Infertility and sterility are plaguing more than a dozen breeds of dogs, and an inherited condition called XX sex reversal (XXSR or hermaphroditism), which sometimes causes abnormal genitalia, is to blame in many cases.

Vicki Meyers-Wallen, V.M.D., a molecular geneticist in comparative medicine at the Baker Institute for Animal Health at Cornell University, seeks the help of dog owners and breeders to help her determine just how prevalent the disorder is. She hopes also to determine how the disorder is affecting breeding, identify the mutant gene to blame and develop a DNA test to diagnose and eventually breed the mutant gene out of affected breeds or bloodlines.

"Although we don't know the actual incidence of the disorder in purebreds, we know it's becoming increasingly common because we can't yet identify carriers, and it's not necessarily an easy disorder to diagnose," Meyers-Wallen said. "Currently, the only way to identify carriers is after they produce an affected offspring, which is often after they've already produced other offspring which are carriers. This makes the problem increasingly common."

So far, XXSR has caused well-documented infertility and sterility in at least seven breeds: the American and English cocker spaniel, German shorthaired pointer, Weimaraner, beagle, Kerry blue terrier and Chinese Pug. In addition, the problem has been diagnosed in the West Highland white terrier, basset hound, Doberman pinscher, Pomeranian, viszla and Walker hound but may occur in other breeds as well.

Although male dogs (with XY sex chromosomes) can be carriers, only female dogs (with XX sex chromosomes) are actually affected. Affected dogs may manifest unexplained infertility or may have genital abnormalities such as a vulva shaped like a foreskin, an enlarged clitoris that may protrude from the vulva, or a longer-than-normal distance between the anus and vulva so that the "vulva" may actually be very near the belly.

Internally, affected dogs usually develop both ovarian and testis tissue (an ovotestis) and develop abnormal reproductive tracts that are usually not obvious during a spay/neuter operation, even to experts in XXSR.

"Correct diagnosis now really depends upon microscopic examination of the ovaries by a pathologist who is familiar with XXSR. Typically, the pathologist will detect either one ovary and an ovotestis, two ovotestes or two testes that are usually in the abdomen," said Meyers-Wallen. "All affected dogs have a complete uterus, although it may be small. Many have an elongated mass (epididymis) adjacent to the ovotestis or testis."

Affected dogs have normal female chromosomes on chromosome analysis, and thus are not differentiated from normal females by this test. Meyers-Wallen's goal is to develop DNA tests to diagnose the disorder so that neither microscopic studies nor chromosome analysis will be needed.

When carriers breed with one another, only one in four offspring is likely to be affected, and two out of four are likely to be carriers. "This is a serious threat to the future of certain bloodlines or to the breed itself, but with the cooperation of owners and veterinarians and with judicious breeding selections, it might be possible to eliminate carrier-to-carrier breedings. This would, eventually, eliminate the mutant gene from a bloodline or breed," Meyers-Wallen pointed out.

Meyers-Wallen requests that dog owners of purebreds and breeders be on the lookout for unexplained infertility and abnormal genitalia. If anyone suspects a dog might be carrying the disorder or is affected, please contact Dr. Vicki Meyers-Wallen at the J.A. Baker Institute, College of Veterinary Medicine, Cornell University, Ithaca NY 14853; e-mail ; fax (607) 256-5689 or telephone (607) 256-5602 or 5683. All information will be held in strictest confidence.