Robertsonian translocation in a sex reversal dog (XX, SRY negative) may indicate that the causative mutation for this intersexuality syndrome resides on canine chromosome 23 (CFA23).

A Bernese mountain dog was subjected for clinical evaluation due to the presence of ambiguous external genitalia (enlarged clitoris). Anatomical and histological studies revealed the presence of one testicle, one ovotestis and a uterus. This dog was classified as a female-to-male sex reversal, with 2 normal X chromosomes and a lack of the Y chromosome-linked genes SRY and ZFY. It is the first case of this syndrome in this breed. Apparently a Robertsonian translocation, rob(5;23), was also identified in this dog and it is again the first case of this type of chromosome abnormality in this breed, as well as the first case of co-occurrence of the sex reversal syndrome along with a centric fusion in the dog. Since on the canine chromosome 23 (CFA23) 3 genes (FOXL2,PISRT1 and CTNNB1) involved in the sex determination process are present, further cytogenetic FISH studies were carried out with the use of BAC probes specific for this chromosome. It was found that a pericentromeric fragment of CFA23 was deleted as a result of the centric fusion. We hypothesize that a cis regulatory sequence for the sex determination genes on CFA23 (e.g. proximally located CTNNB1) is present in the deleted fragment. Thus, a causative mutation responsible for this sex reversal syndrome may reside on CFA23.