Texas A&M researchers conduct study to identify canine deafness genes

COLLEGE STATION, TEXAS — Identifying the cause of hereditary deafness in dogs to prevent deaf offspring is a goal of ongoing research being conducted at Texas A&M's College of Veterinary Medicine.

In an effort to create breed specifications, dogs that carry genetic disorders have been bred continually, propelling the problem in future generations.

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Dalmatian and English Setters are two breeds studied by Dr. Keith Murphy, a geneticist in the university's veterinary pathobiology department.

The research, which began in 1999, focuses on identifying the genes that cause diseases. Once that work is accomplished, the research agenda swings to eliminating the genes from the gene pool, or finding ways to treat the defect.

Roughly 30 percent of all Dalmatians and 14 percent of English Setters in the United States are born deaf in at least one ear, Murphy says.

The goal is to identify the gene or genes that permit the abnormality to occur at such a vast rate.

Additional information was collected on the breeds nationally to include individual pedigree details. Murphy says he plans to conduct hearing tests to pinpoint the genes involved in causing deafness.

The team of researchers found that deafness in Dalmatian and English Setters does not follow a specific pattern of inheritance, so the entire canine genome is being studied.

Many scientists agree that there is a correlation between animals' pigment and their predisposition to deafness, Murphy says.

Goals of the study were to estimate the heritability of deafness in U.S. breeds and through segregation analysis, determine if there is a segregating locus that has a large effect on deafness.

The brainstem auditory-evoked response method was used to diagnose 199 out of 266 Dalmatians' deafness. Of that sum, 148 (74.4 percent) dogs had normal hearing, while 36 (18.1 percent) were unilaterally deaf and 15 (7.5 percent) were bilaterally deaf, according to study findings.

"A heritability of 0.73 was estimated considering deafness a dichotomous trait, and 0.75 was estimated considering deafness a trichotomous trait," Murphy says. "Although deafness in the Dalmatian is heritable, the evidence for the presence of a single major gene affecting the disorder is not."

Human diseases often are identical to canine diseases. By studying human disease, answers can be found for canines, too, Murphy adds.