A threshold model analysis of deafness in Dalmatians.

To elucidate the inheritance of deafness in Dalmatian dogs, 825 dogs in 111 litters were evaluated for abnormalities in hearing through the brainstem auditory evoked response (BAER). Recorded along with their quality of hearing (normal, unilaterally deaf, or bilaterally deaf) were the sex, coat color, eye color and the presence or absence of a color patch. The analysis considered deafness an ordered categorical trait in a threshold model. The underlying, unobservable continuous variate of the threshold model was assumed to be a linear function of sex of dog, coat color (black or liver and white), color patch (presence or absence), eye color, the deafness phenotype of the parents and a random family effect. Twenty-six percent of dogs were deaf in at least one ear. Eye color, color patch, sex and the hearing status of the parents were all significant contributions to deafness. The heritability of deafness, on the continuous unobservable scale, was 0.21. This value was computed after correction for eye color, color patch, parental hearing status and sex, implying that significant genetic variation exists beyond the contribution of several single loci.