UC Davis School of Veterinary Medicine Veterinary Genetics Laboratory

Autosomal Recessive Amelogenesis Imperfecta(ARAI) or Familial Enamel Hypoplasia of Samoyeds

Introduction

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.

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The Veterinary Genetics Laboratory offers a test for FEH to assist owners and breeders in identifying affected and carrier dogs. The test uses DNA collected from buccal (cheek) swabs. Breeders can use results from the test as a tool for selection of mating pairs to avoid producing affected dogs (Table 1).

Table 1.  Expected genetic outcome in puppies produced by mating females or males that do not carry the mutation (N/N), that carry one abnormal gene (N/FEH) or that are affected with FEH (FEH/FEH)

Female

Male

N/N

N/FEH

FEH/FEH

N/N

100% N/N

50% N/N, 50% N/FEH

100% N/FEH

N/FEH

50% N/N, 50% N/FEH

25% N/N, 50% N/FEH, 25% FEH/FEH

50% N/FEH, 50% FEH/FEH

FEH/FEH

100% N/FEH

50% N/FEH, 50%FEH/FEH

100%FEH/FEH

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Results reported as:

N/N: no copies of FEH mutation; dog is normal
N/FEH: 1 copy of FEH mutation; dog is normal but is a carrier
FEH/FEH: 2 copies of FEH mutation; dog is affected.

More Information

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 to occur. 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 mutation in the Italian Greyhound occurs in a gene called Enamelin (ENAM) and the defect has been published in the Journal of Animal Genetics in 2013: http://onlinelibrary.wiley.com/doi/10.1111/age.12043/abstract. The disease in Italian Greyhound is less severe than in Samoyed. The autosomal recessive mutation in Samoyed responsible for FEH has been confirmed, but has yet to be published. 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.

Fig. 1. Normal dentition in a Samoyed

Fig. 2. Samoyed with lesions of FEH showing irregular, worn, discolored and pitted tooth surfaces due to loss of enamel.

Fig. 3. Affected Samoyed with heavy tartar, gingivitis and staining of exposed dentin. Fig. 4. Same dog as in Figure 3 after deposits on the teeth were cleaned, irregular surfaces smoothed, and dentin sealed with resin.

 

 

 
Veterinary Genetics Laboratory, Tel 530-752-2211, Email VGL