Clinical characterisation of polydactyly in Maine Coon cats

Inherited non-syndromic polydactyly in a Berber and Arabian-Berber horse family

BACKGROUND

Supernumerary digits, or polydactyly, have been described in various species including humans, wild and domestic animals. In horses, it represents the most common congenital limb malformation, which has only been described in isolated cases or nuclear families. Molecular aetiology has not been reported.

OBJECTIVES

To characterise the phenotype of a non-syndromic pre-axial polydactyly in a horse family and to decipher the inheritance pattern.

STUDY DESIGN

Retrospective study.

METHODS

Forty-three members of the family including a previously reported polydactyl case were recruited. Available clinical and radiographical findings from the initial case and its family members were summarised and karyotypic examinations of the horses were performed.

RESULTS

On clinical examination, eight horses (including the previously reported case) had one or two supernumerary digits on their forelimbs and one additional case was diagnosed using radiography. Additional digits were located on the medial side of the forelimbs in all nine polydactyl horses. Radiography highlighted variable expression of the defect, which was either unilateral or bilateral. Variations were observed in the number of supernumerary phalanges, the level of development of a rudimentary metacarpal bone, the individualisation of a supernumerary digit and the existence of a rudimentary hoof. All nine affected horses were related to a single stallion. Pedigree analysis revealed that the most likely inheritance pattern was autosomal dominant with incomplete penetrance and variable expressivity. A more complex mode could not be ruled out.

MAIN LIMITATIONS

Restricted recruitment of the family members due to confidentiality constraints and to international dispersal of the relatives, quality of radiographs.

CONCLUSIONS

We describe an equine preaxial polydactyly in a Berber and Arabian-Berber family most likely with autosomal dominant inheritance with incomplete penetrance. This is the first description of an inherited non-syndromic polydactyly in horses.

Genetic Testing: practical dos and don'ts for cats

PRACTICAL RELEVANCE

A significant number of genetic variants are known for domestic cats and their breeds. Several DNA variants are causal for inherited diseases and most of the variants for phenotypic traits have been discovered. Genetic testing for these variants can support breeding decisions for both health and aesthetics. Genetic testing can also be used to monitor for the health of, or provide targeted therapy for, an individual cat and, more widely, can progress scientific discovery. Technological improvements have led to the development of large panel genetic testing, which can provide many DNA results for a low cost.

CLINICAL CHALLENGES

With the development of large panel genetic testing has come companies that can carry out this service, but which company is best to use may not always be clear - more tests are not necessarily better. Usage and interpretation of genetic data and how the results are presented by commercial laboratories may also be confusing for veterinary practitioners and owners, leading to misinterpretations for healthcare, improper genetic counseling, and poor breed and population management.

EVIDENCE BASE

The information provided in this review draws on scientific articles reporting the discovery, and discussing the meaning and implications, of DNA variants, as well as information from the Online Mendelian Inheritance in Animals (OMIA) website, which documents all the DNA variant discoveries. The author also provides suggestions and recommendations based on her personal experience and expertise in feline genetics.

AUDIENCE

This review is aimed at general practitioners and discusses the genetic tests that can be performed, what to consider when choosing a testing laboratory and provides genetic testing counseling advice. Practitioners with a high proportion of cat breeder clientele will especially benefit from this review and all veterinarians should realize that genetic testing and genomic medicine should be part of diagnostic plans and healthcare for their cat clients.

Feline Skeletal Reference Guide: A Cadaveric Radiographic Measurement on Lower Limb Extremities

OBJECTIVE

 The aim of this study was to create a feline reference database for the length, width and slenderness (length to width ratio) of metacarpal and metatarsal bones, radius and tibia.

STUDY DESIGN

 Radiographs of the radius, tibia, metacarpus and metatarsus were performed in domestic short hair cat cadavers (n = 40). Length and width of the aforementioned bones were measured in mature domestic shorthair cats and bone slenderness (length/width) and index ratios calculated.

RESULTS

 A significant skeletal sex dimorphism exists in cats, with bones of the metacarpus, metatarsus, radius and tibia generally longer and wider in male cats compared with female cats, with differences frequently significant. The most significant difference was identified for the width of Mc5 (p = 0.0008) and the length and width of Mt5 (p = 0.0005). Index ratios for length and width of radius to metacarpal bones, and tibia to metatarsal bones, were not significantly different between male and female cats, except for Mc5. The index ratio for Mc5 was significantly higher in male cats (p = 0.002).

CONCLUSION

 The present study provides insights into the normal length and width of distal forelimb and hind limb bones as well as bone index ratios in mature domestic shorthair cats. Using this information, it is now possible to quantitatively assess the relationship between these bones in domestic cats using radiography. This will assist not only with the diagnosis and categorization of skeletal abnormalities but can also guide surgical interventions of metacarpal and metatarsal bone fractures.

Genetic heterogeneity of polydactyly in Maine Coon cats

OBJECTIVES

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.

METHODS

Genotyping assay was used to identify the variant(s) segregating in a cohort of 75 polydactyl and non-polydactyl Maine Coon cats from different breeding lines from Europe, Canada and the USA. The authors performed a segregation analysis to identify the inheritance pattern of polydactyly in this cohort and analysed the population structure.

RESULTS

The Hw allele was identified in a subset of polydactyl cats. Sequencing of two regulatory sequences involved in limb development did not reveal any other variant in polydactyl cats lacking the Hw allele. Additionally, genotype-phenotype and segregation analyses revealed the peculiar inheritance pattern of polydactyly in Maine Coon cats. The population structure analysis demonstrated a genetic distinction between Hw and Hw-free polydactyl cats.

CONCLUSIONS AND RELEVANCE

Polydactyly in Maine Coon cats is inherited as an autosomal dominant trait with incomplete penetrance and variable expressivity, and this trait is characterised by genetic heterogeneity in the Maine Coon breed. Maine Coon breeders should be aware of this situation and adapt their breeding practices accordingly.

Extreme bilateral polydactyly in a wild-caught western grey kangaroo

Polydactyly is a congenital malformation resulting from an autosomal dominant mutation manifesting as supernumerary digits of the hands or feet. It is most commonly reported in humans and domestic mammals, though there have also been isolated examples across a range of wild vertebrate species. Here we report a case of extremely unusual bilateral preaxial polydactyly on the pectoral limbs of a male western grey kangaroo (Macropus fuliginosus) from the South West region of Western Australia, in which two supernumerary digits were present on each manus. A supernumerary digit I on each manus was rudimentary in morphology without extrinsic muscular connections. However, supernumerary digit II present on each manus had fully developed extrinsic and intrinsic muscular connections, suggesting that these digits possessed normal function in flexion and extension. An alternative hypothesis is that the two supernumerary digits are both representatives of the most radial digit I, though this would then require the true digit I to have taken on the appearance of digit II by acquiring an additional phalanx and modified muscular attachments. The carpal bones exhibited a number of subtle differences in morphology when compared to normal pentadactyl individuals. The presence of a distal, rather than proximal, epiphysis on the first metacarpal was unexpected but further investigation suggested that this characteristic is perhaps more variable (in this species at least) than has been previously recognized. This case provides an unusual example to be considered within the broader context of limb development.

Genetic Instability of a Polydactyl Hypopigmented Cat With Squamous Cell Carcinoma-A Case Report

Polydactyly, hypopigmentation, and squamous cell carcinoma are common in cats. However, a cat exhibiting all of these conditions has not yet been reported. This study presents the case of a 14- year-old male Mexican cat, hypopigmented, with supernumerary fingers, two preaxial and one on each posterior limb, admitted to the clinic with a lesion in the left periocular region. The cat was subjected to a general physical examination, blood, and urine chemistry, as well as a biopsy and genomic instability assessment with an analysis of the red blood cells (RBC) micronucleated erythrocytes (RBC-MNE) in the peripheral blood. The biopsy was positive for squamous cell carcinoma, and the RBC-MNE count (8.6 MNE/1000 erythrocytes) was high compared to that previously described in other domestic cats or wild cats. Thus, the genomic instability of the RBC-MNE could be used as an indicator to identify clinical conditions of felines, particularly those with one of the characteristics exhibited by this Mexican cat. The RBC-MNE test is the most widely used in the world for the evaluation of DNA damage, but to our knowledge, it has not been used to identify vulnerable non-human specimens.