Progressive abnormal gait in an adult Jack Russell Terrier with a homozygous frameshift variant in SETX (senataxin).

SETX frameshift variant causes progressive gait abnormalities in Jack Russell Terriers.

This case report describes an 8-year-old Jack Russell Terrier presenting with progressive gait disturbances characterized by severe bilateral hyperflexion of all limbs, hypermetric movement, and ultimately a hopping gait in the pelvic limbs with compensatory tripedal locomotion. Over a 2-year progression, the dog developed generalized stiffness without ataxia. Diagnostic workup including complete blood count, serum biochemistry, creatine kinase activity, electrophysiological examination, and muscle biopsy were unremarkable. Genetic sequencing identified a homozygous frameshift variant in SETX (senataxin) predicted to truncate approximately 85% of the protein, establishing a novel genetic etiology for gait abnormalities in this breed. SETX encodes a DNA/RNA helicase involved in DNA damage response and transcription, and mutations have been associated with ataxia and motor neuron disease in humans. This case expands the genetic differential diagnosis for progressive gait disorders in Jack Russell Terriers and highlights the importance of genetic testing in breed-specific neurological presentations.

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