celiac disease. Environmental factors are also involved in the development of celiac disease, though the exact cause has not yet been determined. Gluten from wheat, barley or rye also must be consumed for someone with the associated genes to develop celiac disease.
About 5,500 Black people and about 6,500 white people had the genes associated with celiac disease, the study found.
Among those with the genes, about 35 percent of Black people and 33 percent of white people had one copy of the DQ2 gene, while about 3 percent in each group had two copies of the DQ2 gene.
About 2 percent of Black people and 7 percent of white people had one copy of both DQ2 gene and DQ8 gene.
While these percentages reflect how common the genes were in both study groups, they may not reflect how common they are in the general population because study participants were all being evaluated to be transplant organ donors or recipients, said Amanda Cartee, MD, a gastroenterologist at the University of Alabama and one of the study authors. Cartee presented earlier data at DDW in 2022 that showed Black people are much less likely than white people to have gene tests for celiac disease.
About 16 percent of white people in the new study had one copy of the DQ8 gene, compared to about 6 percent of Black people. Two copies of the DQ8 gene were found in 0.6 percent of white people and about 0.08 percent of Black people.
The study also found that about 50 percent of Black participants and about 40 percent of white participants had haplotypes other than DQ2 or DQ8 and would be highly unlikely to develop celiac disease. Cartee noted there is some emerging data on another gene that might be related to celiac disease, but that was not evaluated in this research.
Study limitations include the fact that the study population was largely composed of those undergoing transplant evaluation. Additionally, there are disparities in evaluation for transplants and transplantation, the authors note.
The study was limited to an investigation of who had the genes associated with celiac disease and was not designed to determine who went on to to develop celiac disease. Additional studies that assess the frequency of genes related to celiac disease in diverse populations and investigate the progression to celiac disease in those who have the genes are important to understanding the role of genetic risk in non-white populations, the study authors note.
Cleveland Clinic researchers reviewed 10 years of health records of adults who had biopsies that showed intestinal damage to determine if they had subsequent blood tests for celiac disease. Their study included about 1,700 patients. Of these, about 130 were Black.
“Recent work has shown an increased prevalence of celiac disease among numerous racial and ethnic groups, but diagnosis is affected by the frequency of testing.” the authors wrote. “We sought to assess health disparity in celiac disease.”
Overall, about 73 percent of white patients, about 1200, had celiac disease blood tests done, compared to about 55 percent of Black patients, about 70. A significant difference in testing frequency was found when researchers analyzed results based on race alone.
But when they considered other factors, including gender and age, being a man was the only factor significantly associated with having been tested for celiac disease less frequently. “The frequency of testing was lower among [Black] patients, but not after correcting for age and gender,” the study says.
Meanwhile, older study participants were tested more frequently.
Among white people who were tested for celiac disease, the test was positive in about 43 percent compared to about 15 percent in Black people. Blood tests for celiac disease included anti-tissue transglutaminase (TTG) IgG or IgA, anti-endomysial (EMA), or anti-deamidated gliadin peptide (DGP) antibodies. Researchers concluded that advocacy for increased testing in men and Black patients with intestinal damage is needed.
An earlier study, the one presented by Cartee in DDW in 2022, found that Black people with biopsy confirmed celiac disease were more likely than non-Hispanic whites to have had negative results on the TTG test, raising questions about its accuracy in diagnosing celiac disease in Black patients.
DDW is the largest international gathering of physicians, researchers and academics in the fields of gastroenterology, hepatology, endoscopy and gastrointestinal surgery. Studies presented at DDW as posters are often preliminary and give an early look at investigations that are likely to include more details as they progress toward publication in a peer reviewed journal. Posters selected to be presented at DDW go through a review process