Dalmatians and Urate Bladder Stones
Dalmatians suffer from a problem that is not shared by other breeds. They are all susceptible to forming urate stones and crystals from the high concentration of uric acid in their bladders.
These stones and crystals may obstruct the flow of urine. This is an extremely painful and potentially lethal condition. If veterinary help is not found quickly, the dog may die of a burst bladder.
The Gene for Uric Acid Metabolism
The canine digestive system has evolved so that certain proteins called purines are metabolised into uric acid. Uric acid is then converted into allantoin which is excreted without harm. The gene responsible for doing this is SLC2A9.
The Gene for High Uric Acid (HUA)
In the Dalmatian, SLC2A9 has undergone a mutation and no longer functions. Uric acid is not converted into harmless allantoin. Instead it accumulates in the urinary tract—most notably the bladder—and creates a condition known as hyperuricosuria in which the level of uric acid is so high that it may form urate crystals. The mutation that causes this is called the HUA (or High Uric Acid) gene.
Urate stones and crystals are made from uric acid. They can only form when the uric acid levels are high. Dogs without the HUA gene only form urate stones and crystals when their uric acid levels are raised by unusual circumstances such as liver shunts or reactions to certain medications. The HUA gene is also found in some Bulldogs and Black Russian Terriers, and those with two copies of it share the Dalmatian’s high level of uric acid and tendency to form urate stones and crystals.
The Inheritance of the HUA Gene
All dogs have two copies of SLC2A9. The NUA (Normal Uric Acid) version is dominant, and the mutant HUA gene is recessive. The possible combinations and their effect on uric acid levels are as follows:
| Genes inherited | Uric acid levels in bladder |
| NUA/NUA | Uric acid metabolises into allantoin, levels in urine stay low |
| NUA/HUA | Uric acid metabolises into allantoin, levels in urine stay low |
| HUA/HUA | Uric acid unchanged, levels in urine rise |
This is the same way that the simple recessive gene for liver spotting (b) works. Two copies of bb are necessary for a liver Dalmatian to be produced. Bb or BB results in a black-spotted Dal.
Dalmatians’ Inheritance
Although some Bulldogs and Russian Black Terriers carry the mutant gene, many carry the NUA version. By using genetic testing to select appropriate sires and dams, breeders can ensure that all the pups they produce have normal uric acid levels. This is not, unfortunately, true of Dalmatians. Back in 1938, scientists determined that all Dalmatians carried two copies of the HUA gene and were susceptible to forming urate stones and crystals. We were unlucky that an important gene for spotting was situated next to the HUA gene, and genes next to each other tend to be inherited together. As past breeders selected for better spots, they unknowingly also selected for high levels of uric acid.