Polydactyl cats have extra toes, setting them apart from standard felines, which typically have eighteen digits (five on each front paw and four on each back paw). This phenomenon, known scientifically as polydactyly, is a naturally occurring physical anomaly that can appear in any domestic cat population; it is not specific to any breed.
Understanding the Extra Toe
The presence of additional digits is the defining characteristic of polydactyly, with some cats exhibiting up to nine toes on a single paw. The extra toes are most commonly found on the front paws, though they can sometimes appear on the hind paws as well.
One recognized form is pre-axial polydactyly, where the extra toe appears on the medial side of the foot, often giving the impression of a thumb. This configuration results in the popular nicknames “mitten paws” or “thumb cats.” Another type, post-axial polydactyly, involves the extra digits being located on the outer side of the paw.
The extra toe can range from a small, soft tissue growth to a complete, fully-formed digit with its own bones, claws, and muscle structure. The condition is present from birth and is generally a benign variation in the cat’s anatomy.
The Dominant Genetic Cause
The root cause of feline polydactyly is a specific genetic mutation that alters limb development during the embryonic stage. This condition is inherited as an autosomal dominant trait, meaning a kitten only needs to inherit one copy of the mutated gene from either parent to exhibit the extra toes. If one parent is polydactyl, there is approximately a fifty percent chance that each kitten in a litter will inherit the trait.
The mutation is not found within the gene that codes for the limb structure, but in the ZPA Regulatory Sequence (ZRS). The ZRS is an enhancer element located within the LMBR1 gene, situated near the Sonic Hedgehog (Shh) gene, which is crucial for establishing the pattern and number of digits in the developing limb.
A mutation in the ZRS enhancer causes it to become overactive or activate at the wrong time. This leads to the ectopic, or misplaced, expression of the SHH signaling protein in the anterior portion of the limb bud. The resulting abnormal concentration of the SHH protein disrupts the normal developmental blueprint, causing the limb to form additional digits.
Polydactyly in History and Geography
The unique anatomy of polydactyl cats played a role in their historical spread across the globe. These six-toed felines were highly valued by sailors, who kept them as ships’ cats on long voyages. The extra digits were believed to provide superior grip and balance, making the cats more sure-footed on pitching decks.
Sailors also appreciated the cats’ reputation as exceptional mousers, which helped control rodent populations. The maritime connection is a primary reason why polydactyl cats became concentrated in port cities, particularly along the East Coast of North America and in parts of Great Britain. Boston, Massachusetts, is a notable epicenter for the trait’s dispersion.
The author Ernest Hemingway was the most famous champion of the polydactyl cat, having received a six-toed cat named Snow White from a ship captain. Hemingway’s affection led to a large colony of its descendants residing at his former home in Key West, Florida. Consequently, polydactyl cats are often affectionately referred to as “Hemingway cats.”
Daily Care and Health Implications
Polydactyly does not pose any significant health risk to a cat, and these animals live normal, healthy lives. However, the presence of extra toes necessitates specialized considerations for routine care.
The extra claws can sometimes be poorly aligned, preventing them from being naturally worn down during walking or scratching. Diligent and regular nail trimming is required to prevent the extra claws from growing too long.
If left untrimmed, these claws can curl and grow inward, potentially embedding themselves into the paw pad, which causes pain, lameness, and a risk of infection. Owners should routinely inspect the extra digits for any signs of redness, swelling, or discomfort.
In rare instances, the genetic mutation can lead to more complex skeletal abnormalities, such as severe paw deformities or radial hypoplasia. These serious cases may require veterinary intervention, including specialized care or surgical removal of a severely malformed digit to prevent ongoing pain.