UC Davis School of Veterinary Medicine Veterinary Genetics Laboratory

Dog Coat Color Dilute(Blue)

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A recessive mutation d1, previously named d, in the melanophilin (MLPH) gene (g.48121642G>A, c.-22G>A) was identified as the cause of color dilution phenotypes in several dog breeds (Drögemüller et al. 2007). However, this mutation alone does not account for all dilute color phenotypes. Recently, Bauer et al. (2018) identified a second dilution MLPH variant d2 (c.705G>C, p.Gln235His) in the Sloughi, Chow Chow and Thai Ridgeback dogs. Analysis at the Veterinary Genetics Laboratory (VGL) determined that the d2 variant is present at a frequency of less than 1% in phenotypically dilute French Bulldogs thus suggesting that additional variants also cause this phenotype. Subsequent research at the VGL identified a third very rare dilution variant d3 in Italian Greyhounds and Chihuahuas (Grahn et al. 2019).


Two copies of any of the three dilution variants, or any combination of two of these variants, are necessary to lighten the color. The d1 mutation is known to cause areduction in the amount of full-length protein product thus producing less pigment. The effect of the d2 mutation on the resultant protein is unknown although in the homozygous state it dilutes color. The phenotype produced by two copies of the d3 variant is unknown but this mutation is predicted to shorten the MLPH protein and likely disrupt function. Dogs that are heterozygous d2/d3 or d1/d3 have a dilute phenotype. The VGL offers a diagnostic DNA test for all three known variants of the MLPH gene.

NOTE: The known variants d1, d2 and d3 do not account for all color dilution in some breeds such as Doberman Pinscher, French Bulldog, Italian Greyhound, and English Bulldog. This means that there are still unknown mutations that dilute color which need to be investigated. In these breeds, and likely others, some dogs may carry one known and one unknown dilution mutation and present a dilute phenotype.

Results reported as:

D/D

No known dilution variants present

D/d1

Carries 1 copy of the dilution variant

D/d2

Carries 1 copy of the dilution variant

D/d3

Carries 1 copy of the dilution variant

d1/d1

Dilute, 2 copies of the dilution variants

d2/d2

Dilute, 2 copies of the dilution variants

d3/d3

Dilute, 2 copies of the dilution variants

d1/d2

Dilute, 2 copies of the dilution variants

d1/d3

Dilute, 2 copies of the dilution variants

d2/d3

Dilute, 2 copies of the dilution variants

 

Reference:

Bauer A, Kehl A, Jagannathan V, Leeb T. (2018) A novel MLPH variant in dogs with coat colour dilution. Animal Genetics 49:94-97.


Drögemüller C, Philipp U, Haase B, Günzel-Apel A-R, T Leeb. (2007) A noncoding melanophilin gene (MLPH) SNP at the splice donor of exon 1 represents a candidate causal mutation for coat color dilution in dogs. Journal of Heredity 98(5):468-473.


Grahn RA, Grahn JC, Colangelo, JR, Malvick J. A novel MLPH mutation results in a third coat color dilution variant in dogs. 10th International Conference on Canine and Feline Genetics and Genomics. Bern, Switzerland, May 26-29, 2019.

Veterinary Genetics Laboratory, Tel 530-752-2211, Email VGL