November 18, 2018

Sry-Negative XX Sex Reversal in the German Shorthaired Pointer Dog

 

In 1995, a group of researches wanted to find the causes of XX Sex Reversal in German Shorthaired Pointer Dogs. XX Sex reversal is when the sex determined by the dog’s chromosomes is female (XX) but the dog develops testicular tissue or a penis. The issue had recently been discovered in several German Shorthaired Pointers prompting this investigation into the causes and frequency of this genetic disorder (370). Known causes of XX sex reversal are Y to X translocations during metaphase of male meiosis and mutations of the Sry gene (370). Additionally, researches were able to use previous knowledge of this affliction as this issue had previously been explored in Cocker Spaniels (370). In the previous study, it was discovered that a mutant autosomal gene was responsible for the XX Sex reversal in the Cocker Spaniels so the team decided to use genetic and pedigree analysis to find the source of this likely genetic illness (370).

Mayers-Wallen et al. collected affected pointer dogs with the presence of “(1) unilateral or bilateral ovotestes in gonadal histology, or (2) an enlarged clitoris containing a bone, associated with an otherwise normal female external phenotype” and compared them to a group of non-XX-sex-reversed Labrador Retrievers as a control group. DNA was extracted from both groups and pedigree analysis was performed on the pointer dogs (370). In the genetic analysis, researches looked for mutations in the Canine HPRT gene and the Sry HMG Box (370). The HPRT is a housekeeping gene that is conserved throughout many animals and a defect in this gene would lead to more genetic mutations and possibly this illness, the Sry HMG Box is a similar gene that codes more specifically for housekeeping the Sry region of the genome so mutations in this region would also result in more genetic mutations. Results of the test showed that the HPRT gene was present but “the Sry HMG box is absent in genomic DNA of sex reversed [German Shorthaired Pointers]” (372). Meanwhile, the pedigree analysis showed that twelve of the dogs with this condition were from the same family and all related back to one male ancestor (371). This data suggests that:

Since the HMG box is thought to be essential to the action of the Sry gene product in inducing testicular differentiation, these results indicate that neither a Y to X translocation nor a mutation of the Sry gene is likely to be responsible for testis induction in this model. (372)

Instead, researchers believe that “a mutation in an autosomal gene in the testis differentiation pathway” is a better fit to explain the XX Sex reversal (372). Unfortunately, researches were unable to explain which gene is responsible but were able to determine that it is a family illness and therefore unlike to affect the breed as a whole (372-373).

 

Reference: https://academic.oup.com/jhered/article-pdf/86/5/369/6452127/86-5-369.pdf

 

V. N. Meyers-Wallen, L. Bowman, G. M. Acland, V. L. Palmer, D. Schlafer, V. Fajt; “Sry-Negative XX Sex Reversal in the German Shorthaired Pointer Dog”, Journal of Heredity, Volume 86, Issue 5, 1 September 1995, Pages 369–374, https://doi.org/10.1093/oxfordjournals.jhered.a111605

 

Reviewed by Ian J. Sessions | 17 November 2018