Tissue-dependent cellular chimerism characterized by STR and high-resolution aCGH: analysis of two dog cases

Cellular chimerism is a rare genetic condition characterized by the coexistence of two or more genetically distinct cell populations within a single individual. In dogs, this phenomenon is rarely documented but may affect DNA-based identification, parentage verification, and genetic diagnostics in breeding programs. This study aimed to characterize tissue-dependent cellular chimerism in two dogs using short tandem repeat (STR) genotyping combined with array comparative genomic hybridization (aCGH). Two dogs with suspected chimerism identified during routine parentage verification, a Great Dane (Case 1) and a Chow Chow (Case 2), were analyzed using DNA isolated from peripheral blood, buccal epithelium, and hair follicles. STR profiling based on 21 canine microsatellite markers revealed the presence of three or four alleles at multiple loci, with clear variation among tissues. In Case 1, all additional alleles detected across tissues corresponded to parental genotypes, indicating the coexistence of distinct cell lineages. In Case 2, a more complex pattern was observed, with extensive tissue-specific variation and up to four alleles detected at individual loci. Genome-wide aCGH analysis revealed numerous copy number alterations, most frequently detected in buccal epithelium. In the Great Dane, differences in X chromosome copy number between tissues were consistent with the coexistence of XX and XY cell lines. Our findings demonstrate that chimerism in dogs may exhibit pronounced tissue-specific distribution and remain undetected by routine genetic analyses based on a single biological sample, underscoring its potential impact on DNA-based testing used in canine breeding and genetic diagnostics.