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Reproductive Genetic Abnormalities in Dogs

Sexual development disorders in dogs occur due to errors in the genetic coding, which involve the chromosomes responsible for development of the sex organs - including the gonads (the male and female reproductive organs) - or when errors in gene development result in abnormal sexual differentiation, making it difficult to distinguish between male and female animals. Sexual disorders tend to be breed specific.

Symptoms and Types

This condition is usually caused by disorders affecting the chromosomes that determine the traits of a dog's sexual function. Gonadal disorders affect the reproductive organs, and phenotypic disorders affect the physical and biochemical reproductive properties of the dog. The signs and symptoms of gonadal or reproductive sexual development disorders may include having an unusually large clitoris, for the female, or having an undescended testicle, for the male. Other unusual reproductive organ characteristics may also be present.

Signs and symptoms of chromosomal sexual development disorders may include defects in the number of sex chromosomes. In the process of genetically screening your dog, your veterinarian may find an abnormal number of X or Y chromosomes in your dog's genetic make-up.

Signs and symptoms of phenotypic sexual development disorders may include external reproductive organs that do not match the internal chromosomes. A dog that carries male chromosomes for example, may appear to have feminine external genitalia, or a smaller than normal penis. Some animals may possess a normal reproductive organ, but also have an additional, sometimes functional, very small second reproductive organ of the opposite gender.

Causes

Sexual development disorders most commonly occur because of inherited traits or because of external causes, like the administration of toxins to the pregnant female parent (such as hormones) during pregnancy. Risk factors may also include the ingestion or administration of male or female hormones, like progesterone, during pregnancy.

Diagnosis

These types of disorders are very rare, mainly limited to specific breeds of animals, including Boston terriers and miniature schnauzers. Sexual development disorders are often apparent from birth, especially if they affect the reproductive organs and involve overly large or small reproductive organs. Individual animals that are normal in appearance, with normal external reproductive organs and abnormal chromosomes, may not be identified until they reach their reproductive years.

Diagnosis may not occur until attempts are made to breed the animal. During this time other diagnoses to rule out may include infertility, hormonal problems, including hypothyroidism, testicular problems, including degeneration, and poor timing during breeding.

Once the above conditions are ruled out, your veterinarian may carry out tests to measure hormone levels, and may conduct tests to define chromosomal sex characteristics to see whether abnormalities exist in the sex chromosomes. Physical tests will include making note of the shape and size of the reproductive organs for comparative purposes, to confirm whether any external abnormalities exist.