Congenital methemoglobinemia (CYB5R3-related) - all breeds

What does this test analyse?

This genetic test analyses the CYB5R3 variant c.214G>A in all breeds. The condition is known as congenital methemoglobinemia, methemoglobinemia, NADH cytochrome b5 reductase deficiency and hereditary canine methaemoglobinaemia.

What does this mean for the dog?

Methemoglobinemia occurs when too much haemoglobin is converted to methemoglobin, reducing oxygen delivery to tissues. Dogs may show bluish mucous membranes, shortness of breath, exercise intolerance, coughing, increased heart rate and darker blood. CYB5R3 encodes cytochrome b5 reductase, an enzyme that normally converts methemoglobin back to functional haemoglobin.

Practical value of this test

• Breeders can distinguish clear dogs, carriers and genetically affected dogs before planning matings.
• The result helps avoid carrier x carrier matings and directly lowers the risk of puppies with this inherited disorder.
• Valuable carriers can remain in the population responsibly by combining them only with clear partners.
• In puppies or young dogs with matching signs, the test provides a concrete genetic explanation that supports rapid follow-up.
• The test helps separate an inherited cause from other causes with similar symptoms.

Inheritance and interpretation

The trait is autosomal recessive. G/G means the tested variant was not detected. G/A means carrier. A/A causes congenital methemoglobinemia and is reported as a genetically affected result.