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DNA Test Helps Dalmatians
Researchers identify gene that causes bladder stones


How do you recognize a Dalmatian? If you think of the movie 101 Dalmatians or the dog who traditionally rides on the fire engine, it’s easy. Dalmatians are, of course, known for their characteristic spots— breeders have spent many years selecting for dogs with spotting patterns that fit the ideal breed standard: evenly distributed, distinct, well-defined round spots that are larger than a dime but smaller than a half dollar. However, sometimes the bad unexpectedly comes along with the good. Breeding for these patterns has brought with it a predisposition to form bladder stones, a condition that is potentially life threatening. Now, with the help of a special group of Dalmatians and some dedicated breeders, scientists have unearthed the cause of this condition and designed a DNA test that will not only improve Dalmatian health, but will benefit other dogs as well.

In most dogs, the proteins in food are broken down in the liver, and the byproduct, allantoin, is excreted by the kidneys into the urine, where it dissolves. In Dalmatians, the process stops at the step before the production of allantoin; instead, uric acid is produced. Because uric acid does not dissolve well in urine, it can form urate stones in the bladder, and these stones can block the urethra; in serious cases, this condition requires surgery to resolve. The accumulation of high levels of uric acid in the urine is called hyperuricosuria (huu).

Huu, which was first described in 1916, was shown in 1938 to have a recessive mode of inheritance (an individual must have two copies of the mutation to be affected). All Dalmatians carry two copies of the huu mutation, meaning that within the purebred Dalmatian population, there is no way to breed dogs with low levels of uric acid because the trait does not exist in their gene pool. Consequently, Dalmatians produce 20 times more uric acid per day than other dogs and are prone to urate stones. (Interestingly, although all Dalmatians have high levels of uric acid, not all exhibit clinical disease. The reason for this is unknown.)

In order to correct this condition, a normal, low-uric-acid copy of the gene had to be introduced into the gene pool. In 1973, Dr. Robert Schaible, a medical geneticist and Dalmatian breeder, bred a Dalmatian to a Pointer and then bred the offspring back to purebred Dalmatians. The goal of this backcross was to produce dogs who looked and acted like Dalmatians, but who had normal (i.e., low) uric acid levels in their urine and therefore would not produce bladder stones. Each time one of these backcross Dalmatians (with low levels of uric acid, or LUA dogs) is bred to a purebred Dalmatian (with high levels of uric acid, or HUA dogs), about 50 percent of the puppies are LUA and 50 percent are HUA.

LUA dogs tend to have smaller spots than HUA dogs, providing further evidence that the huu mutation was unintentionally selected for along with the deliberate selection for spot patterns. Although the spots on LUA dogs are generally smaller, they still fall within the guidelines of the Dalmatian standard as outlined by the American Kennel Club (AKC).

Two backcross Dalmatian puppies from the fifth generation were registered with the AKC, which meant that they could be shown in AKC-recognized events. The registration was later opposed, and further registration of backcross dogs was prohibited. The issue of AKC backcross Dalmatian registration continues to be controversial and emotional. Backcross Dalmatians can be registered with the United Kennel Club.

Since most serious breeders register their dogs with the AKC, the number of purebred Dalmatians available to backcross breeders became severely limited because the puppies were not eligible for AKC registration. By 2005, after 30 years of work, few breeders were using backcross dogs in their programs, and Dr. Schaible was limited by the number of dogs he could keep himself, factors that suggested the project was nearing an end. Around that time, Denise Powell, a northern California Dalmatian breeder for more than 20 years, contacted Dr. Schaible to inquire about breeding backcross Dalmatians. “I was shocked to learn that he had just two aging stud dogs and two infant female pups,” says Powell. “I decided then and there to do what I could to help preserve the only line of LUA Dalmatians in the world from dying out. I asked, and Bob agreed to let me have one of the two pups.”



Amy Young is a geneticist at the University of California, Davis; her article on commercial DNA breed tests appeared in the Sept/Oct '08 issue of Bark.


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