- Gonadal dysgenesis results from chromosomal abnormalities in females.
- Cause :
- Genetic abnormality of the chromosome resulting in range of phenotypic abnormalities of the genitalia.
- Most commonly reported chromosome abnormality is 63XO (missing sex chromosome).
- Klinefelter's syndrome (rare) occurs when an extra X chromosome occurs with an XY; the individual is phenotypically male.
- Intersex occurs in XX females with masculinizing gene either mutated or collected from the Y chromosome.
- Signs : infantile reproductive organs and infertility.
- Diagnosis : karyotyping; can be difficult to diagnose phenotypically before puberty.
- Treatment : none available.
- Prognosis : permanent infertility.
- Differentiate from other causes of infertility or abnormal behavior:
- Cryptorchidism .
- Lack of libido .
- Anestrus .
- Aggression .
- Ovarian neoplasia .
- Intersex horses display a range of phenotypes from (almost) complete male to complete female.
- The most common presentation of intersex is a mare with an enlarged clitoris and variously developed abdominal or inguinal testes.
- XXY syndrome results in inhibited testicular development - not evident before puberty.
- Aggressive or male behavior.
- External genitalia normal although vulva may be small. No clitoral enlargement.
- Small for breed (especially 63XO).
- Phenotypic expression in XY sex reversal syndrome is highly variable - feminine to masculine mare.
- Poor conformation .
- XXY mosaics and XY sex reversal may show masculine features.
- Occasional XY sex reversal cases are fertile.
- Other chromosomal abnormalities are phenotypically similar to X monosomy although occasionally they have functional ovaries, ovulate and even conceive.
- Mares with confirmed gonadal dysgenesis, especially 63XO, are usually infertile but occasional cases have been reported as fertile.
- Some mosaic types may be capable of limited breeding.
Reasons for treatment failure
- Most mares with this condition are infertile.