Spinocerebellar ataxia 6
Overview
Spinocerebellar ataxia type 6 (SCA6) is a rare, late-onset, autosomal dominant disorder, which, like other types of SCA, is characterized by dysarthria, oculomotor disorders, incontinence, peripheral neuropathy, and ataxia of gait, stance and the limbs due to cerebellar dysfunction. Unlike other types, SCA 6 is not fatal. This cerebellar function is permanent and progressive, differentiating it from episodic ataxia type 2 (EA2) where said dysfunction is episodic. In some SCA6 families, some members show these classic signs of SCA6 while others show signs more similar to EA2, suggesting that there is some phenotypic overlap between the two disorders. SCA6 is cased by mutations in CACNA1A, a gene encoding a calcium channel α subunit. These mutations tend to be trinucleotide repeats of CAG leading to stretches of glutamine greater than 19 and these mutant proteins form intracellular aggregations. Like many other polyglutamine expansion disorders, patients with longer expansions present with disease symptoms at an earlier age
Symptoms
SCA6 is typified by progressive and permanent cerebellar dysfunction. These cerebellar signs include ataxia and dysarthria, likely caused by cerebellar atrophy. Prior to diagnosis and the onset of major symptoms, patients often report a feeling of "wooziness" and momentary imbalance when turning corners or making rapid movements. The age at which symptoms first occur varies widely, from age 19 to 71, but is typically between 43 and 52. Other major signs of SCA6 are the loss of vibratory and proprioceptive sensation and nystagmus.[1] While most patients present with these severe progressive symptoms, others, sometimes within the same family, display episodic non-progressive symptoms more similar to episodic ataxia. Still others present with symptoms common to both SCA6 and familial hemiplegic migraine
Prognosis
There is currently no cure for SCA 6; however, there are supportive treatments that may be useful in managing symptoms.
Treatment
Treatment of manifestations: acetazolamide to eliminate episodes of ataxia; vestibular suppressants to reduce vertigo; clonopin for REM sleep disorders; home modifications for safety and convenience; canes and walkers to prevent falling; speech therapy and communication devices for dysarthria; weighted eating utensils and dressing hooks; feeding assessment when dysphagia becomes troublesome; CPAP for sleep apnea. Surveillance: annual or semiannual evaluation by a neurologist. Agents/circumstances to avoid:sedative-hypnotics (ethanol or certain medications) that increase incoordination. Other: Tremor-controlling drugs are not usually effective in reducing cerebellar tremors.