Many parents who learn their hearing-impaired child does not carry genetic mutations in either of two genes commonly linked to hearing problems remain confused about the implications of the test results - even after genetic counseling, new research shows.

In contrast, parents who learn their children carry mutations in one of the genes linked to hearing loss appeared to have a better understanding of how the condition is inherited.

Study author Dr. Nina L. Shapiro of the University of California, Los Angeles, explained that many genes can cause hearing loss, but if parents learn their children do not carry the most common mutations, they may not realize the condition could still be genetic.

“A negative result does not mean the hearing loss is not genetic,” she told.

The study findings suggest that people who receive negative results from genetic tests may need to spend extra time with a genetic counselor, to make sure they are not “left without understanding what those results mean,” Shapiro suggested.

However, she emphasized that genetic testing is still important.

During the study, the researchers screened 48 babies with hearing loss for mutations in two genes, called GJB2 and GJB6. None of the infants had a syndrome linked to hearing loss such as Usher syndrome, which also produces dizziness and blindness. Previous research has shown that more than 50 percent of infants who have hearing loss without a particular syndrome have mutations in these genes.

Both genes cue the body to produce a protein called connexin, which allows adjacent cells to communicate with one another in the cochlea, part of the inner ear.

Currently, the American College of Medical Genetics recommends that every newborn with hearing loss be tested for genetic mutations, to determine whether the hearing loss is due to an infant’s genes or environment, and whether it’s part of a syndrome.

The researchers found that 14 out of the 48 babies carried mutations in the GJB2 or GJB6 genes. Parents of the 34 babies who did not carry mutations in either of the genes had more “difficulty grasping the true meaning of the result,” Shapiro said in an interview.

Specifically, parents whose children did not test positive for the mutations were less clear about whether children can inherit hearing loss if it is not present in either parent, or the likelihood of additional children also having hearing loss.

Shapiro explained that the two genes tested for in the study are both recessive, meaning it is possible for both parents to have perfect hearing, but produce a child with hearing problems linked to either gene.

She and her colleagues presented their findings last month at the 20th annual meeting of the American Society of Pediatric Otolaryngology in Las Vegas.