Neonatal ataxia in Coton de Tulear

Ataxia is a neurological symptom consisting of a lack of normal coordination of movements. In case of neonatal ataxia the lack of normal coordination becomes evident soon after birth.

Neonatal ataxia was (BNAt – Bandera´s neonatal ataxia) originally called Bandera´s syndrome after the first puppy of Coton de Tulear breed affected, in which the clinical signs of this disease were described.

All affected pups showed similar clinical signs. They nursed well and grew adequately, but have difficulties from the time they became active. The affected pups are unable to stand and walk. Despite all their efforts, they move uncoordinatedly all four limbs and these movements are often compared with “swimmer” movements. When attempting to move, they will frequently push themselves forward, but fall immediately to one side or the other in an attempt to get up. After the fall they often continue to paddle by their limbs.

Another common sign is a tremor or bobbing of the head that are most dramatic when the pup is trying hardest to hold the head steady, for example, when the pup is trying to eat or sniff an object and is referred to as an intention tremor. There may also be a tremor or jerking of the eyes.

The study by Zeng et al. 2011 has described the insertion of retrotransposon in GRM1 gene that disrupts the GRM1 coding sequence in exon 8. Retrotransposons are sequences in the genome that can move or transpose themselves to new positions within the genome. For their „jumping“ in the genome they need RNA polymerases that can transcribe them into RNA. By reverse transcription, the copy of RNA is transcribed into DNA that can be inserted in the genome of the organism in a new position.

The GRM1-gene encodes metabotropic glutamate receptor (mGluR1) which belongs to the group of transmembrane receptors also called receptors coupled with G proteins. The ligand binding induces activation of signalling cascades mediated by G-protein.

In a 4-month old affected puppy, no macroscopic or microscopic abnormalities in the brain anatomy were identified. There were observed only minor ultrastructural abnormalities in the molecular layer of the cerebellum. In the affected pups, the important biochemical pathways are disrupted and therefore the dogs affected with BNAt are not able to walk normally.

Further study of dogs affected with BNAt may clarify the possible role of mGluR1 in learning and memory (Zeng et al. 2011).

Neonatal ataxia in Coton de Tulear is inherited as an autosomal recessive trait. That means the disease affects dogs with P/P (positive / positive) genotype only. The dogs with P/N (positive /negative) genotype are clinically without any symptom. They are genetically considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers). Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

References:
Zeng R. et al. ; A truncated retrotransposon disrupt the GRM1 coding sequence in Coton de Tulear Dogs with Bandera´s neonatal ataxia; J Vet Intern Med 2011