Spinocerebellar ataxia (SCA) also referred to as hereditary ataxia is seen in the Parson Russell Terrier (PRT) or Jack Russell Terrier dog breed is a disease of progressive incoordination of gait and loss of balance.

Clinical signs usually become notable between 6 and 12 months of age with affected dogs presenting with symmetric spinocerebellar ataxia particularly evident in the pelvic limbs.

The degree of truncal ataxia, pelvic limb hypermetria and impaired balance is progressive, particularly during the initial months of disease.

A certain degree of stabilisation as well as intermittent worsening may occur.

At the later stages of the disease ambulation often becomes difficult, with owners often electing to euthanise affected dogs on welfare grounds.