Felis ISSN 2398-2950

Disorders of sexual development

Synonym(s): Inter-sex, hermaphrodite, pseudohermaphrodite, sex-reversal, mosaic, chimera

Contributor(s): Gradil Carlos, Sophie Grundy, Autumn P Davidson


  • Abnormalities of sexual development and differentiation are complicated. Abnormalities of sexual development may involve one or more errors of chromosomal sex, gonadal sex, or phenotypic sex. Prior to considering the different inter-sex abnormalities it is vital that the definition of chromosomal, gonadal and phenotypic sex, is understood.
  • It is important to appreciate that normal sexual development requires interplay between the sex chromosomes (chromosomal sex), genes encoding for sexual differentiation (gonadal sex), subsequent hormone production and reproductive tract development (phenotypic sex). Abnormalities may occur anywhere along this chain of events resulting in atypical individuals. Individuals affected by abnormalities of sexual differentiation are therefore best described in terms of their chromosomal, gonadal and phenotypic sex.
  • Chromosomal Sex: Chromosomal sex defines or classifies an animal by the type of sex chromosomes that they have. Normal dogs and cats have two sex chromosomes; one sex chromosome should be received from each parent. A chromosomal female has two equivalent sex chromosomes (XX) and a chromosomal male has two differing sex chromosomes (XY). Chromosomal sex may also be referred to as karyotypic or genetic sex.
  • Gonadal Sex: Gonadal sex defines or classifies an animal by the type of gonads that they develop. Gonadal females have ovarian tissue, gonadal males have testicular tissue. Animals with a mixture of gonadal types, either an ovary and a testis, or an ovotestis are referred to as true hermaphrodites.
  • Phenotypic Sex: Phenotypic sex refers to the internal and external genitalia being female, male, or a combination of both.



  • Abnormalities of Chromosomal Sex: Chromosomal abnormalities may result from abnormal cell division or fusion. Trisomy refers to the presence of three sex chromosomes, monosomy one sex chromosome. The phenotypic sex of these individuals is generally male (XXY) or female (XXX or XO).
    • Mosaicismrefers to individuals with cell populations of different chromosomal constitution.
    • Chimerismrefers to an individual composed of two different cell populations derived from different zygotes. In mosaics and chimeras the type of gonadal sex that develops will vary with the proportion of XX and XY cells. Phenotypic sex will depend upon the subsequent function of the gonads present.
  • Abnormalities of Gonadal Sex: The genes responsible for gonadal sex development are still under investigation however; the presence or absence of the sex determining region (Sry) of the Y chromosome; and Dax-1 on the X chromosome are known to be important for gonadal sex development.
    • Animals with gonads that do not match their chromosomal sex are referred to assex-reversed.
    • XX hermaphrodites have both testicular and ovarian tissue.
    • XX males have testicular tissue only.   
  • Abnormalities of Phenotypic Sex: The development of the phenotypic sex (internal reproductive tract, accessory sex glands and external genitalia) is dependant upon the presence or absence of testicular tissue.
    • In the absence of testes the internal reproductive tract and external genitalia will develop as a female from the mullerian ducts.
    • If testes are present, testosterone and mullerian inhibiting substance (MIS) are released. Under the influence of MIS and testosterone the internal reproductive tract, and external genitalia will develop as a male from the wolffian ducts, and the 'female' mullerian ducts will regress.
    • Pseudohermaphrodites have chromosomal and gonadal sex that agrees, but ambiguous internal or external genitalia.
    • Female pseudohermaphrodites are XX, with bilateral ovaries and masculinized androgen responsive organs.
    • Male pseudohermaphrodites are XY with bilateral testes yet have some degree of female internal or external genitalia. These animals result either from a failure of Mullerian duct regression or failure of androgen-dependent masculinization.


  • Female pseudohermaphroditism may result from in utero exposure to exogenous androgens or progestagens during the time of internal and external genitalia development (typically 34-46 days post LH surge).


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Amo An, De Luca J & Zufriategui L et al (2001) Male pseudohermaphroditism in a dog: a case report. Com Therio (1), 1-11 ResearchGate.

Other sources of information

  • Meyers-Wallen, VN (2001) Inherited Abnormalities of Sexual Development in Dogs and CatsRecent Advances in Small Animal Reproduction, IVIS (www.ivis.org), New York, USA.