Alopecia or Follicular Dysplasia, D Locus (Dilution)

 

Gene:  MLPH (Melanophilin)

Transmission: Autosomal, recessive

For an autosomal recessive genetic disease an animal must have two copies of the mutation in question to be at risk of developing the disease.  Both parents of an affected animal must be carriers of at least one copy of the mutation.  Animals that have only one copy of the mutation are not at risk of developing the disease but are carrier animals that can pass the mutation on to future generations.

Mutations:

American Staffordshire Terrier type mutation: Substitution, MLPH gene; c-22 G>A, exon1

Chow-Chow type mutation: Substitution, MLPH gene; c.705 G>C, p.(Q235H)

Chihuahua type mutation: Insertion, MLPH gene; c.667_668 ins.C, p.(H223P fs STOP 41)

Medical system: dermal

Breeds: American Staffordshire Terrier/Amstaff, Australian Shepherd, Barbet, Beagle, Border Collie, Cardigan Welsh Corgi, Chihuahua, Chow Chow, Doberman Pinscher, German Pinscher, Great Dane, Irish Red and White Setter, Irish Setter, Italian Greyhound, Labrador Retriever, Large Munsterlander, Miniature American Shepherd, Miniature Australian Shepherd, Miniature Pinscher, Mudi, Nova Scotia Duck Tolling, Pekingese, Pumi, Rhodesian Ridgeback, Shetland Sheepdog, Shih Tzu, Sloughi, Thai Ridgeback, Tibetan Mastiff, Weimaraner, Yorkshire Terrier

Age of onset of symptoms:  

Dilution (D locus) encodes a modifier gene for basic color pigments.  When a dog has two copies of the mutated dilution gene, it will have a diluted or paler coat color than normal.  Black coloration is diluted to blue (also called gray or slate, depending on the breed), whereas brown coloration is diluted to Isabella (also called lilac, fawn or buff, depending on the breed).  For an explanation of color genetics in dogs, visit: Dog Genetics 2.0: Colours.

Coat color dilution can be associated with a condition called alopecia or follicular dysplasia, characterized by dry skin, a dull coat and hair loss which can eventually become permanent.  Clinical signs appear around the age of 4 months and are often accompanied by recurrent bacterial infections in the hair follicles.  Although the dilution phenotype is associated with follicular dysplasia, the genetics of the disease is complex and other genes (not as yet identified) as well as environmental factors also contribute to the disease.

 

References:

OMIA link: [0031-9615]

Brancalion L, Haase B, Wade CM. (2022) Canine coat pigmentation genetics: a review. Anim Genet 53:33-34. [pubmed/34751460]

Van Buren SL, Minor KM, Grahn RA, et al. (2020) A third MLPH variant causing coat color dilution in dogs. Genes (Basel) 11(6):639.  [pubmed/32531980]

Bauer A, Kehl A, Jagannathan V, Leeb T. (2018) A novel MLPH variant in dogs with coat colour dilution. Anim Genet 49:94-97.  [pubmed/29349785]

Drogemuller C, Philipp U, Hasse B, Gunzel-Appel AR, Leeb T. (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. J Heredity 98(5) :468-473. [pubmed/17519392]

Kim JH, Kang KI, Sohn HJ, Woo GH, Jean YH, Hwang EK. (2005) Color-dilution alopecia in dogs. J Vet Sci. 6(3):259-61. [pubmed/16131833]

Schmutz SM, Moker JS, Clark EG, Shewfelt R. (1998) Black hair follicular dysplasia, an autosomal recessive condition in dogs. Can Vet J. 39(10):644-6. [pubmed/9789677]