Genetic Inheritance and its Environment

Cryptorchidism - Undescended Testes


Unilateral or bilateral retention of the testicle(s) from descending into the scrotum

  • Usually congenital, rarely acquired
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  • Sterility with bilateral cryptorchids
  • Inheritance of genetic components with unilateral cryptorchids
  • Undesirable masculine behavior after castration i.e. stallion behavior, aggression. (Mueller 1999)
  • Germ cell deterioration due to high temperatures results in general testicular malignancies (Romagnioli 1991)
Cryptorchidism is more common in companion animals, pigs, or humans (2-12%) than in cattle or sheep (<1%). Laboratory animals are rarely cryptorchid (Amann and Veeramachaneni 2007).

Animals at Risk


American Quarterhorses, Saddlebreds, Percherons, and pony breeds (Hayes 1986).


German Shepard, Chihuahua, Yorkshire Terrier, Staffordshire Terrier, Shih Tzu, and Miniature Poodle (Yates and Hayes 2003)


Dutch, Lithuanian, British and Italian (Virtanen and Toppari 2007).

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Described by location of undescended testicle(s).
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  • Can be autosomal dominant or autosomal recessive depending on the targeted gene
  • Sex linked: only occurs with male chromosomes
  • Polygenic trait: many contributing genes affect the multiple stages of testicular descent
  • Environmental affects in utero and post natal seen with spontaneous descent.

Targeted Genes

Each protein affects different stages of testicular descent

INSL3: insulin-like factor 3. Enlarges gubernaculum for initial testicle descent (Amann and Veeramachaneni 2007).

LGR8: leucine-rich repeat containing G protein-coupled receptor 8

Androgen receptor gene: linked with excessive GGN and CAG repeats. Responsible for abdominal translocation of testes. Its most crucial role is the masculinization of the genitofemoral nerve (Amann and Veeramachaneni 2007).

HOXA10: Homeobox A10. Most likely affects testicular descent in the same manner as INSL3.

GNRHR: gonadotropin-releasing hormone receptor

ESR1: oestrogen receptor


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Methods of Eradication

  • Bilateral cryptorchids are sterile
  • Unilateral cryptorchids are urged not to be used for breeding, especially in predisposed breeds
  • Orchiopexy: surgical extraction of the undescended testicle(s).
  • Spontaneous descent seen shortly after birth and just after puberty
  • Virility highly affected by disease: its presence alone decreases the chance of being passed down.

Works Cited

Romagnoli S.E. (1991) Canine cryptorchidism. Vet. Clin.

North Am. Small Anim. Pract., 21, 533–544.

Mueller, P. O. E., and A. H. Parks. "Cryptorchidism in Horses." Equine Veterinary Education 11.2 (1999): 77-86. Web.

HAYES, H. M. (1986), Epidemiological features of 5009 cases of equine cryptorchism. Equine Veterinary Journal, 18: 467–471. doi: 10.1111/j.2042-3306.1986.tb03692.x

Yates, D ; Hayes, G ; Heffernan, M ; Beynon, R. "Incidence of cryptorchidism in dogs and cats"

The Veterinary record, 19 2003, Vol.152(16), pp.502-4

Amann, R. P., and D. N R Veeramachaneni. "Cryptorchidism in Common Eutherian Mammals." Reproduction 133.3 (2007): 541-61. Web.

Yates, D., G. Hayes, M. Heffernan, and R. Beynon. "Incidence of Cryptorchidism in Dogs and Cats." Veterinary Record 152.16 (2003): 502-04. Web.

Virtanen, H.e., and J. Toppari. "Epidemiology and Pathogenesis of Cryptorchidism." Human Reproduction Update 14.1 (2007): 49-58. Web.

Discussion Question

A case of congenital unilateral cryptorchidism followed by a spontaneous descent three months after birth occurs. As his physician knowing the testicular complications and genetic involvement of cryptorchidism, would it be appropriate to warn against having children due the possibility of inheritance? What moral and ethical implications would this warning have on his "reproductive freedom"?