Recommendation for Miniature Schnauzer Breeders and Owners: Importance of Genetic Testing for MAC

Miniature Schnauzers are one of the most beloved dog breeds, known for their energy, loyalty, and intelligence. While generally healthy, these dogs can have specific genetic predispositions that increase their risk for certain health conditions, such as sensitivity to Mycobacterium Avium Complex (MAC) infection. Though rare, this condition is fatal.

What is Mycobacterium Avium Complex (MAC)?

MAC is a group of Mycobacteria that traditionally includes three species: Mycobacterium avium, Mycobacterium intracellulare and Mycobacterium chimaera. They are nutoriously difficult to distinguish from one another by conventional microbiological techniques and cause the same spectrum of diseases. Members of MAC have the capacity to survive and thrive under many environmental conditions (low oxygen levels, low pH, extreme temperatures etc). This in combination with their ability to utilize many substances as nutrient sources enables them to grow in many different biotopes. After entering the oral cavity, these mycobacteria bind to gastrointestinal mucosa and after passing through the mechanical barriers, are recognized by mononuclear macrophages. The macropages relese cytokines and chemokines that further activate the host immune response and chemotaxis of immune cells. Dogs posses natural resistance to MAC infections since they are often exposed to them in the environment, but presence of the disease is often associated with immunodeficiency and genetic predispositions. In the case of Miniature Schnauzers, MAC susceptibility is attributed to a recessively inherited deletion in CARD9 adaptive protein (Mizukami, Dorsey-Oresto et al., 2024). All known Miniature Schnauzers which are homozygous for the  CARD9 mutant allele develop MAC infections. Additionaly, some studies suggest that MAC-infected Miniature Schnauzers have a propensity for fungal infections. Primary signs of MAC infections are lymph node, spleen and liver enlargement. Clinical signs of MAC infections include generalized weakness, lethargy, high fever, vomiting, diarrhea, weight loss and even anorexia. Some dogs may also develope conjunctivitis, present with blood in the stool and show respiratory problems.

MAC is a devastating condition that has no cure. Since MACs are zoonoses, aka they can infect both humans and animals, infected dogs pose a danger to young, old and immunocompromised owners.

Why is genetic testing crucial?

Since MAC sensitivity in Miniature Schnauzers is linked to an deletion in CARD9 gene, genetic testing should be performed to determine if your dog(s) carry this genetic variant. This mutation is inherited in an autosomal recessive manner, meaning a puppy must inherit a copy of the mutated gene from both parents to develop sensitivity.

Who should consider testing?

Genetic testing for MAC is recommended for:

     - Breeders: To identify dog(s) that carry the genetic variant for MAC and avoid breeding pairs that will potentially produce affected puppies

     - Miniature Schnauzer owners: Especially those planning to breed their dog or who want a deeper understanding of their dog’s genetic health.

What if a dog is a carrier of the MAC gene?

If genetic testing reveals your dog is a carrier of the mutation, it does not mean they will develop the condition. Carriers can live healthy lives, but breeders must carefully plan pairings to prevent producing affected puppies. If breeding two dogs which are carriers of MAC susceptibility allele, each puppy has a 25% chance of being affected by this devastating condition.

Conclusion: Prevention is key

Mycobacterium Avium Complex (MAC) can significantly affect the health of Miniature Schnauzers, but genetic testing allows breeders and owners to take a proactive approach to this issue. By testing and making informed decisions, you can ensure a healthier future for your dog and the breed as a whole.

Literature:

Kaczmarkowska, Aa, Didkowska, A., Kwiecień, E., Stefańska, I., Rzewuska, M., Anusz, K. (2022). The Mycobacterium avium complex - an underestimated threat to humans and animals. Annals of Agricultural and Environmental Medicine, 29(1), 22-27.

Kontos, V., Papadogiannakis, E. I., Mantziaras, G., Styliara, M., Kanavaki, S., A. (2014). Case of Disseminated Mycobacterium avium Infection in a Dog in Greece. Case Reports in Veterinary Medicine, 1-3,3.

Mizukami, K., Dorsey-Oresto, A., Raj, K., Eringis, A., Furrow, E., Martin, E., Yamanaka, D., Kehl, A., Kolicheski, A., Jagannathan, V., Leeb, T., Lionakis, M. S., Giger, U. (2024). Increased susceptibility to Mycobacterium avium complex infection in miniature Schnauzer dogs caused by a codon deletion in CARD9. Scientific Reports, 14(1), 10346.