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What are the features of the episodic ataxias?
Genetic and clinical summary of episodic ataxia (EA)
| Type | OMIM | Inheritance | Genes | Protein | Age of onset | Attack duration | Associated symptoms | Interictal findings |
|---|---|---|---|---|---|---|---|---|
| EA1 | 160120 | AD | KCNA1 (12p13) | Potassium channel (Kv1.1) | 2-15 | Seconds-min | Vertigo, dysarthria, weakness, tremor, seizure | Myokymia |
| EA2 | 108500 | AD | CACNA1A (19p13) | P/Q type calcium channel | 2-20 | Hours | Vertigo, dysarthria, diplopia, weakness, tonic upward gaze, headache, seizure, dystonia, cognitive impairment | Nystagmus, ataxia |
| α1 subunit (Cav2.1) | ||||||||
| EA3 | 606554 | AD | Unknown | Unknown | 1-42 | 1 min to 6 h | Vertigo, diplopia, weakness, tinnitus, headache, visual blurring | Myokymia |
| EA4 | 606552 | AD | Unknown | Unknown | 23-60 | Brief | Vertigo, diplopia | Nystagmus, abnormal smooth pursuit |
| EA5 | 613855 | AD | CACNB4 (2q22-23) | P/Q type calcium channel | > 20 | Hours | Vertigo, dysarthria | Nystagmus, ataxia |
| β4 subunit | ||||||||
| EA6 | 612656 | AD or sporadic | SLC1A3 (5p13.2) | Excitatory amino acid transporter 1 | 5-14 | Hours-days | Vertigo, weakness, seizure | Nystagmus, ataxia |
| EA7 | 611907 | Multiple | Unknown | Unknown | < 20 | Hours-days | Vertigo, dysarthria, weakness | No |
| EA8 | 616055 | AD | UBR4 (1p36.13) | Ubiquitin-protein ligase | Early infancy | Min to 24 h | Vertigo, weakness | Nystagmus, ataxia myokymia |
OMIM: Oline Mendelian Inheritance of Man, AD: autosomal dominant.
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.
References
Choi KD, Choi JH. Episodic Ataxias: Clinical and Genetic Features. J Mov Disord. 2016 Sep;9(3):129-35. doi: 10.14802/jmd.16028. Epub 2016 Sep 21. PMID: 27667184; PMCID: PMC5035943. https://pmc.ncbi.nlm.nih.gov/articles/PMC5035943/
