LUA vs. HUA
What’s the physiological difference?
SLC2A9 (Exon 5) is the canine gene responsible for converting uric acid to allantoin - an inert substance that is then excreted in the urine. Before the LUA Backcross Project reintroduced the normal gene, all Dalmatians were High Uric Acid (HUA) and had two recessive genetic mutations of SLC2A9 (Exon 5). This means all HUA Dalmatians had the hyperuricosuria disease and created excessive amounts of uric acid and were at risk of forming dangerous kidney and bladder stones. Low Uric Acid (LUA) Dalmatians have normal levels of uric acid and they are not prone to forming the kidney and bladder stones and other problems that can be caused by hyperuricosuria.
What’s the genetic difference?
It is postulated that the recessive genetic mutation became ‘fixed’ in the Dalmatian long ago as Dalmatian breeders selectively bred their dogs for the spotting pattern that is known and loved today. It is also believed that at least one of the genes responsible for spot size and solid density is in close chromosomal proximity to the SLC2A9 (Exon 5) gene. As breeders selected for large, round, solid spotting patterns, they unintentionally selected for the genetic mutation for hyperuricosuria.
Thankfully, the mutation is inherited from a simple recessive gene - meaning the normal gene is dominate and can be reintroduced to produce LUA Dalmatians. All chromosomal genes come in pairs, one is inherited from the father and the other is inherited from the mother.
HUA Dalmatians are often referred to by breeders as hu/hu - meaning they have two HyperUricosuria genes. LUA Dalmatians are referred to as N/hu (if they have one of the normal genes in question) or N/N (if they have two copies of the normal gene in question).
If an HUA Dalmatian (hu/hu) is bred with an LUA Dalmatian with one normal gene (N/hu), then a breeder can statistically expect 50% of the litter to be HUA (hu/hu) and 50% to be LUA (N/hu). Puppies that are HUA should be fed low-purine diets and receive proper hydration so they can lead happy, healthy lives. Puppies that are LUA have no purine-related diet restrictions and are not at risk of developing kidney or bladder stones.
If two LUA Dalmatians - both with one normal gene (N/hu) - are bred, then a breeder can statistically expect 25% of the litter to be LUA (N/N), 50% of the litter to be LUA (N/hu), and 25% of the litter to be HUA (hu/hu).
If two LUA Dalmatians - one with two normal genes (N/N) and the other with one normal gene (H/hu) - are bred, the litter will be 100% LUA and statistically 50% of the litter will have two normal genes (N/N) and 50% of the litter will have one normal gene (N/hu).
An LUA with one normal gene (N/hu) is called a ‘carrier’ - meaning that it has the potential to pass both normal and mutant genes on to its offspring.
If two LUA Dalmatians - both with two normal genes (N/N) - are bred, then 100% of the litter will have two normal genes (N/N) and can only pass the normal gene on to their offspring.
The normal gene is dominate, meaning that an N/N LUA and an N/hu LUA are the same in regards to uric acid production. It is also important to note that some HUA Dalmatians are at a greater risk of developing stones than other HUAs. The reason for this is not entirely known. Likewise, males are at a statistically greater risk for urinary obstruction than females because the male urethra narrows in the penis. Urinary obstruction is an emergency that must be treated surgically.
ArmySoldier Dalmatians is proud to be a part of the LUA Breeding Program that is reintroducing the normal uric gene back into this cherished breed.