Copy number variation of the SRY gene showed an association with disorders of sex development in Yorkshire Terrier dogs

The molecular background of disorders of sex development (DSD) in dogs is poorly understood. Several copies of the SRY genes have been reported in the dog genome. We used droplet digital PCR with the aim of determining variability in SRY copy number and its association with DSD in dogs. Altogether 19 DSD male dogs (XY DSD) of 10 breeds and 87 control dogs of eight breeds were analyzed. Moreover, we performed a comparative analysis of SRY copy number in other canids: wolves (3), red foxes (16), and Chinese raccoon dogs (10). We found that the modal number of SRY copies in dogs, wolves, red foxes, and Chinese raccoon dogs was 3, 3, 1, and 3 respectively. Variability of copy number was only observed in Yorkshire Terriers (two or three copies) and red foxes (one or two copies). An analysis of six DSD Yorkshire Terriers and 38 control males of this breed showed that 50% of the DSD dogs had two copies, while the incidence of this variant was significantly lower in the control dogs (10.5%). Searching for the copy number of the coding and 5'-flanking fragments revealed full concordance with the copy number. These fragments were also sequenced in DSD (19) and control (24) dogs, and no DNA variants were found. We conclude that, in the dog, two or three functional copies of the SRY gene are present, and a smaller number of copies showed an association with the risk of DSD phenotype in Yorkshire Terriers.