Late Onset Ataxia (LOA)
Late Onset Ataxia is a hereditary disease characterized mostly by a progressive incoordination of walking. Late onset ataxia is reffered to also as spinocerebellar ataxia (SCA) or hereditary ataxia. It is caused by a genetic mutation. Until today two different forms of spinocerebellar ataxia have been described in Jack Russel Terriers and Parson Russel Terriers and the researches suspect there are also other forms of ataxia in these breeds as well. In the Parson Russell Terrier breed a mutation in CAPN1 has been identified and associated with the spinocerebellar ataxia.
Characteristics and Symptoms
Late onset ataxia is progressive, with first symptoms occuring usually between 6 months and 1 year of age. The dog owners first start to notice that dog is incoordinated or is having difficulties in climbing stairs or jumping. How the disease progresses, dog is having troubles in standing, and starts to fall frequently, with difficulties while returning into standing position. Other clinical signs of ataxia are difficulty in climbing and jumping, are hypermetria and impaired balance. Histopathological examination showed abnormalities of the entire central nervous system: bilateral symmetrical myelopathy, axonopathy combined with myelin loss and swelling of axons. Recent research reported also changes in the brainstem and brain involvement. Due to severe symptoms and progressive nature of this disorder, affected dogs are often euthanized.
Late onset ataxia is caused by a missense mutation in the CAPN1. Though the exact frequency in the overall Parson Russell Terrier population is unknown, 33% out of 205 clinically healthy Parson Russell Terriers tested were carriers of the mutation. LOA is inherited in an autosomal recessive pattern. Healthy parents of an affected dogs are obligate heterozygotes, and therefore carry one mutant allele. Heterozygotes have no symptoms. At conception, 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.
There is no cure for LOA, and only way to prevent it, is to breed dogs which are not carriers of the mutation. Defected genes for autosomal recessive disease can be passed for many generations without affected individuals occurring until two carriers are bred to one another. The only way to find out if there is a chance of getting an affected puppy is to do genetic testing.