Sexual Development Disorders in Dogs

Sexual differentiation begins with fertilization. Like humans, female dogs inherit two X chromosomes, while male dogs inherit an X and a Y chromosome. After chromosomal differentiation, hormone differences in utero control the development of the organs associated with each sex, including the uterus, vagina, vulva, and clitoris in females, and the penis, testes, and scrotum in males. A problem at any point along the way can result in a Developmental Sexual Disorder (DSD). Disorders that occur in chromosomal differentiation will give the dog an abnormal number of chromosomes. Dogs with extra chromosomes may appear normal, or they may have ambiguous genitalia. If the problem occurs during development, dogs will have normal chromosomes but may have the opposite sex organs than that which is typically associated with their chromosomes, called complete or partial sexual reversal. Dogs with sexual reversal are usually infertile, and they may also have ambiguous or hermaphroditic sexual organs. Hyperplastic genitalia are typical with all types of DSD, including an enlarged clitoris, an abnormal penis, and complete or partially retained testes. Some dogs have chronic irritation of the genitals. Others exhibit no abnormal symptoms until their owners try to breed them. DSD can occur as a direct mutation (often the case with abnormal chromosome differentiation), an inherited condition in some breeds, or environmental factors during development such as pregnant dams being exposed to sex steroid hormones. DSD is relatively rare in dogs.

Disorders of sexual development can cause infertility and abnormalities in the genital organs of dogs. This can be either inherited or due to environmental factors during pregnancy. DSD usually becomes apparent during a dog’s first breeding season.

These are some of the symptoms you might notice in dogs with DSD.

• Enlarged clitoris
• Smaller or abnormally shaped penis
• Penis in female dogs
• Lack of normal sexual organs
• Genital irritation
• Infertility

Types

There are several different types of DSD.

Sex Chromosome DSD (abnormality in chromosome differentiation) 

• Rather than the typical XX (female) or XY (male), dogs inherit an abnormal set of chromosomes
• Trisomy can result in either an XXY or XXX combination, while monosomy (one chromosome) is typically X0
• Chimerism is when dogs inherit two full sets of chromosomes (XX/XX or XX/XY)

XY DSD (pseudohermaphrodites)

• Dogs have a normal set of male chromosomes, but the sex organs may be hypoplastic (fail to differentiate and develop normally)
• Ovarian tissue or a partial uterus may be present
• An inherited condition is known to affect Miniature Schnauzers.

XX DSD (pseudohermaphrodites or true hermaphrodite) 

• Dogs with an XX chromosome set may have partial or complete male sex organs, or have a combination of female and male sex organs 
• Incidents have been found in 28 breeds, including American Staffordshire Terrier, Beagle, American Cocker Spaniel, German Shorthaired Pointer, Miniature Pinscher, Norwegian Elkhound
• Pseudohermaphrodite development may have an environmental origin, if dams are exposed to sex steroid hormones during pregnancy. 

Retained testes (cryptorchidism) 

• The testes are retained inside the body either in the normal place or ectopically
• This may be part of abnormal chromosome differentiation or development, or it can occur as an isolated incident
• Retained testes atrophy over time and can develop cancer
• Boxer, Cairn Terrier, Chihuahua, Bulldog, Maltese, Miniature Dachshund, Miniature Poodle, Miniature Schnauzer, Pekingese, Pomeranian, Shetland Sheepdog, Toy Poodle, Yorkshire Terrier

There are three main causes for DSD in dogs.

• Inherited
• Environmental
• Idiopathic (unknown)

Some abnormalities may be detected on a physical examination if the clitoris or vulva is enlarged or if there is an abnormal penis. Skin irritation or dermatitis, which is common with hypoplastic organs, will also be obvious. The veterinarian may take cultures to evaluate for concurrent infection and other possible causes (pyometra, a severe uterine infection, is more likely with an abnormally developed uterus).

X-rays or ultrasound will check for internal abnormalities, such as retained testes, as well as the presence of cancerous tumors. Exploratory surgery may determine the extent to which your dog has ovarian or testicular tissue. Many dogs with DSD have a combination of both. Blood and urine tests will typically be normal unless other diseases or infections are present. The veterinarian may also test your dog’s sex steroid hormones, which are generally below normal with DSD. Karyotyping will be used to identify disorders with abnormal chromosomes.

Your dog’s breeding history can be important. Most DSD becomes evident around a year old when dogs are first bred unless the sexual organs are very noticeably abnormal. In older dogs, abnormal sex organs and infertility might be due to a different cause, such as exposure to sex hormone medication, or testicular or ovarian cancer. Breed and family history can also be relevant since DSD often runs in families.

Spaying or neutering is the recommended treatment for DSD in dogs. An ovariohysterectomy or a gonadectomy will remove any abnormal tissue or retained testes. The veterinarian will usually remove enlarged clitorises or abnormal penises at the same time, especially if there is pain or irritation in this area. Penal reconstructive surgery could be needed for male dogs with the urethra in an abnormal place as a result of DSD. 

Depending on your dog’s exact anatomy, surgery is likely to be similar to a typical spaying operation. Your dog will probably spend a day in a veterinary hospital after the operation. Pain medication may be prescribed and you will need to keep any incisions clean and dry. A period of reduced activity will last about two weeks. You may need to return for a check-up or to remove stitches. If your dog is not healthy enough for surgery, creams and pain medication may be prescribed to manage any genital irritation.

Most dogs with DSD are infertile but otherwise they still make good pets and can live relatively normal lives. Spaying or neutering is recommended since DSD usually comes with an increased risk of infection and/or cancerous neoplasia. Occasionally dogs with DSD from abnormal chromosomes can be fertile. If this is the cases, and your dog isn’t experiencing any genital irritation or other problems, treatment may not be needed. This will depend on the advice of a veterinarian.