A frequent form of hereditary episodic ataxia characterized by brief episodes of ataxia, neuromyotonia, and continuous interictal myokymia. The disease is episodic ataxia type 1 (MONDO_0008047). Also known as: EA1, Isaacs-Mertens syndrome, KCNA1 hereditary episodic ataxia, acetazolamide-responsive periodic ataxia, ataxia, episodic, with myokymia, continuous muscle fiber activity, episodic ataxia with myokymia, episodic ataxia, type 1.