LOA (Late Onset Ataxia) in Russell Terrier

The Late Onset Ataxia (LOA) in the Russell Terriers is a genetic disease characterized by lack of balance and incoordination of gait. The visual symptoms are usually noticed between 6 months and 12 months of age.  The first symptoms are stiffness of hind limbs, difficulty going up the stairs and incoordination when jumping. The disease is progressive and the condition of the affected dogs is getting worse and the typical signs include stiff jumping and "dancing" in place.  In the worst stage of the disease, the dogs often fall down and have trouble getting up and walking. The disease is progressive and after the onset of the first signs the problems with balance and gait incoordination are increasing rapidly. In some cases, possible stabilisation of the condition was described, but in the most cases the progression of the disease is unbearable and the affected dogs are often prematurely euthanized.

The neurological examination of the affected dogs shows symmetric spino-cerebellar ataxia - cerebellar malfunction characterized by inability to carry out precise and quick movements of skeletal muscles.

So far there have been described the neonatal cerebellar ataxia in Coton de Tulear dogs (GRM1 gene), cerebellar ataxia in Finnish Hounds (SEL1L gene) and cerebellar abiotrophy in Beagles (SPTBN2 gene).

The mutation responsible for the Late Onset Ataxia in Russel Terriers was found and described in 2013 (Forman at al, 2013). The mutation causes a substitution c.344G>A  in CAPN1 gene leading to cytosine replacement by tyrosine (C155Y).

Mutation that causes LOA in Russell Terriers 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).

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References:

Forman OP, De Risio L, Mellersh CS (2013) Missense Mutation in CAPN1 Is Associated with Spinocerebellar Ataxia in the Parson Russell Terrier Dog  Breed. PLoS ONE 8(5): e64627. doi:10.1371/journal.pone.0064627