Congenital Methemoglobinemia
Affected Genes: CYB5R3
Inheritance: Autosomal Recessive
Variant(canFam6):
chr10:22772479: A>C
Breed: Aussiedoodle
Bernedoodle
Bordoodle
Cavapoo
Cavapoochon
Cockapoo
Goldendoodle
Irishdoodle
Maltipoo
Miniature Poodle
Pomeranian
Pomsky
Poodle
Schnoodle
Sheepadoodle
Toy Poodle
Yorkiepoo
General Information: Congenital methemoglobinemia is an inherited blood disorder in dogs that impairs oxygen delivery to body tissues. Affected dogs usually do not require veterinary intervention but may experience lifelong exercise intolerance. They often display a blue or purple hue to their gums, tongue, and skin, which becomes more pronounced during exercise. Despite these symptoms, many dogs lead relatively normal lives.
How to Read Your Dog's Test Results for this Genetic Variant:
Two Variants Detected: Dog Likely Affected
One Variant Detected: Dog Unlikely Affected
No Variants Detected: No Effect
Gene / Testing Information:Genetic testing of the CYB5R3 gene can determine if a dog is a carrier of congenital methemoglobinemia, an autosomal recessive disorder that requires two copies of the mutated gene for the disease to manifest. Carrier dogs generally do not exhibit symptoms but breeding two carriers together can produce affected pups, with each pup having a 25% chance of inheriting the disease and a 50% chance of being a carrier. Reliable genetic testing is crucial for making informed breeding decisions to prevent affected litters. To eliminate the mutation from breeding lines, it is advised not to breed known carriers together. Dogs without the mutation do not have an increased risk of producing affected pups.
References:
Shino H, Otsuka-Yamasaki Y, Sato T, Ooi K, Inanami O, Sato R, Yamasaki M. Familial Congenital Methemoglobinemia in Pomeranian Dogs Caused by a Missense Variant in the NADH-Cytochrome B5 Reductase Gene. J Vet Intern Med. 2018 32(1):165-171.
Zhou S, Tearle R, Jozani RJ, Winra B, Schaaf O, Nicholson A, Peaston A. Genetic cause for congenital methemoglobinemia in an Australian Pomeranian dog. J Vet Intern Med. 2019 33(2):868-873.