Research

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Scientific studies and empirical experience provide abundant evidence that the polydactyl trait in the Maine Coon is an innocent variance that poses no threat to the well-being of the cat. Over time, more and more is discovered about the specific mechanisms of the genetics of polydactyly. In 2008, Lettice, et al, reported that the polydactyl trait in cats is not due to a gene mutation or a (Pd) gene but rather to a single point mutation of the regulatory element responsible for expression of the  gene that determines digit formation (see specifics below). While their terminology may be dated, earlier studies and research remains valuable for the observations they provide.

In 1947 The Danforth Studies of a largely in-bred population from two DLH Dams produced 254 poly kittens which were observed and logged: “The trait is not related to sex, and no evidence is found that its gene is lethal”. Danforth found no evidence of split foot or radial hypoplasia (also called radial hemimelia) in his studies. 

2008, Laura A. Lettice, Alison E. Hill, Paul S. Devenney and Robert E. Hill from the MRC-Human Genetics Unit, Western General Hospital in Edinburgh U.K. 

This  paper investigated polydactylism in the feline world, in an attempt to  expand knowledge of the currently known genes that produce polydactyl expression in various species, including humans, mice and cats. The feline study identified three mutations of polydactyly that were similar but that had slightly different expressions. It was found that the polydactyl trait in cats is not due to a gene mutation or a (Pd) gene but to a single point mutation in a sonic hedgehog cis-regulator element known as ZRS. Sonic hedgehog (Shh) is the gene that determines digit formation, and is regulated by a non-coding ZPA regulator sequence (ZRS) which is a distant cis-element in cat’s DNA. This information not only revealed a previously unknown mechanism of control, but brought the total number of identified genetic expressions of polydactylism to thirteen, three of which were specifically associated with cats. Although noted in the study that polydactylism can be a problem in other species, no issues were found in the feline world. Subjects included pedigreed Maine Coons, as well as pedigreed Pixie Bobs and British Cats. All three mutations were benign expressions of polydactyly. The study concluded that: “Analysis of polydactylous cats identified three new mutations…we submit that this type of polydactyly has no further detrimental effect on the cat’s health”. Human Molecular Genetics, 2008, Vol. 17, No. 7 978–985 

2011, Alexia Hamelin: La Polydactylie du Maine Coon – École Nationale Vétérinaire d’Alfort. Ms.  Hamelin published as her dissertation the first analysis worldwide on  pre-axial polydactyly combining genetic and phenotypic data.  Approximately 100 polydactyl cats were examined, with the majority (86)  being Maine Coons. Sixty cats were analyzed genetically and sixty by  X-ray. Sixteen Maine Coons of American lineage demonstrated the mutation  type first reported  by Lettice et al in 2008. In forty-one Maine Coons  of Canadian lineage, however, the specific mutation could not be  identified but was not part of the cis-regulatory mechanism described  previously. This study supported earlier suppositions that polydactyly  in Maine Coons is an autosomal-dominant trait with complete penetration  and high variability. Empirical tests of reproduction, body height,  peri-natal, mortality and malformation showed no significant statistical  differences between polydactyl and non-polydactyl Maine Coons. This  data leads to no concerns for the morphology or health of the cats. The  mutation is a purely aesthetic modification passed on in dominant  autosomal mode and with variable expression or outcome. La Polydactylie de Maine Coon

2013, Axel Lange, Hans L. Nemeschkal, Gerd B. Müller – Department of Theoretical Biology, University of Vienna. Research  on the genetics of the formation of the polydactyl paw continues with  this technical publication describing the molecular basis of the  formation of the polydactyl limb. The different phenotypic polydactylous  patterns of the Maine Coon are described in detail (fore and hind limb)  and the paper presents a mathematical/statistical model of how a point  mutation can result in new digits, using threshold effects in cell  states as an explanation. Biased Polyphenism in Polydactylous Cats Carrying a Single Point Mutation: The Hemingway Model for Digit Novelty

2016, Alexia Hamelin, Dominique Begon, Fabrice Conchou, Marion Fusellier and Marie Abitbol. Polydactyly  has been reported in a number of vertebrate species, including the  domestic cat. It is a common characteristic in some breeding lines of  the Maine Coon. The aim of this study was to assess the limb phenotype  of polydactyl cats using physical and radiographic examinations.  Physical examination and radiography were used to characterize the  polydactyly phenotype in a cohort of 70 Maine Coon cats, including 48  polydactyl cats from four different breeding lines from Europe, Canada  and the USA. The phenotypic expression of polydactyly showed great  variability, not only in digit number and conformation, but also in the  structure of the carpus and tarsus. Comparison of the size of the radius  in polydactyl and non-polydactyl 3-month-old kittens and adult females  did not reveal any difference between polydactyl and non-polydactyl  cats. Conclusions: polydactyly in Maine Coon cats is characterized by  broad phenotypic diversity. Polydactyly not only affects digit number  and conformation, but also carpus and tarsus conformation, with no  apparent deleterious consequence on feline welfare.

Clinical characterisation of polydactyly in Maine Coon cats. 

2017, Axel Lange, Gerd B. Müller – Department of Theoretical Biology, University of Vienna The  occurrence of supernumerary digits or toes in humans and other  tetrapods has attracted general interest since antiquity and later  influenced scientific theories of development, inheritance, and  evolution. Seventeenth-century genealogical studies of polydactyly were  at the beginning of an understanding of the rules of inheritance.  Features of polydactyly were also part of the classical disputes on the  nature of development, including the preformation-versus-epigenesis and  the  atavism-versus-malformation debates. In the evolutionary domain,  polydactyly was used in the criticism of the gradualist account of  variation underlying Darwin’s theory. Today, extra digit formation plays  a role in the conceptualization of gene regulation and pattern  formation in vertebrate limb evolution. Recent genetic, experimental,  and modeling accounts of extra digit formation highlight the existence  of nongradual transitions in phenotypic states, suggesting a   distinction between continuous and discontinuous variation in  evolution. Polydactyly in development, inheritance, and evolution

2020, Alexia Hamelin et al. Polydactyly  has been described in two breeds of domestic cats (Maine Coon and Pixie  Bob) and in some outbred domestic cats (eg, Hemingway  cats). In most  cases, feline polydactyly is a non-syndromic preaxial polydactyly. Three  variants located in a regulatory sequence involved in limb development,  named ZRS (zone of polarising activity regulatory sequence), have been  identified to be responsible for feline polydactyly. These variants have  been found in outbred domestic cats in  the UK (UK1 and UK2 variants) and in Hemingway cats in the USA (Hw variant). The aim of this study was to characterise the genetic features of polydactyly in Maine Coon cats. 

Genetic heterogeneity of polydactyly in Maine Coon cats