Polydactyly (UK2 Variant)

Polydactyly is characterized by the presence of more fingers than usual, usually due to genetic mutations affecting the expression of the LMBR1 gene.

Definition

Polydactyly in cats is a congenital deformity, clinically characterized by the presence of more than 18 total digits at birth, with the additional digit on the forelimb and/or hindlimb. It is related to the LMBR1 gene containing the regulatory element known as ZRS that controls the expression of the Sonic Hedgehog (SHH) gene in the limbs. LMBR1 ensures that SHH is expressed at the correct time and place during embryonic development, which is crucial for proper limb growth pattern.

Genetic basis

Mutations in the ZRS (such as the nucleotide change of T>A, which corresponds to the UK2 variant) act as gain-of-function mutations that activate SHH expression at ectopic sites during embryonic development, leading to the formation of additional digits. Polydactyly in cats is inherited as an autosomal dominant trait, so the presence of a single copy of the variant is sufficient to express the trait.

Other relevant information

In many cases, the extra digits are fully functional, although they may vary in size and shape. This condition has been observed in several feline breeds and lines, including Hemingway cats in North America and UK cats with UK1 and UK2 variants.

Bibliography

Lettice LA, Hill AE, Devenney PS, et al. Point mutations in a distant sonic hedgehog cis-regulator generate a variable regulatory output responsible for preaxial polydactyly. Hum Mol Genet. 2008 Apr 1;17(7):978-85.