Neuroaxonal Dystrophy Spanish Water Dog Type (NAD)
Neuroaxonal Dystrophy Spanish Water Dog Type (NAD) is a neurodegenerative disorder affecting Spanish Water Dog. In general, neuroaxonal dystrophies represent a group of heterogeneous inherited neurodegenerative diseases. Differend forms of NAD share characteristic pathologic feature, but they vary in the clinical and the neurological signs, the progression of the disease and lesion distribution among but also within species. Except as a result of inherited genes, NAD-like findings were also associated with aging and toxic to metabolism conditions. They have been recognized in several species, such as dogs, cats, horses, sheeps and humans. Neuroaxonal dystrophy affected dogs breeds except Spanish Water Dog are Rottweiler, German Shepherd, Jack Russell Terrier, Collie Sheepdog, Papillon and Chihuahua.
In numerous neurodegenerative disorders, including Huntington’s, Alzheimer’s, Parkinson’s disease etc., impairment of authophagy is considered as a main mechanism of these disorders’ development. Autophagosomes sequestrate damages organelles and long-lived proteins and further degradation and subsequent release of amino acids and other molecules into the cytoplasm. Autophagy is essential for the metabolic homeostasis of neurons.
Characteristcs and symptoms
First clinical signs in affected Spanish Water Dogs appear between six and eleven months of age. Mild head tild, generalized mild cerebellar ataxia with hypermetria of the thoracic limbs and absent to decreased patellar reflex is present. Symptoms recognized by owners are gait abnormalities, incontinence alone, incontrolled defecation and behavioral changes, such as dullness, nervousness, and vocalization. Other signs affected dogs exhibit are compulsory pacing varying in its severity, proprioceptive deficits, decreased menace, visual deficits, inovoluntary eye movement (nystagmus) and decrease in muscle tone.
Pathomorphological findings are restricted to the central nervous system. Brain examination revealed neuronal loss and swollen axons, spheroids.
Newborn affected pups usually exhibit acute respiratory distress, stereotypical positioning of limbs, scoliosis, arthrogryposis (multiple joint contractures), pulmonary hypoplasia (incomplete development of the lungs) and respiratory failure.
Diagnosing Neuroaxonal Dystrophy takes in consideration differential diagnosis, which includes cerebellar hypoplasia, abiotrophy, hypomyelogenesis, and inflammatory or infectious disease (viral, rickettsia, protozoal, fungal, or immune-mediated).
Due to severity of the disorder and its progressive nature, it is often required to euthaniye affected dog due to humane reasons.
Neuroaxonal Dystrophy Spanish Water Dog Type (NAD) is caused by mutation in the TECPR2 gene. Immunohistochemistry and the ultrastructural findings showed that this gene involves in regulation of autophagosom accumulation in the autophagic pathways.
The disorder is inherited as an autosomal recessive disorder. Healthy parents of affected puppy are obligate heterozygotes, and therefore carry one mutant allele. Heterozygotes have no symptoms. Dogs homozygous for the mutation will display the symptoms of the Neuroaxonal Dystrophy Spanish Water Dog Type (NAD). At conception, when mating two carrier dogs, each cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
Hahn K, Rohdin C, Jagannathan V, Wohlsein P, Baumgärtner W, Seehusen F, et al. (2015): TECPR2 Associated Neuroaxonal Dystrophy in Spanish Water Dogs. PloS ONE 10 (11): e0141824. doi:10.1371/journal.pone.0141824
Diaz, J. V., et al. (2007.): Neuroaxonal Dystrophy in Dogs: Case Report in 2 Litters of Papillon Puppies. J Vet Intern Med 2007;21:531–534.