The brain disease, known as cerebellar ataxia, leads to progressive loss of brain matter in the dog's cerebellum, the region of the brain responsible for control of the body's movements and some cognitive functions. As this brain region degenerates, motor coordination during walking, speech, gaze and balance goes. If the dog has the gene, symptoms of this degenerative disease start showing up around 2 months of age. There are no treatments, and the dogs are put down shortly thereafter.
'The identified ataxia gene is the first early-onset degenerative cerebellar ataxia gene that has been identified in dogs,' study researcher Hannes Lohi, of the University of Helsinki in Finland, said in a statement. 'The SEL1L gene has not been previously connected to cerebellar ataxias in any species, and it represents a novel candidate gene for human early-onset ataxias.'
By analyzing the genomes of Finnish hounds with and without cerebellar ataxia, researchers identified a mutation in the SEL1L gene that seemed to be the cause. It had no previous link to the disease.
The mutation changes an evolutionarily important part of the gene, which probably disrupts the normal function of the protein; this protein functions in a part of the cell called the endoplasmic reticulum, a structure in cells that makes sure proteins are mutation-free, packaged correctly and sent to the right place in the body to do their jobs.
If this protein-packaging process fails, the cell gets stressed out, and eventually dies. The researchers were able to measure this stress in the brains of mice with the mutated gene, who also get this brain disease. Their brain cells seem to be especially sensitive to this kind of stress and are the first to die, even though the SEL1L gene is expressed in many other tissues.
With information about this gene mutation, the researchers worked with the Finnish DNA-based animal diagnostics company Genoscoper to develop a genetic test to help eradicate the gene from the population. Breeding pairs of Finnish hounds could be screened to determine the likelihood that their offspring would have the disease before they were paired up.
The mutation is recessive, so the dog needs to have two copies of the mutation to have the disease. About 10 percent of Finnish hounds are carriers of this mutation, meaning they have one copy of the genetic mutation.
The gene may also play a role in human degenerative brain diseases. About 20 genes have been discovered that cause different types of ataxias in humans, but none explained this dog disease. The researchers are currently looking at human samples to determine if this SEL1L mutation could be at fault in any human cerebellar ataxias.
The study was detailed online June 14 the journal PLoS Genetics.
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