March 15, 2010

Gene Linked to Food Allergy-Related Disorder

Photo of a family cooking

Scientists have linked a region of a human chromosome with eosinophilic esophagitis (EoE), a recently recognized disorder that can cause difficulty eating and is associated with allergies to certain foods. They've also identified a gene that’s likely involved in the disorder.

EoE is characterized by inflammation and accumulation of a specific type of immune cell, called an eosinophil, in the esophagus. Symptoms of EoE vary with age. In young children, a major symptom is spitting up food. In older children and adults, the inflammation and swelling can cause food to become stuck in the esophagus. Symptoms may improve with a special liquid formula diet or a diet that lacks 6 highly allergenic foods: milk, soy, eggs, wheat, peanut and seafood.

EoE differs from more common food allergies, which can have serious consequences as well. Little is known about what causes EoE, but the disease runs in families, suggesting that specific genes may be involved.

To find genes associated with EoE, a team of researchers led by Dr. Marc Rothenberg at the Cincinnati Children’s Medical Center Hospital and Dr. Hakon Hakonarson at the Children's Hospital of Philadelphia performed a genome-wide association analysis. They searched across the entire human genome for genetic variations between children with EoE and healthy children. The work was supported by NIH’s National Institute of Allergy and Infectious Diseases (NIAID) and National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) as well as other sources.

In the March 7, 2010, edition of Nature Genetics, the researchers reported that changes in genes within a region on chromosome 5 were highly associated with EoE. One of the genes in this region encodes a protein called thymic stromal lymphopoietin (TSLP). TSLP is made by epithelial cells, which line internal and external surfaces of the body. The protein is already thought to be involved in other allergic diseases, such as asthma and atopic dermatitis (eczema).

When the investigators measured expression levels of TSLP, they found that it was expressed at significantly higher levels in children in children with EoE than in those without the disorder. "We haven’t totally confirmed it, but it appears 99% likely that this is the culprit," Hakonarson says.

The researchers are now sequencing the gene in people with and without EoE, aiming to link specific mutations with disease. Using mice and cell cultures, they are also investigating the mechanism by which elevated TSLP might lead to EoE.

This finding could one day lead to a genetic test for TSLP that would help doctors identify patients who need special diets. Strategies to block the production or function of TSLP might prove useful in treating EoE as well as other allergic diseases in the future.

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