Abstract
One of the most unique coat color patterns in the domestic dog is merle (also known as dapple in the dachshund breed), characterized by patches of normal pigmentation surrounded by diluted eumelanin pigment. In dogs, this striking variegated pattern is caused by an insertion of a SINE element into the PMEL gene. Differences in the length of the SINE insertion [due to a variable-length poly(A)-tail] has been associated with variation in the merle coat color and patterning. We previously performed a systematic evaluation of merle in 175 Australian shepherds and related breeds and correlated the length of the merle insertion variants with four broad phenotypic clusters designated as “cryptic”, “atypical”, “classic”, and “harlequin” merle. In this study, we evaluated the SINE insertions in 140 dachshunds and identified the same major merle phenotypic clusters with only slight variation between breeds. Specifically, we identified numerous cases of true “hidden” merle in dachshunds with light/red (pheomelanin) coats with little to no black/brown pigment (eumelanin) and thus minimal or no observable merle phenotype. In addition, we identified somatic and gonadal mosaicism, with one dog having a large insertion in the harlequin size range of M281 that had no merle phenotype and unintentionally produced a double merle puppy with anophthalmia. The frequent identification of cryptic, hidden, and mosaic merle variants, which can be undetectable by phenotypic inspection, should be of particular concern to breeders and illustrates the critical need for genetic testing for merle prior to breeding to avoid producing dogs with serious health problems.
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Acknowledgements
The authors express their appreciation to all of the dogs and their owners who participated in this study, and special thanks to Rob Westra and Daniela Flores for their critical reading of the manscript and helpful discussions.
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Funding for this study was provided by Genetic Veterinary Sciences, Inc.
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LGS, BCB, and LJE contributed to the study conceptualization and design. Sample recruitment, photo collection, and pedigree chart construction were performed by LJE for the large six-generation pedigree. PMEL testing, laboratory supervision, and results analysis was performed by HFS, CJR, CRC, KS, and BCB. BCB performed the final analysis of the combined dataset and wrote the first draft of the manuscript. All authors commented on and approved the final manuscript.
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LGS is the owner of Genetic Veterinary Sciences, Inc., DBA Paw Print Genetics which provides genetic testing on a fee-for-service basis. The remaining authors have no conflicts of interest to declare.
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Informed consent was obtained from the owners of dogs specifically recruited for this study. The remaining samples were anonymized from samples that would have been otherwise discarded following routine diagnostic testing.
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All canine samples included in this study were obtained through consent of the individual owners or were obtained from otherwise-discarded DNA samples after clinical testing at Paw Print Genetics.
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All photographs included in this study were used with permission from the dog owners.
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Ballif, B.C., Emerson, L.J., Ramirez, C.J. et al. The PMEL gene and merle (dapple) in the dachshund: cryptic, hidden, and mosaic variants demonstrate the need for genetic testing prior to breeding. Hum Genet 140, 1581–1591 (2021). https://doi.org/10.1007/s00439-021-02330-y
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DOI: https://doi.org/10.1007/s00439-021-02330-y