Polydactyly (Great Pyrenees Type)

Other Names: Hind-limb-specific preaxial polydactyly, PPD
Affected Genes: ALX4
Inheritance: Autosomal Dominant
Mutation: chr18:44922455-44922505 (canFam3): 51 bp deletion
Breed(s): All Breeds
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Testing Summary

The polydactyly (Great Pyrenees type) trait test reliably determines if a dog has one of the following genotypes:

pd/pd

This dog carries two copies of the ALX4 pd Allele which is found in Great Pyrenees dogs without bilateral double dewclaws. However, polydactyly can result from variants in other genes. This dog will pass one copy of pd to 100% of its offspring.

Interpretation: Normal (typical) toes (likely no double hind dewclaws)

PDGP/pd

This dog carries one copy of the ALX4 pd allele and one copy of PDGP, the variant responsible for polydactyly and the presence of double hind dewclaws in Great Pyrenees dogs. However, polydactyly can result from variants in other genes. This dog will pass the PDGP allele to 50% of its offspring and the pd allele to 50% of its offspring, which can produce dogs with extra toes and hind dewclaws.

Interpretation: Likely polydactylous with double hind dewclaws (typical toes Carrier)

PDGP/PDGP

This dog carries two copies of the ALX4 PDGP allele, which is associated with polydactyly and the presence of double hind dewclaws in Great Pyrenees dogs. This dog will pass PDGP to 100% of its offspring and can produce dogs with extra toes and hind dewclaws.

Interpretation: Likely polydactylous with double hind dewclaws


Detailed Summary

In general, dogs have five digits on their front paws and four digits on their hind paws presumably due to evolutionary adaptation in which the first digit of the hindlimb was lost. Polydactyly (also known as canine preaxial polydactyly or PPD) refers to the restoration of the first digit in the hindlimb (known as the hind dewclaw) that was lost during canine evolution. Hindlimb polydactyly in the Great Pyrenees presents as either a single or double dewclaw with five or six digits, respectively. Great Pyrenees with single hindlimb polydactyly (five digits) did not carry the ALX4 Mutation. However, all Great Pyrenees with bilateral double hindlimb polydactyly (six digits) carry either one or two copies of the ALX4 mutation. Thus, bilateral double hindlimb polydactyly (double dewclaws) in the Great Pyrenees is associated with a mutation in the ALX4 gene and is thought to be inherited in an Autosomal Dominant manner. This ALX4 mutation has only been observed in the Great Pyrenees and was not found in numerous other dog breeds.


Testing Tips

The polydactyly (Great Pyrenees type) trait test evaluates the ALX4 gene region for the presence of the bilateral double hindlimb polydactyly associated variant. Great Pyrenees that inherit one or two copies of this "PD" variant are likely to have bilateral double hindlimb polydactyly (double hind dewclaws). Most Great Pyrenees carry one or two copies of the ALX4 Mutation. Other genetic factors are known to be associated with different forms of polydactyly in other breeds.


There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.


References

  • Fondon JW 3rd, Garner HR. Molecular origins of rapid and continuous morphological evolution. Proc Natl Acad Sci U S A. 2004 Dec 28;101(52):18058-63. [PubMed: 15596718]
  • Park K, Kang J, Subedi KP, Ha JH, Park C. Canine polydactyl mutations with heterogeneous origin in the conserved intronic sequence of LMBR1. Genetics. 2008 Aug;179(4):2163-72. [PubMed: 18689889]