Complement 3 Deficiency

Other Names: C3 deficiency, Complement component 3 deficiency
Affected Genes: C3
Inheritance: Autosomal Recessive
Mutation: chr20:53573746 (canFam3): 1 bp deletion (del C)
Breed(s): Brittany

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Common Symptoms

Complement 3 deficiency is a disorder of the immune system affecting the Brittany that is characterized by a lack of the protein complement component 3. Complement component 3 (C3) plays an important role in preventing bacterial infection. C3 deficiency most commonly affects younger dogs and affected dogs will present with reoccurring bacterial infections, including pneumonia, urinary tract infections and uterine infections. C3 deficiency predisposes affected dogs to kidney disease early in life which can lead to chronic kidney failure and death.

Testing Tips

Genetic testing of the C3 gene will reliably determine whether a dog is a genetic Carrier of complement 3 deficiency. Complement 3 deficiency is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the C3 gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Dogs that are not carriers of the mutation have no increased risk of having affected pups.

There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.


  • Ameratunga R, Winkelstein JA, Brody L, Binns M, Cork LC, Colombani P, Valle D. Molecular analysis of the third component of canine complement (C3) and identification of the mutation responsible for hereditary canine C3 deficiency. Journal of Immunology. 1998; 160: 2824-2830. [not in PubMed]
  • Cork LC, Morris JM, Olson JL, Krakowka S, Swift AJ, Winkelstein JA. Membranoproliferative glomerulonephritis in dogs with a genetically determined deficiency of the third component of complement. Clin Immunol Immunopathol. 1991 Sep; 60(3):455-70. [PubMed: 1864020]
  • Johnson JP, McLean RH, Cork LC, Winkelstein JA. Genetic analysis of an inherited deficiency of the third component of complement in Brittany spaniel dogs. Am J Med Genet. 1986 Nov; 25(3):557-62. [PubMed: 3789016]