Development of a multiplexing strategy for whole genome scans of the domestic dog and analysis of hereditary deafness in the Dalmatian

The Dalmatian is affected by deafness more than any other breed of domestic dog, with 30% of the United States population suffering from unilateral or bilateral deafness. The genetic origin of deafness in the Dalmatian is unknown. The objective of this work was to identify, using linkage analysis, any chromosomal region(s) in which the gene(s) responsible for deafness in the Dalmatian may be located. To achieve this objective it was necessary to 1) develop multiplexed microsatellite markers for an efficient whole genome scan, 2) assemble a multigenerational Dalmatian kindred segregating deafness, 3) estimate the heritability of deafness and perform complex segregation analysis, and 4) perform linkage analysis of deafness, and other phenotypic traits, in the Dalmatian kindred. A set of 172 microsatellite markers, termed Minimal Screening Set 1 (MSS1), was characterized, prior to this work, for whole genome scans of the domestic dog. 155 of the MSS1 markers were multiplexed into 48 multiplex sets. Amplification of the multiplex sets was achieved using a single thermal cycling program. The markers were labeled with fluorescent dyes and optimized for resolution on an ABI 310 Genetic Analyzer or ABI 377 Sequencer. A kindred of 266 Dalmatians was assembled, of which 199 had been diagnosed using the brainstem auditory evoked response to determine auditory status. Of these, 74.4% (N = 148) had normal hearing, 18.1% (N = 36) were unilaterally deaf, and 7.5% (N = 15) were bilaterally deaf. A heritability of 0.73 was estimated considering deafness a dichotomous trait and 0.75 as a trichotomous trait. Although deafness in the Dalmatian is clearly heritable, the evidence for the presence of a major gene affecting the disorder was not persuasive. Dalmatians (N = 117) from the assembled kindred were genotyped for the MSS1 markers (149 were polymorphic). Linkage analysis was performed for deafness, eye color, and spot color. The maximum LOD scores for deafness were found with markers Cos15 on CFA17 (LOD = 1.69) and FH2585 on CFA28 (LOD = 1.34). No significant linkage was found with eye color. Significant linkage for spot color was found with marker FH2319 (LOD = 9.7) on CFA11.