Comparative mapping of the DiGeorge region in the dog and exclusion of linkage to inherited canine conotruncal heart defects.

Conotruncal defects (CTDs) of the heart are a frequent component of DiGeorge, velocardiofacial, or other syndromes caused by deletions of the human chromosome 22q11 region (HSA22q11). In addition, some human patients with isolated nonsyndromic CTDs have been reported to have deletions of this region. Taken together, these findings lead to the conclusion that deletions of an HSA22q11 locus or loci produce abnormalities in cardiac development leading to CTDs. A spontaneous model of isolated inherited conotruncal malformations occurs in the keeshond dog. We have previously shown in experimental matings that nonsyndromic CTDs in the keeshond are inherited in a manner consistent with a major underlying locus. In the studies described in this article we tested two hypotheses: (1) the region of HSA22q11 commonly deleted in DiGeorge and related syndromes is evolutionarily conserved in the dog, and (2) a locus in this region is linked to hereditary CTD in the keeshond. Two loci within the minimal DiGeorge critical region (MDGCR) and two loci that lie telomeric to the MDGCR, one of which is commonly deleted in DiGeorge patients, were mapped in the dog using a combination of linkage analysis and fluorescence in situ hybridization (FISH). The results confirm conserved synteny of the loci DGS-I, CTP, D22S788 (N41), and IGLC on the telomeric end of canine chromosome 26 (CFA26). The group of four syntenic gene loci, which spans a genetic distance of 2.5 cM is the first to be mapped to this small acrocentric canine chromosome and adds gene-associated polymorphic markers to the developing dog linkage map. Linkage of loci in this region to hereditary CTD in the keeshond was excluded.