When they eat purines, a class of chemicals that are found in many types of food and most abundant in organ meats and some types of fish and shellfish,, most mammals break them down into a substance called allantoin, which is then excreted. The only exceptions are humans, great apes and Dalmatian dogs, all of which instead convert purines into uric acid.
That little difference in metabolism can have significant consequences. In humans (and presumably great apes), uric acid can build up in the blood and cause gout, a painful inflammatory arthritis that results from deposition of uric acid crystals in joints. Dalmatians don’t get gout from their uric acid. For them, uric acid crystallizes in their bladders, leading to stones that often have to be removed with surgery
All pure-bred Dalmatians have the genetic mutation that causes uric acid to build up in their blood, a direct result of years of selective breeding to enhance their characteristic spotty coat. A new report, published online today in PLoS Genetics, has finally zeroed in on the mutated gene responsible: SLC2A9.
Coincidentally, but not really surprisingly, variants in SLC2A9 have also recently been linked to uric acid levels and gout in humans (23andMe customers can consult our Gout Research Report to determine their genotype at three of those variants). What is a surprising coincidence (at least to me!) is that a human sample used for one of the genomewide association studies that identified the SLC2A9 variants was from the Dalmatian Islands in Croatia.
There is hope for eliminating high uric acid levels in Dalmatians. The “Dalmatian-Pointer Backcross Project” advocates breeding pure Dalmatians with the offspring of a single Dalmatian-Pointer mix born in the 1970’s. These mixed dogs carry one normal copy of the SLC2A9 gene, inherited from the pointer. Each time a litter is produced from the mating of a pure Dalmatian with a mix, about 50% of the puppies will inherit the normal gene, while the other 50% will remain afflicted with high uric acid. Over time, by mating only dogs with the normal SLC2A9 gene, high uric acid levels should disappear.
The Backcross Project has been underway for some time, but until now it has relied on urine tests to identify puppies unaffected by high uric acid levels. Now that the exact gene mutation is known, breeders will be able to more easily identify unaffected puppies. The Veterinary Genetics Laboratory at the UC Davis School of Veterinary Medicine will soon be offering DNA testing for SLC2A9 mutations.
Photo: Raul Kaidro