Polydactyly is characterized by the presence of more toes than usual, usually due to genetic mutations affecting the expression of the Shh gene. This condition, which can involve one or more limbs, has been observed in several feline breeds and lines, including Hemingway cats in North America and UK cats with UK1 and UK2 variants.
Symptoms
Polydactyly is characterized by the presence of more than 18 toes at birth, and these extra toes may appear on the front or hind legs or both. Combinations of extra digits vary considerably and do not follow a continuous pattern. The extra digits include muscle and bone, although they usually lack the radial sesamoid bone. In addition to the additional number of digits, affected cats may also show an altered, but not detrimental, conformation of the carpus and tarsus.
Disease Management
The management of polydactyly in cats generally does not require medical intervention, as this condition rarely causes health problems.
Genetic basis
This disease follows an autosomal dominant mode of inheritance. Autosomal dominant inheritance means that cats only have to inherit one copy of the mutation or pathogenic variant to be at risk of developing the disease. Each kitten born to a parent carrying one copy of the mutation has a 50% chance of inheriting one copy of the mutation and being at risk for the disease. Breeding between cats carrying genetic variants that can cause disease is not recommended, even if they do not show symptoms.
Technical report
Polydactyly in cats is a genetic condition in which cats have extra toes on their paws. This anomaly is due to mutations in the conserved regulatory element ZRS (Zone of Polarizing Activity Regulatory Sequence) that controls the expression of the Sonic Hedgehog (Shh) gene during limb development. ZRS is a long-range regulator that plays a crucial role in finger formation and differentiation. In cats, three specific mutations have been identified that cause polydactyly: the Hw mutation, found in Hemingway cats in North America, and two mutations in the United Kingdom, UK1 and UK2. These mutations involve the substitution of a single base pair at positions 479 (Hw), 257 (UK1) and 481 (UK2). These alterations modify the expression of the Shh gene in the limb bud, resulting in the formation of additional fingers. In this case, we analyzed the Hw variant, where it has been observed that cats carrying this mutation usually present polydactyly only in the forelimbs.
Most affected breeds
Pixiebob
Domestic Shorthair
Maine Coon
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