Testing of dogs: White spotting

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Usual turnaround time: 7 business days
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White spotting in dogs

Changes in the dog coat colour were probably one of the first novel traits that appeared during the domestication.  It is known from written records and pictures of dogs that white spotting in dog´s coat occurred several thousand years ago.  The wide variety of white spots within and between dog breeds is caused by genetic factors and stochastic effects during the melanocyte development. White spotting indicates an absence of melanocytes in the hair follicles or skin.

There has been defined a new gene locus S, localised with the MITF gene, associated with the white spotting in dog coat. The MITF encodes a transcription factor that controls the development and migration of melanocytes.  The expression of MITF protein is therefore a substantial factor in coat pigmentation.  The loss of pigment is caused by the absence of melanocytes and not by missing biochemical reactions required for pigment synthesis.

There have been described 4 different alleles at S-locus which result in a variety of phenotypes:

  • Single-coloured, solid colour without white pattern (S, Solid)
  • Small white spots, often present as a white collar or a white belly, e.g. in Bernese Mountain Dog or Basenji (si, Irish spotting)
  • Extensive white spots, e.g. in Beagles or Fox Terriers (sp, Piebald-coloured)
  • Extreme white spots, complete white coat (sw, White)

The white spotting is associated with 4 mutations: three mutations are associated with MITF-M promoter (SINE-insertion, SNP # 21 mutation, variable length polymorphism - Lp) and one with MITF-1B (12 base pair deletion in exon 1B). None of these mutations is a casual mutation for extreme white spotting. The phenotype is a result of several mutations in MITF region.

Genomia laboratory offers a genetic test for detection of mutation g.21836232_21836427ins>del  in MITF gene. Due to this mutation a short interspersed nucleotide element i.e. SINEC-Cf element is inserted. The dogs with inserted SINE have either extreme white spots (sw/sw) or piebald colour (sp/sp). The SINE insertion is absent in Irish spotted (si/si) and solid (S/S) dogs.

It seems that mode of inheritance of these mutations is autosomal semi-dominant.  Homozygous dogs carrying both copies of the mutation (acquired from both parents) have extreme white spotting (sw/sw) and heterozygous dogs (with one copy of the mutation) have either solid colour or white spots, so-called Flash (S/sw). Flash is often called Pseudo-Irish spotting, because it is very similar to Irish spotting.

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Usual turnaround time: 7 business days
1 test price: 38.00 $ without VAT