Miniature Schnauzer Health Panel

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Progressive retinal atrophies (PRA) are a group of inherited eye disorders that result in vision loss. Multiple forms of PRA have been described in dogs in association with different genetic variants. We currently offer a genetic test for a type referred to as HIVEP3/PPT1-PRA. Two genetic variants are associated with this disorder, one in HIVEP3 and one in PPT1. Our test screens for the variant in HIVEP3. We do not offer testing for the PPT1 variant because it is more difficult to perform and obtain accurate results. Note that a previous name for HIVEP3/PPT1-PRA was Type B PRA. 

Who gets HIVEP3/PPT1-PRA and what is the cause?

HIVEP3/PPT1-PRA was discovered in Miniature Schnauzers. It is currently reported to be the most common form of PRA in the breed. There isn’t enough information yet to confidently determine whether the HIVEP3 or PPT1 variant causes PRA risk. However, both of the variants are associated with PRA and are typically, but not always, inherited together. Because the PPT1 variant is difficult to accurately test for, the current recommendation is to use the HIVEP3 variant for testing. A limitation of this test is that it is possible that a dog might test clear or carrier for the HIVEP3 variant but have two copies of the PPT1 and thus be at risk for developing PRA. It is also possible for dogs that test clear or carrier to develop PRA or other eye disorders from other causes. 

At this time, we do not offer HIVEP3/PPT1-PRA testing for breeds other than the Miniature Schnauzer. 

What are the clinical signs of HIVEP3/PPT1-PRA?

Dogs with HIVEP3/PPT1-PRA have progressive vision loss. As puppies, vision and eye exams are normal. By 3-5 years of age, affected dogs have vision loss and evidence of severe retinal disease on eye exam (e.g., loss or attenuation of retinal vessels, hyperreflectivity, retinal thinning, and loss of photoreceptor cells). Dogs eventually become blind. 

There is no cure for HIVEP3/PPT1-PRA. However, once diagnosed, there are management strategies that might help. For example, avoid making major changes to your dog’s environment and use safety gates to prevent your dog from falling down stairs or entering dangerous areas (e.g., pools). Consider ways to use sounds to alert your pet, such as new verbal commands (e.g., “step down”) or bells on other household pets. Also be careful about safety outside of the home. Have your dog wear a leash when outside and consider a label for their collar or harness that says “blind dog” to make other people aware and avoid startling them.

Persistent Müllerian Duct Syndrome (PMDS) is a reproductive disorder in which the uterus and other parts of the female reproductive tract develop in male dogs. An important consequence of this disease is cryptorchidism (undescended testicles), which occurs in ~50% of affected dogs and causes infertility, as well as increased risk for testicular tumors. The external genitalia can be otherwise normal, making it easy to overlook PMDS as the underlying cause of cryptorchidism.  We believe that the mutation is relatively common in this breed (~25% carrier rate, ~2% genetically affected). Female dogs are not affected by this disease, but can pass the mutation on to their offspring.

Note: Cryptorchidism has many potential causes, of which PMDS is only one.

Myotonia Congenita (MC) is a recessively inherited disorder affecting skeletal muscles resulting from a genetic variant in CLCN1, a gene that encodes a channel that is important for muscle relaxation. Dogs affected by MC may have enlarged (hypertrophic) muscles and an uncoordinated, "bunny-hopping" and/or stiff gait with delayed muscle relaxation after exercise. Dental and jaw abnormalities may be noted, as well as noisy breathing, difficulty swallowing, and excessive salivation. Cold and excitement may exacerbate clinical signs.