Episodic ataxia type 1(EA1)
What is EA1?
EA1 is a disease that is mainly characterized by muscle stiffness and twitching. EA1 also creates incoordination and balance problems.
EA1 is a potassium channelopathy characterized by constant myokymia and dramatic episodes of spastic contractions of the skeletal muscles of the head, arms, and legs with loss of both motor coordination and balance. During attacks some individuals may experience vertigo, blurred vision, diplopia, nausea, headache, diaphoresis, clumsiness, stiffening of the body, dysarthric speech, and difficulty in breathing. Onset is in childhood or early adolescence. Other findings can include delayed motor development, cognitive disability, choreoathetosis, and carpal spasm. Diagnosis/testing. Diagnosis is based on clinical findings and molecular genetic testing of KCNA1, the only gene known to be associated with EA1.
EA1 is an autosomal dominant disease. Most individuals with a diagnosis of EA1 have an affected parent. Offspring of affected individuals have a 50% chance of inheriting the disease-causing gene mutation. Prenatal testing is available for pregnancies at increased risk for EA1 if the mutation has been identified in the family.
Treatment of manifestations: Acetazolamide (ACTZ), a carbonic-anhydrase (CA) inhibitor, may reduce the frequency and severity of the attacks in some but not all affected individuals. Antiepileptic drugs (AEDs) may significantly reduce the frequency of the attacks in some individuals.
Episodic ataxia type 2 (EA2)
What is EA2?
EA2 is a disease that is mainly characterized by involuntary jerky eye movements.
During EA2 attacks, dysarthria, diplopia, tinnitus, dystonia, hemiplegia, and headache can occur. About 50% of individuals with EA2 have migraine headaches. Onset is typically in childhood or early adolescence (age range 2-32 years). Frequency of attacks can range from once or twice a year to three or four times a week. Attacks can be triggered by stress, exertion, caffeine, alcohol, and phenytoin and can be stopped or decreased in frequency and severity by administration of acetazolamide. Between attacks, individuals may initially be asymptomatic but eventually develop interictal findings that can include nystagmus and ataxia.
EA2 is an autosomal dominant disease. Most individuals with a diagnosis of EA2 have an affected parent. The proportion of cases caused by de novo gene mutations is unknown. Offspring of affected individuals have a 50% chance of inheriting the disease-causing gene mutation. Prenatal testing is available for pregnancies at increased risk for EA2 if the mutation has been identified in the family.
Treatment of manifestations is Acetazolamide. It is effective in controlling or reducing the frequency and severity of attacks; although generally well tolerated, the most common side effects are paresthesia of the extremities, rash, and renal calculi; acetazolamide does not appear to prevent the progression of interictal symptoms.