Lack of the SOX9 Gene Polymorphism in Sex Reversal Dogs (78,XX; SRY negative)

The molecular background of the most frequent intersexuality syndrome in dogs (female-to-male sex reversal with the female karyotype and a lack of the SRY gene) is unknown. In this article, new cases of this syndrome are described in two unrelated American Staffordshire terrier dogs and one miniature pinscher dog subjected to cytogenetic and molecular analysis due to the presence of an enlarged clitoris. One dog was operated on and histological studies of the gonads revealed a testicular structure without signs of spermatogenesis, but the uterus wall appeared to be normal. All three dogs had female chromosome complements and lacked the Y-linked genes SRY and ZFY. Eight fragments, representing the vast majority of the coding sequence of the SOX9 gene, and two fragments of the 5' flanking region of this gene were analyzed. The studied fragments had identical DNA sequences when comparing the intersexual dogs with GenBank sequences (AY237827; NW139883). Thus a mutation in the coding sequence as well as the promoter region of the SOX9 gene might be excluded as a cause of this type of intersexuality. The importance of further studies of the 5' flanking region of this gene is discussed.