Alexander disease in Labrador Retrievers

Alexander's disease, or fibrinoid leukodystrophy, is a progressive fatal neurodegenerative disorder in which myelin formation is impaired and protein aggregates accumulate in astrocytes. Clinical signs are usually seen in dogs as young as twelve months of age and initially include impaired coordination, head tilt, nystagmus (oscillatory eye movements) and intolerance to touch. As the disease progresses, ataxia, muscle tone disturbances, progressively worsening tetraparesis (first, the paralysis of the hind limbs, and later, the paralysis of forelimbs), vestibular signs (unnatural head position, squinting) and myoclonic jerks at the head and the cervical region are encountered. Generalised muscular atrophy, rigidity, swallowing difficulties and changes in vocalisation can be observed. Gross pathological changes are not evident in all cases but may include diffuse atrophy of the brain and spinal cord and enlargement of the lateral ventricles.

In Labrador retrievers, the disease is caused by a missense mutation c.719G>A in the gene for the glial fibrillary acid protein (GFAP), a protein found in glial cells of the central nervous system.

Inheritance of the mutation is autosomal dominant. This means that one copy of the mutated gene inherited from one of the parents is enough to cause the symptoms of the disease. The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of puppies with this disease.

.

References:

Van Poucke, M., Martlé, V., Van Brantegem, L., Ducatelle, R., Van Ham, L., Bhatti, S., Peelman, L.J. : A canine orthologue of the human GFAP c.716G>A (p.Arg239His) variant causes Alexander disease in a Labrador retriever. Eur J Hum Genet 24:852-6, 2016. Pubmed reference: 26486469