| SCA1 is an autosomal dominant ataxia, with mid life onset characterized by motor symptoms, dementia, dysphagia (swallowing difficulty), and chorea (involuntary spasmodic movements). Pathologically, symptoms are caused by a loss of Purkinje cells in the cerebellar cortex. With the use of technology, in 1993 researchers discovered that SCA1 was due to an unstable CAG trinucleotide repeat encoding for polyglutamine. Since the finding of SCA1 researchers have made discoveries about the biology of this disease, finding that protein folding and degradation of the ataxin-1 protein is a focus for future research into the disease. |
| SCA2 is an autosomal dominant cerebellar ataxia characterized by symptoms that can mimic parkinsonism, involving gait dysfunction, rigidity, slowness, and sometimes resting tremor. Often SCA2 is noticeable through a reduction in saccade velocity (speed of moving eyes side to side). Dementia may also be present as a symptom. SCA2 expansions can lead to a wide range of phenotypes from typical PD to PSP. Again this spinocerebellar ataxia is caused by CAG repeat expansions. The protein of SCA2 is ataxin2, still of unknown function. |
| SCA3: SCA3 is also known as Machado-Joseph disease. First described in 1972 by Nakano et al as a form of dominantly inherited ataxia occurring in William Machado descendants from the Portuguese Azores islands. SCA3 is characterized by gait disturbance, retinal degeneration, dementia, and some patients present with REM sleep disorder and/or psychiatric illness. There is no reduction in saccade velocity for SCA3. SCA3 is also caused by a CAG repeat expansion. SCA3 may present as idiopathic parkinson's disease in some cases, and has been shown to be the presentation of SCA3 in African populations. |
| SCA6: SCA6 is in the subgroup-channelopathy meaning the SCA6 protein function involves a calcium channel. Symptoms have been shown to be relatively pure ataxia presentation with later onset (>55 years). Typically the clinical picture is mildy progressive ataxia of limbs and gait, dysarthria, and some sensory loss. |
| SCA7: Features include ataxia and retinal degeneration, may also include torticollis, dystonia, and dementia. Age of onset is extremely variable, and much anticipation is shown within families. In some cases, an early sign of the disease was a slowing of the saccades. |
| SCA12: Autosomal dominant, typically beginning with tremor in the fourth decade and progressing to ataxia. Parkinsonism signs include rigidity and bradykinesia and often dementia. Activation tremor is present and may be the most common sign. The tremor resembles essential tremor and many patients were given this diagnosis initially. Dementia in older patients and some that exhibit psychiatric disorders including anxiety and depression (Holmes et al). Age onset varies 8-55 years. As the disease progresses, patients may develop mild cerebellar dysfunction including gait ataxia and limb and eye movement abnormalities. |
| SCA17: In some pedigrees disease seems to be transmitted dominantly and in another pedigrees it seems to be recessive. Clinical features include presenting in the third decade to include gait ataxia and dementia, progressing over several decades to include bradykinesia (slowness) and paucity of movement. Parkinsonism in these cases mainly showed bradykinesia, gait disturbance, and postural reflex disturbance with tremor and rigidity being less prominent. Age onset ranged between 19-48 years. |
