A mutation in a gene called SCL24A4 that causes enamel hypoplasia, or poorly formed enamel of the teeth in Samoyed dogs has been identified by researchers at the Center for Companion Animal Health, University of California, Davis. The findings are published in the open access journal Canine Genetics and Epidemiology.
Affected dogs have discoloured and malformed teeth and the condition can lead to tooth loss, severe erosion and root infections. The researchers developed a test for the mutation that can enable breeders to eliminate the faulty gene in Samoyed through selective breeding.
Dr Niels Pedersen, lead author of the study said: "Fortunately, our research showed that this genetic disorder could be eliminated by breeders without any further loss of genetic diversity in the Samoyed breed. That is important information, because some attempts to eliminate deleterious genetic traits can actually result in loss of genetic diversity and greater inbreeding which could have other adverse health effects."
Dr Pedersen added: "Enamel hypoplasia in Samoyed is an autosomal recessive disease which means that two abnormal versions of a gene must be present in an individual for disease to develop. It also means that seemingly healthy individuals can carry an affected version of the gene and pass it on to their offspring."
The authors found that out of the 182 dogs whose genetic material was used in this study 14 dogs suffered from enamel hypoplasia. They all tested homozygous for the SCL24A4 gene mutation, which means they carried two affected genes. Twenty out of the remaining 168 healthy dogs tested heterozygous - they carried one affected version of the gene. The remaining 148 dogs did not carry the mutation.
The findings suggest that the SCL24A4 mutation has been present in the breed for several decades but may be increasing in frequency now because the faulty gene has been amplified due to inadvertent positive selection for a favourable physical trait encoded by genes in the same region of the genome. The authors also studied the existing genetic diversity in Samoyed from various parts of the world. Knowledge of breed-wide genetic diversity is important for decisions on how to best combat harmful genetic traits now and in the future.
Dr Pedersen said: "This is probably one of the first times that a newly recognized simple genetic trait - the SCL24A4 gene mutation - has been described in the context of the overall genetic background of a dog breed."
Dr Pedersen added: "Although previous research suggests that Samoyed are not in any immediate danger, genetic diversity may not be as great as presumed and that the current practice of random breeding must be sustained in order to reduce the chances of other deleterious mutations in the future.
The authors used gene samples from 182 Samoyed from North America (144), Europe (32) and Australia (6). Samples were sourced from breeders and owners using DNA sampling kits. The findings suggest that Samoyed from these distinct regions belong to a single breed with only small genetic differences caused by relative geographic isolation.
The authors found that even though all Samoyed descended from the same small set of founders, most dogs examined in this study were as unrelated as possible. One quarter of Samoyed dogs had a higher degree of parental relatedness, one quarter had a lower degree of relatedness, and half were random genetic representatives of the breed. Parental relatedness refers to how genetically similar an individual's parents' genes are to each other.
Seven out of 14 dogs affected by enamel hypoplasia and five healthy dogs were selected for genome wide association studies, which examines the entire set of genes in an individual to determine if any gene variant is associated with a trait - in this case the mutation in SCL24A4 was found to be associated with enamel hypoplasia. Work by one of the co-authors shows that the resulting health problems in affected Samoyed can be minimized by routine dental care.