A Rare Case of Testicular Disorder of Sex Development in a Dog (78,XX; SRY-Negative) with Male External Genitalia and Detection of Copy Number Variation in the Region Upstream of the SOX9 Gene

Testicular or ovotesticular disorder of sex development (DSD) in genetic females (78,XX; SRY-negative) has been reported quite frequently in numerous dog breeds and is usually diagnosed due to the presence of female external genitalia with an enlarged clitoris. The molecular background of this disorder, diagnosed also in human and other mammals, is not fully understood. However, it has recently been proposed that a copy number variation (CNV) in the region upstream of the SOX9 gene is associated with it. We described a rare case of this disorder in a French Bulldog with abdominal testes and male external genitalia (a slightly malformed penis). FISH studies showed a female karyotype, lack of a translocation involving the Y chromosome, and a distinct size variation in the CNV region (CNVR) upstream of the SOX9 gene, located on chromosome 9 (CFA9). A large FISH variant on a single CFA9 and a lack of the variant on its homologue was observed. Surprisingly, in the mother of this DSD dog, 2 normal-sized variants were identified which means that the CNV in the DSD dog was de novo. Our observations are in agreement with earlier suggestions that a high number of copies at the CNVR upstream of SOX9 may be associated with this type of DSD.