Escayg et al. (2000) found a cys104-to-phe (C104F) missense mutation in affected members of a German family with generalized epilepsy (EIG9; 607682) and praxis-induced seizures, and in a French Canadian family with episodic ataxia type 5 (EA5; 613855). The German family had affected father and son; the French Canadian family had 5 affected individuals in 3 generations. In the German family, the affected father and son presented with an atypical but similar clinical syndrome of idiopathic generalized epilepsy with rare juvenile atypical prolonged absences and occasional generalized tonic-clonic seizures (GTCS). The proband had normal intellectual and psychomotor development. One febrile convulsion occurred at age 3 years. After age 6, he had occasional GTCS, predominantly on awakening, and, after age 12, occasional episodes of absence were described. A prolonged atypical absence occurred in the eldest son at age 14 years, while he was playing cards. At age 17, he experienced GTCS shortly after awakening. Two years later, he experienced a generalized tonic seizure while playing a complex strategic game after sleep withdrawal. He experienced occasional prolonged staring spells when lacking sleep. Both affected individuals reported that seizures were precipitated by playing complex strategic games (praxis induction), suggesting an unusual cognitive trigger of seizure initiation (Inoue et al., 1992). In the French Canadian family with the C104F mutation, the proband, after age 20 years, experienced recurrent episodes of vertigo and ataxia that lasted for several hours. Interictal examination showed spontaneous downbeat and gaze-evoked nystagmus and mild dysarthria and truncal ataxia. The proband's mother had identical episodes of vertigo and ataxia after age 30 years as well as longstanding dysarthria and imbalance. Acetazolamide prevented the attacks in both the proband and the mother, and the attacks recurred when acetazolamide was briefly discontinued.
