November 14, 2017

Heritability and complex segregation analysis of deafness in Jack Russell Terriers

Patterns between pigmentation and deafness in dogs have been observed for over one hundred years. Scientists therefore have attempted to find some color locus also associated with deafness. In this study, researchers studied the inheritance of deafness in Jack Russell Terriers and observed the sex, coat color, and coat texture influences on the expression of deafness.

Researchers took 176 dogs with normal hearing, 16 dogs that were unilaterally deaf and 9 that were bilaterally deaf (201 total) and studied their pedigree. Deafness was considered from a trichotomous trait view (three categories- normal/bilaterally deaf/unilaterally) and a dichotomous trait view (normal/deaf). In either case, the constructed pedigree suggested genetic inheritance of deafness. The median value for dichotomous deafness heritability was 0.22 and 0.31 for trichotomous deafness. This sufficiently indicates that deafness in the Jack Russell is hereditary, but is not indicative of a single major locus having a large effect, since major loci tend to increase heritability of a trait to greater than 0.7 heritability. Therefore, in the Jack Russell, other loci may be affecting the expression of deafness. Although this study demonstrated heritability, no pattern of inheritance the could be supported by a model of simple autosomal Mendelian locus was observed. Most affected dogs were offspring of two unaffected parents, which eliminates the possibility of a dominant deafness allele. Single recessive inheritance cannot be discarded though because in the pedigree no two bilaterally or two unilaterally deaf dogs were mated. Therefore, further research is needed to determine if a single locus may be influencing deafness.

 When the correlation between color and deafness was studied, dogs that were mostly white were found to be more likely to be deaf than those with a tan color pattern. There was insufficient data to analyze the effects of black coat patterns because only one dog in the pedigree used had black and white coloration. However, the tan verses white comparison supports pigmentation association with deafness. The mean estimate of genetic correlation (the mean of the Gibbs sample) between color and deafness was strong and positive (0.34) for dichotomous deafness with the binary coat color score. However, the precision of this data is lacking so a larger sample of dogs or more quantifiable means of distinguishing coat color will be needed to confidently determine a hearing loss and coloration association.

Famula, Thomas R., Edward J. Cargill, and George M. Strain, 2007. Heritability and complex segregation analysis of deafness in Jack Russell Terriers. BMC Veterinary Research, 3:31.

Original Article: file:///D:/Documents_d/Bio%20of%20Dog%20Breeds/Article%204.pdf

Reviewed by: Katie Snodgrass