Double Merle - Australian Shepherds
Introduction to the Disorder
- May be incorrectly referred to as "lethal white"
- Gene identification occurred in 2006
- Seen in other breeds, but is commonly found in the Australian Shepherd
- Offspring come from the mating of two merle Australian Shepherds
- Banned from various dog breed clubs including the UK Kennel Club
Merle versus Double Merle
"Merle is a pattern of irregularly shaped areas of diluted pigmentation" (Brash and Kaelin 135).
Australian Shepherds that display mild to moderate dilution of the coat are considered Merle.
- These dogs are unlikely to suffer from health issues due to pigmentation
Double Merle Australian Shepherds have severe dilution of the coat leading to a mostly white coat.
- Often affects the pigmentation of the inner ear and irises
Possible Signs and Symptoms (Why is it a problem?)
- Mostly White Coat
- Visual Impairment
- Hearing Impairment
Training is possible to help with quality of life.
Autosomal Incomplete Dominance
- Merle Australian Shepherds - one merle allele, one solid/wild allele
- Double merle Australian Shepherds - two merle alleles
- Solid Australian Shepherd - two solid/wild alleles
Researched by Clark et al.
- Identified the merle gene as SILV (Silver locus, Pmel17)
- Caused by a SINE insertion between intron 10 and exon 11
- Leads to defective PMEL proteins which causes pigment death
As the illustration below shows:
Mating two heterozygous Australian Shepherds (M/m) yields:
- 25% chance of homozygous dominant offspring (Double Merle)
- 50% chance of heterozygous offspring (Merle)
- 25% chance of homozygous recessive offspring (Solid/Wild)
Mating a heterozygous Australian Shepherd to an homozygous recessive Australian Shepherd yields:
- 50% chance of homozygous recessive offspring (m/m)
- 50% chance of heterozygous offspring (M/m)
No fixed phenotype, though typically the coat color is primarily white
Breed standards - Australian Shepherd coat which is 1/3 or more white in color is a possible means for disqualification.
The UK Kennel club announced a ban on double merle Australian Shepherds in 2012.
The double merle genotype in Australian Shepherds can be prevented by prohibiting the mating of two merle Australian Shepherds (those that carry the merle allele). Unfortunately, these dogs are sought after because of their white coat. Currently, there are no regulations or laws against breeding two merle Australian Shepherds. Responsible and legitimate breeders will not breed two merle Australian Shepherds due to the risk of unhealthy puppies. However, there are irresponsible breeders and backyard breeders that purposefully breed for double merles in hopes that they come out healthy; those that are unfortunate enough to have health issues will be euthanized, given away to rescue, or even sold.
One step towards preventing this double merle breeding is for clubs, especially influential clubs such as the AKC, to follow in the UK Kennel Club's footsteps and ban the breed from registration.
Laws against the intentional breeding of two merle Australian Shepherds (and other breeds that exhibit health risk from the double merle genotype) might need to be considered as well. These puppies are being deliberately being subjected to health issues for monetary purposes. Shouldn't this be considered a form of animal abuse?
Barsh, Gregory S., and Christopher B Kaelin. “Genetics of Pigmentation in Dogs and Cats.”
The Annual Review of Animal Biosciences 1 (2013): 125-156. Web. 20 April 2015.
“Breeding Facts.” ASCA. n.p., n.d. Web. 20 April 2015.
Clark, Leigh Anne, Jacquelyn M. Wahl, Christine A. Rees, and Keith E. Murphy.“Retrotransposon Insertion in SILV is Responsible for Merle Patterning of the Domestic Dog.” Proceedings of the National Academy of Science of the United States of America 103.5 (2006): 1376-1381. Web. 20 April 2015.
“Deafness & White.” ASHGI.n.p., 2013. Web. 20 April 2015.
Sharp, C.A. “What’s Wrong with White Aussies?” ASCA. n.p., n.d. Web. 20 April 2015.
Strain, G.M., L.A. Clark, J.M. Wahl, A.E. Turner, and K.E. Murphy. “Prevalence of Deafness in Dogs Heterozygous or Homozygous for the Merle Allele.” Journal of Veterinary Internal Medicine 23 (2009): 282-286. Web. 20 April 2015.