Polydactyly and Radial Hemimelia
- Additional digits on paws of cats (normally have 5 on forelimbs and 4 on hindlimbs)
- Snowshoe quality - alleged benefit to weight distribution on snow
- Visibly appealing for uniqueness
- Potential link to bilateral radial hemimelia (hypoplasia/aplasia) and radial agenesis,
- Two Types:
- Preaxial (Before first phalange, common)
- Postaxial (After fourth phalange, rare)
- First appearance suggested in early 1600s
- Origin debated between Boston and England (Norway?)
- Used as mousers and good luck charms on ships in 19th century
- Documented in oil painting from 1876 (MCBFA 1970)
- Published as rumor by Darwin in 1850s.
- Currently found in North America, Europe, and Asia.
- Iconic breeds: Main Coon and Pixie Bob
- Nicknamed Hemmingway Cat from author's affinity
- Point substitution mutation of Pd gene
- Autosomal Dominant
- Ectopic expression of signaling molecule in developing limb
- Mutation located at sonic hedgehog cis-regulator, notated as ZRS (Lettice et. al. 2007)
- Variability in expression causes variability in phenotype
Genotypes (Hemmingway House)
-Approximately 50 cats currently reside at the Hemingway house.
-Approximately 50% have polydactyly
-Very little Gene Flow (most are descendants of Hemingway's original Polydactyl cat)
-Not subject to Natural Selection (no consequence to relative fitness)
-Assumed not a sexually selected trait
-Hardy-Weinberg equilibrium estimation (sample size too small to support with confidence)
p + q = 1
pp + 2pq + qq = 1
p = Polydactyl
q = normal
qq = .5 -> q = .71 -> p = .29
pp = .09
2pq = .41
Homozygous Dominant = 9%
Heterozygous Dominant = 41%
Homozygous Recessive = 50%
Of the 50 or so cats at Hemingway house, approximately 25 are homozygous recessive, 21 are Heterozygous Dominant, and 4 are Homozygous Dominant.
Size of sample increases susceptibility to genetic drift.
Uncertainty regarding origin of deformities, possibly a different mutation than harmless version of Pd mutation.
Radial Hypoplasia/Aplasia -
- Congenital underdevelopment or absence of part or all of the radius.
- Relative frequencies uncertain due to abundance of breeders who practice without regulatory oversight.
- Euthanasia without veterinary assistance, natural death or miscarriage may belie accurate data
Radial Agenesis -
- Angular deformities in affected limbs.
- Affliction in radius causes hyperplasia of Ulna, resulting in a larger diameter.
-Insufficient research linking polydactylism with radial deformities
Case Study - Auburn University
- Two 10 week old kitten littermates (male and female) presented with sibling and mother (unnafected)
- Polydactyl, radial hemmelia, radial agenesis, and cardiomegaly
- Suggestive heritiability of traits and correlation between polydactylism and corresponding deleterious symptoms
- Targeted breeding due to appeal and resulting demand from consumers
- Common Veterinary recommendations are to NOT use polydactyls for breeding
- There are no current regulations in place regarding breeding of polydactyl cats
- Cosmetic surgery for show quality
- Targeted breeding may result in inbreeding; reducing genetic variation
- Potential link with radial hemimelia may cause propagation of deformity
- Twisty Cats - radial agenesis deliberately bred to reduce cat's ability to escape
Immediate: Breeding of polydactyl cats should be restricted or ceased until sufficient evidence supports the findings of Lettice et. al.
Long Term: Breeding polydactyl cats should only be permitted if the breed stock has been certified to contain the non-deleterious version of the gene. A regulatory agency needs to be created, enforcing carriers of the 'bad' mutation to be de-sexed, and enacting punishment on non-certified breeding of polydactyl cats.
1. Danforth CH. 1947. Heredity of Polydactyly in the Cat. Oxford Journal of Heredity 38 (4): 107-112
2. Lockwood A, Montgomery R, McEwen V. 2009. Bilateral Radial Hemimelia, Polydactyly and Cardiomegaly in Two Cats. Veterinary and Comparative Orthopaedics and Traumatology (VCOT) 6: 511-513
3. Lettice LA, Hill AE, Devenney PS, Hill RE. 2007. Point mutations in a distant sonic hedgehogcis-regulator generate a variable regulatory output responsible for preaxial polydactyly. Oxford Journal Human Molecular Genetics 17 (7): 978-985
4. MCBFA Scratch Sheet, Winter Quickie 1970
10. Hemingway House data: