Polydactyly, a genetic defect that results in an increased number of digits, has historically been observed in a range of species. In cats, polydactyly is considered autosomal dominant and results from point mutations in a control region which effect the expression of the developmental gene Sonic Hedgehog. However, in cattle, polydactyly is believed to be of multifactorial inheritance with no key mutation known at this time. While the heredity of polydactyly has also been explored in chickens and domestic pigs, little is known about the mode of inheritance and underlying molecular basis for polydactyly in horses.
A miniature Shetland Pony suspected of expressing polydactyly was brought into the local veterinary clinic for examination. Polydactyly was verified through computer tomography and DNA samples from the animal and its family were taken. Preliminary analyses of this family suggest that polydactyly has a recessive mode of inheritance. Through whole-genome re-sequencing of 5 individuals from this family (two affected and three suspected carriers) we aim to confirm this mode of inheritance for polydactyly and identify the causative locus. Sequencing is being performed by Illumina Hi-seq technology (PE 2+100 bp) with a resulting average depth of 10X for each individual. All reads will be aligned to the genome reference assembly using BWA and additional samples from polydactyly cases in other horse breeds are being collected to validate our results.