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At a glance

Spinocerebellar ataxia represents a group of slow and progressive neurodegenerative diseases of varying inherited degrees of rarity, which is in contrast to a related group of neurological disorders that are acquired following traumatic injuries or other external agents. The development of ataxia is a neurologic sign that may provide a clue to the nature of the underlying disorder. Interruption of afferent and efferent connections within the spinocerebellar system results in ataxic gait, scanning dysarthria, explosive speech, intention tremor, dysdiadochokinesia, dysmetria, and abnormalities of eye movements. Many variations are encountered in the clinical phenotype, ranging from findings of pure cerebellar dysfunction to mixed patterns of involvement reflecting extrapyramidal, brain stem, and cerebral cortical involvement. Previously, all autosomal dominant ataxias were called Marie ataxia and all autosomal recessive ataxias were called Friedreich ataxia. They may be present at almost any time between infancy and adulthood.

Synonyms

SCA Syndrome; Spinocerebellar ataxia; ADCA Syndrome.

Classification

This classification is based on the pattern of inheritance or mode of transmission (ie, autosomal dominant, autosomal recessive, and X-linked).

  • Autosomal Dominant Cerebellar Ataxia (ADCA) Syndromes: Heterogeneous group of disorders in which progressive cerebellar ataxia is the primary feature. The autosomal dominant ataxias are, however, most often referred to as the spinocerebellar ataxias, identified as SCA1 through SCA45. (See Table S-2).

  • ADCA Type I (Spinocerebellar Ataxia 1 (SCA1); SCA2; SCA3;Machado-Joseph Disease): Clinically characterized by cerebellar ataxia of gait and limbs, invariably associated with supranuclear ophthalmoplegia, pyramidal or extrapyramidal signs, mild dementia, and peripheral neuropathy.

  • ADCA Type II: Medical condition presenting similar features of ACDA Type I but characterized by the addition of macular and retinal degeneration

  • ADCA Type III: A pure form of late-onset cerebellar ataxia.

Some ataxias are called “Episodic Ataxias”. There is a very rare disorder known as “Dentalo-Rubro-Pallido-Luysian Atrophy (DRPLA)” which is also considered in the classification. Table S-2 reports the autosomal dominant hereditary ataxias and each type is indicated as SCA#.

  • Autosomal Recessive Hereditary Ataxias: There are fewer autosomal recessive ataxias than autosomal dominant hereditary ataxias. The autosomal recessive hereditary ataxias are grouped according to their clinical presentation:

    • Pure cerebellar Syndrome: ARCA2 Syndrome; ☞Marinesco-Sjögren Syndrome (MSS)

    • Spinocerebellar and Posterior Cord Syndrome with sensory polyneuropathy: ☞Friedreich Ataxia; ☞Marinesco-Sjögren Syndrome (MSS)

    • Cerebellar Syndrome and Sensitivo-Motor Polyneuropathy: ☞Louis-Bar Syndrome (Ataxia Telangiectasia); ☞Andermann Syndrome (Charlevoix-Saguenay Spastic Ataxia; ARSACS Syndrome)

  • X-Linked Ataxias: This is a very rare group and few patients have been diagnosed with this medical condition.

History

Early attempts to classify inherited ataxias were based on anatomic localization of pathologic changes (eg, spinocerebellar, pure cerebellar ataxias). The classification of hereditary ataxias is, however, complex and several schools of thought vying for recognition.

Incidence

5 to 6/100,000.

Genetic inheritance

The molecular ...

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