Trisomy-X

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Photomicrograph of the cortex and superficial medulla of an ovary from a trisomy-X bitch, showing subepithelial structures and prominent cross sections of immature sex cords[1]

Trisomy-X (Chromosomal aneuploidy; super females) is a genetic disease characterized by XXX sex chromosome rather than the normal XX[2].

Aneuploidy is the result of non-disjunction during meiosis and can be associated with clinical signs in the offspring, depending on the chromosomes that are either absent or in excess[3].

Several cases of aneuploidy have been reported in dogs, and cytogenetic investigations of intersex dogs have revealed cases of XXY trisomy and X monosomy[4], but only a few cases of X trisomy are described in dogs[5].

Most cases present with either primary anestrus or infertility, despite the occurrence of estrous cycles[6][7].

Clinically affected bitches are usually infertile but physically normal with unambiguous female genitalia, though often shy or timid[8].

Primary clinical symptoms include a history of estrous cycle abnormalities included persistent anestrus, anovulation, a slow rise in serum progesterone and testosterone concentrations, 'split' heats, insufficient luteal phase and persistent estrus[9], ovarian cysts, ovarian tumor, endometrial hyperplasia, mucometra, hydrometra, and uterine infection.

Affected bitches also have a higher risk of dental abnormalities such as oligodontia.

Ultrasonography may reval abnormalities within the ovarian or uterine structure but definitive diagnosis requires chromosomal testing.

Histological examination of ovaries during ovariohysterectomy may reveal hypoplastic ovarian tissue with poorly differentiated sex cords and little evidence of primordial or mature follicles.

However, based on incidence studies, it is suspected that the majority of canine trisomy-X cases may escape diagnosis, because accompanying symptoms of reproductive disturbance, skeletal malformations, and behavioral or psychiatric disorders can be so mild that karyotyping is not performed[10].

Ovariohysterectomy is usually advised in order to limit transmission of the condition vertically to offspring. However, some dogs may be required to be treated and a GnRH agonist, gonadorelin can be given at a dose of 2.2 μg/kg intramuscularly, once daily for 3 days to induce progression in the cycle[11].

References

  1. O'Connor CL et al (2011) Trisomy-X with estrous cycle anomalies in two female dogs. Theriogenology 76(2):374-380
  2. Raudsepp T et al (2012) The pseudoautosomal region and sex chromosome aneuploidies in domestic species. Sex Dev 6(1-3):72-83
  3. Hall H et al (2006) Meiosis and sex chromosome aneuploidy: how meotic errors cause aneuploidy; how aneuploidy causes meiotic errors. Curr Opin Genet Dev 16:323–329
  4. Meyers-Wallen, VN (1993) Genetic of sexual differentiation and anomalies in dogs and cats. J Reprod Fertil 47:441-452
  5. Johnston, SD et al (1985) X trisomy in a airedale bitch with ovarian dysplasia and primary anestrus. Theriogenology 24:597-60
  6. Goldschmidt B et al (2003) Infertility related to X-trisomy in a Labrador retriever bitch. J Israeli Vet Med Assoc 58:1
  7. Johnston SD et al (1985) X trisomy in an Airedale bitch with ovarian dysplasia and primary anestrus. Theriogenology 24:597–607
  8. Switonski M et al (2000) X trisomy in an infertile bitch: cytogenetic, anatomic, and histologic studies. J Hered 91:149–150
  9. Meyers-Wallen VN (2007) Unusual and abnormal canine estrous cycles. Theriogenology 9:1205–1210
  10. Concannon P (2009) Endocrinologic control of normal canine ovarian function. Reprod Domest Anim 44:3–15
  11. Kutzler MA (2007) Estrus Induction and synchronization in canids and felids. Theriogenology 68:354–374