Autosomal recessive amelogenesis imperfecta (ARAI), also known as familial enamel hypoplasia (FEH), is an inherited genetic disorder of tooth enamel that occurs in Samoyeds.
Phenotype: Familial enamel hypoplasia (FEH) is characterized by enamel pitting and tooth discoloration. FEH in Samoyeds is usually noticed when the permanent teeth erupt, around 5-6 months of age. The deciduous teeth appear normal. The disorder is characterized by marked thinning or absence of the outer enamel layer with irregular pitting, which predisposes the dog to patchy tooth discoloration, dentin sensitivity, premature tooth wear, dental caries, pulp exposure, tartar accumulation, gingivitis, and periodontitis. Periodontal disease can lead to bone loss, gum recession, and tooth loss. Halitosis (foul-smelling breath) is a common effect of the dental disease.
Mode of Inheritance: Autosomal recessive
Alleles: N = Normal, FEH = Familial enamel hypoplasia
Breeds appropriate for testing: Samoyed
Explanation of Results:
Dogs with N/N genotype will not have familial enamel hypoplasia and cannot transmit this variant to their offspring.
Dogs with N/FEH genotype will not be affected by familial enamel hypoplasia, but are carriers. They will transmit this variant to 50% of their offspring. Matings between two carriers are predicted to produce 25% familial enamel hypoplasia-affected puppies.
Dogs with FEH/FEH genotype will have familial enamel hypoplasia and will transmit this variant to all of their offspring.
Autosomal recessive amelogenesis imperfecta (ARAI) is an inherited genetic disorder of tooth enamel that occurs in humans. It is commonly known as familial enamel hypoplasia (FEH) in dogs. Dr. Niels Pedersen and his research group at the School of Veterinary Medicine, University of California, Davis have researched FEH in several breeds and have identified breed-specific mutations in two breeds, the Italian Greyhound and the Samoyed. Mutations in other breeds have yet to be identified.
The common occurrence of FEH in pure breeds of dogs and ARAI in humans is related to the complexity of tooth formation. The formation of enamel is the last step in tooth development and involves the activity of many genes and their proteins acting at the same or different times in pre- and post-natal life. The involvement of many genes increases the likelihood of a deleterious mutation occurring. These mutations are inadvertently subjected to positive selection in association (linkage) with traits that are deemed desirable, frequently from a popular sire.
Amelogenesis imperfecta in humans can be autosomal dominant or recessive, or sex-linked. The mutation can be associated only with the teeth (non-syndromic) or can involve several structures in the body (syndromic). FEH in dogs appears to be predominantly non-syndromic, autosomal recessive in inheritance, and the causative mutation unique to each breed. The autosomal recessive mutation in Samoyed responsible for FEH has been confirmed. An analogous mutation has been associated with a specific form of ARAI in humans. Based on preliminary testing, it is estimated that 1-2% of Samoyed are affected with FEH and over 10% of dogs with normal-appearing teeth are carriers.
FEH in Samoyed is usually noticed when the permanent teeth erupt, around 5-6 months of age. The deciduous teeth appear normal. The disorder is characterized by marked thinning or absence of the outer enamel layer with irregular pitting, which predisposes to patchy tooth discoloration, dentin sensitivity, premature tooth wear, dental caries, pulp exposure, tartar accumulation, gingivitis, and periodontitis. Periodontal disease can lead to bone loss, gum recession, and tooth loss. Halitosis is a common sequela of the dental disease.
Figure 1 shows a Samoyed with normal teeth. Figures 2 and 3 show typical Samoyed with FEH, and figure 4 shows the results of restorative and cosmetic dentistry.
Testing for FEH assists owners and breeders in identifying affected and carrier dogs. Breeders can use results from the test as a tool for selection of mating pairs to avoid producing affected dogs.
1 copy of FEH mutation. Dog is normal but is a carrier.
2 copies of FEH mutation. Dog is affected.
Pedersen, N.C., Shope, B., & Liu, H. (2017). An autosomal recessive mutation in SCL24A4 causing enamel hypoplasia in Samoyed and its relationship to breed-wide genetic diversity. Canine Genetics Epidemiology,4, 11. doi: 10.1186/s40575-017-0049-1