Doctors have long suspected that genetics must play a role in why some kids get ear infections over and over again, while others do not. But few studies have been able to pinpoint the specific genes involved.

Now, an international team of researchers thinks they've narrowed in on at least one of the genes involved, saying small mutations in a gene called A2ML1 could be at play.

The research was led by Dr. Regie Lyn P. Santos-Cortez, an assistant professor of molecular and human genetics at Baylor College of Medicine who is also trained as an otolaryngologist, or ear, nose, and throat specialist.

She focused on an indigenous community in the Philippines to try to figure out why some were susceptible to ear infections.

Because everyone in the community had a similar socioeconomic status, swam in the same sea water, and ate the same food, the research team knew that the differences between them were more likely to be genetic, rather than environmental.

The team conducted gene sequencing on community members and found that 80 per cent of them who carried the variant in the A2ML1 gene developed middle ear infections, technically called "otitis media."

They also found the same variant in three children from Galveston, Texas, who were also prone to ear infections -- one Hispanic-American and two European-Americans.

Because the variant was found in several ethnic groups, a "founder" effect was likely at play -- meaning a group of people from outside the population brought the gene variant into the two populations several generations ago. In this case, that "founder" would likely have been from Spain.

The gene the team narrowed in on controls the function of a protein that is found in the outermost skin layer, called the epidermis. The research team thinks the protein may play a role in the immune system that protects the ear.

They suspect that those who have a mutation of the gene somehow lose the protection the protein should provide to the ear lining, leading to an ear infection, which is technically called otitis media.

Santos-Cortez's team doesn't think A2ML1 is the only gene involved in predisposing children to middle ear infections, but they suspect it could be an important one. The team now hopes to look further into the mechanism by which A2ML1 variants could cause a susceptibility to ear infections.

The full report on the team's work appears online in the journal Nature Genetics.