Some of the concepts and language used on this site are complicated. The following information may aid understanding.
DALMATIAN URIC ACID DEFECT AND GENETICS
Most Dalmatian health surveys, veterinarian reports and research studies show that uric acid related stone disease is a problem in the Dalmatian as a Breed, and that this problem is fairly common. Different studies get different results, but overall it is thought that somewhere between fewer than 10% to as many as 30% of Dalmatians may develop stone disease during their lifetime. The exact number is a point of debate amongst breeders, vets and scientists. It is almost impossible to get a definitive answer. Why? Because the total number of Dalmatians in the population (e.g. in the United States) is not known and probably cannot ever be known.
Dalmatians have a specific genetic defect that affects the metabolism of uric acid. This was discovered nearly a century ago. In the 1930s a cross breeding of a Dalmatian to a Collie produced puppies that all had normal uric acid (and were pretty cool looking). That means that the Dalmatian must have been homozygous recessive (that means had two copies of the recessive gene). You will recognize these genetics if you think of coat color in the Dalmatian. Black is dominant. Liver is recessive. If you breed a pure for black (both copies of the gene are the same and dominant - [BB]) to a liver (both copies of the gene are the same and recessive - [bb]) the ONLY possible outcome is a black spotted puppy [Bb]. The same is true of the gene that controls uric acid metabolism [U]. Normal dogs are dominant [UU] and the Dalmatian is recessive [uu]. Breed a Collie to a Dalmatian and you can only get [Uu], or the dominant type, which is normal uric acid metabolism.
DALMATIAN URIC ACID METABOLISM AND STONES
In normal dogs, proteins in food (specifically purine proteins) are broken down by the metabolic machinery in the liver to an end product called allantoin. Allantoin is excreted into the urine by the kidney, and is soluble in the urine in the bladder (i.e., does not form crystals or stones). In the Dalmatian, the metabolism of purine proteins stops at one step earlier - at uric acid. Although the Dalmatian has the normal enzyme called uricase to metabolize uric acid to allantoin, the uric acid just cannot get to the cell for the uricase to work on because there is a missing transporter protein that is responsible for doing that. So instead, uric acid is excreted into the urine by the kidney.
Uric acid is less soluble than allantoin, and under certain concentrations and pH conditions, uric acid can come out of solution as a salt called urate. Urates can form crystals, which can clump together to form aggregates, and even bigger pieces - stones. Stones can form of various sizes, and if large enough, stones can block the urethra - the tube leading from the bladder to the outside world of the Dalmatian and onto your carpet or the grass. This blockage is much more common in male Dalmatians than females because the males have something called the os penis - a bone in their penis that is very small in caliber and can easily become blocked.
There are some environmental risk factors that increase the likelihood that urinary uric acid will form solids (stones) in the bladder, such as inadequate water intake, or if urine stays in the bladder for an extended period of time. Diets particularly rich in proteins, and specifically high in purine content (like feeding or baiting with liver) can increase the risk of increasing urinary uric acid. Sometimes local water properties can exacerbate the problem. Breeders and owners must manage the percentage of protein in the food that is provided to their Dalmatian - generally around 21% - and be cautious that the formula is relatively low in purine proteins - no liver. Adequate and liberal access to water is important, as are frequent opportunities to exercise and relieve the Dalmatian.
Although the precise causative factor for the formation of uric acid stones may not be known for a given Dalmatian, it is clear that several factors may be contributory, such as diet, water access, exercise, possibly stress, and others. A common feature though is the high level of uric acid in the urine of the Dalmatian, which has been reported to be from 400 to 800 mg/dl. This is 10 to 20 times higher than the normal canine level of about 40 mg/dl.
THE BACKCROSS THEORY & PRACTICE
The "Backcross Theory" directly addresses the high uric acid level. The theory is that if one removes the trigger substance - the high uric acid - that the formation of uric acid stones is literally cut off, because the substrate is missing. Think of this as trying to build a brick house. The Backcross Theory would prevent building the house by taking away the bricks. It doesn't matter that the mortar is there, that a bricklayer is present, and that a foundation is ready. No bricks - no brick house; simple as that. The Backcross Theory works the same way for uric acid stones. No uric acid - no urate stones.
Puppies whelped from Low Uric Acid Descendants are tested for their urinary uric acid to creatinine ratio and have been found to have a highly significant ten-fold difference in this ratio, which separates the "Lows" from the "Highs". This screening test result persists into adulthood. Ten adult LUA Descendants have been tested in the same way and found to have a persistent six-fold difference between the LUAs and the high uric acid AKC registered Dalmatians. Note that this test is used only for screening purposes, and is specifically not used as a scientifically confirmed measure of the total daily urinary uric acid production.
The categorization of puppies by spot urine testing of urinary uric acid to creatinine ratio has been confirmed to be 100% accurate by DNA testing of LUA Descendants. The specific gene on canine chromosome #3 that has been identified only exists in the LUA Descendants, and not in the HUAs or in AKC registered Dalmatians.
All present day LUA Descendants are heterozygous for the specific gene, i.e. they have one normal copy [U] and one recessive copy [u]. Their genotype is [Uu], and their phenotype is normal canine urinary uric acid, which is called Low Uric Acid - LUA. All AKC registered Dalmatians are homozygous recessive, i.e. they have two copies of the recessive gene [u], which gives them a genotype of [uu] and a phenotype of High Uric Acid - HUA.
If you breed an LUA Descendant [Uu] to an AKC registered Dalmatian [uu], theoretically 1/2 of the puppies will be [Uu] or LUA, and 1/2 of the puppies will be [uu] or HUA. Nature doesn't always follow the laws of probability and statistics, particularly in small litters of 6 or 7 puppies. There are now 7 known pure dominants that exist today [UU]. It is likely that breeding LUAs to LUAs will produce more homozygous dominants [UU] in the future.
A pedigree is a listing of all ancestors of a given dog. An 11 generation pedigree has 4,094 ancestors, and if you include the dog in question, there are 4,094 plus 1 or 4,095 dogs. The 11 generation pedigree of an LUA Descendant has 4,080 AKC registered Dalmatians, and only 10 to as many as 15 LUAs, depending on which breeding is analyzed (some line breedings were done in the past), for less than 1/2 of one percent (0.24% to 0.36%) LUA Descendants. Only one Pointer was ever used.