What are the features of the episodic ataxias?
These autosomal dominant conditions include attacks of acute recurrent ataxia that can be treatable. In type 1 (EA1), patients have brief (1- to 2-minute) episodes of ataxia triggered by exercise, emotionality, or startle and interictally have myokymia of the face or hand muscles.
EA1 is caused by mutations in a voltage-gated potassium channel ( KCNA1 ). Episodic ataxia type 2 (EA2) consists of longer attacks (hours to days) triggered by stress, exercise, phenytoin, and caffeine.
Interictal nystagmus may be present. EA2 is caused by mutations in the calcium channel alpha 1 subunit ( CACN1A4 ), the same gene responsible for familial hemiplegic migraine and SCA6.
Slowly progressive ataxia, dysarthria, and vermian atrophy may occur.
Response to acetazolamide is quite dramatic in EA2, less so in EA1.