Clinical and linkage data in 11 families with paroxysmal kynesigenic dyskinesia (PKD), with or without infantile convulsions (IC), were studied at the University of Utah, Salt Lake City, and multiple international centers. These families of diverse ethnic backgound had 95 affected individuals, the majority having chromosome 16 as the major locus, with heterogeneity. Kinesigenic dyskinesia (PKD) occurred in 42, infantile convulsions (IC) in 37, and a combined phenotype in 16. Infantile convulsions were usually afebrile and developed between 3 and 18 months; they remitted by age 3 years without treatment. Episodes of PKD began at 6 to 23 years (average 11 years), and were triggered by sudden movement, stress, and anxiety; they were controlled by anticonvulsant drugs, and were less frequent after age 25 years. EEGs were generally normal. The PKD/IC syndrome spans the phenotypic spectrum between epilepsy and movement disorder. 
COMMENT. In an editorial, Berkovic SF classifies the Paroxysmal kinesigenic dyskinesia with infantile convulsions as a “channelopathy.” . Other paroxysmal disorders implicating channelopathies and manifested by seizures and dyskinesias include febrile seizures (sodium channel mutations), benign familial neonatal convulsions (potassium channel mutations), and episodic ataxia type 2 (calcium channel mutations). Different mutations are responsible for the diverse phenotypes. With PKD/IC syndrome, a single mutation may cause age-dependent symptoms: convulsions in infancy and dyskinesia in adolescence.
Risperidone and withdrawal dyskinesia is reported in a 13-year-old boy with ADHD, conduct disorder, and psychotic features, treated with lithium, valproic acid, and risperidone . Two weeks after the resperidone was discontinued, a withdrawal dyskinesia manifested with mouth movements, neck twisting, and intermittent upward gaze. Although withdrawal dyskinesia may resolve within 6 weeks, the author raises concerns about the use of resperidone in ADHD children with ODD and CD, but without psychosis.