Epilepsy and paroxysmal dyskinesia (PD) may sometimes be difficult to differentiate clinically. Although for this reason in the past it has been hypothesized that episodes of PD could represent a form of epilepsy (Lishman et al., 1962; Whitty et al., 1964; Burger et al., 1972), the current understanding is that the two disorders are distinct (Fahn, 1994).
However, there are several recent reports of families in which some individuals presented either or both paroxysmal disorders, with different age-related expression. Co-occurrence makes it likely that a common, genetically determined, pathophysiological abnormality is variably expressed in the cerebral cortex and in basal ganglia.
A rather homogeneous syndrome of autosomal dominant infantile convulsions and paroxysmal (dystonic) choreoathetosis (ICCA) was described in 20 families from France, China, Japan, and the United States (Szepetowski et al., 1997; Lee et al., 1998; Guerrini et al., 1999; Swoboda et al., 2000; Tomita et al., 1999). Linkage analysis allowed the mapping of the disease gene to partially overlapping loci in the pericentromeric region of chromosome 16.
Additional autosomal dominant pedigrees are on record, from Australia and Italy, in which epilepsy was variably associated with paroxysmal kinesigenic or exercise-induced dystonia (Perniola et al., 1998; Singh et al., 1999).
A pedigree in which three members in the same generation were affected by rolandic epilepsy, paroxysmal exercise-induced dystonia (PED) and writer's cramp was reported from Italy (Guerrini et al., 1999).