Polydactyly / preaxial polydactyly DC-2 (LMBR1 regulatory) - Dog

What does this test examine?

This genetic test analyses the DC-2 variant g.19380592C>T in the regulatory LMBR1/ZRS region. This region is part of an enhancer that controls expression of the developmental gene SHH during limb formation. The trait is described as polydactyly, preaxial polydactyly, PPD, DC-2 or extra dewclaws.

What does polydactyly mean?

Polydactyly means that a dog develops extra toes or extra dewclaws, especially on the hind limbs. In the DC-2 form, a developmental variant can restore expression of the first digit, which was largely lost during canine evolution. Expression can vary: some dogs have a clear extra toe, while others mainly show an extra claw or partially developed digit.

Inheritance and result

The DC-2 variant acts in an autosomal dominant manner. One copy can be sufficient to produce the trait. Because this is a regulatory variant, the result is best interpreted together with breed, visible phenotype and breeding goal.

• Clear: the DC-2 variant was not detected.
• Positive heterozygous: one copy is present and can cause extra toes or dewclaws.
• Positive homozygous: two copies are present and the dog will pass the variant to all offspring.

Practical value of this test

For breeders, the test helps assess polydactyly beyond visible appearance. It clarifies whether a dog carries the DC-2 variant even when expression is subtle or variable within a line. This supports mating plans, explanation of extra dewclaws in offspring and management of lines where the trait is desired, accepted or unwanted.