Polioencephalopathy (PE)

Polioencephalopathy (PE) is a neurological disorder characterized by lesions in the grey matter of the brain. It occurs in humans and, more rarely, in animals, and is typically a consequence of metabolic disturbances such as malnutrition, toxicity, or congenital metabolic defects. This condition can lead to a wide range of neurological impairments. Because the clinical signs of PE can be very diverse, diagnosing the disease based on symptoms alone is challenging.

In a Eurasier family, a form of polioencephalopathy was linked to a genetic variant in the MECR gene. The affected puppies began to show movement disorder episodes between the ages of 2 and 6 months. These included generalized ataxia, a hypermetric gait (exaggerated limb movements), dystonia (muscle spasms), and uncontrolled flexion and extension movements of the forelimbs. The frequency and severity of these episodes increased over time. Additionally, there were indications that excitement, loud noises, or overstimulation may trigger the episodes.

As the disease progressed, further motoric impairments developed, including difficulties with walking and standing, muscle atrophy, and abnormal posture. Some dogs also showed divergent strabismus (eyes pointing outward). However, no impairments in consciousness or behaviour were observed.

The MECR gene encodes the mitochondrial enzyme trans-2-enoyl-CoA reductase, which plays a key role in lipoic acid synthesis. Lipoic acid is essential for mitochondrial fatty acid synthesis and energy metabolism. Variants in the MECR gene lead to neurodegenerative changes, particularly in energy-demanding tissues such as the basal ganglia in the brain and the optic nerve.