Paroxysmal Kinesigenic Dyskinesia in Twins With Chromosome 16p11.2 Duplication Syndrome

Paroxysmal kinesigenic dyskinesia (PKD) (MIM# 128200) is a movement disorder characterized by brief episodes of involuntary movements consisting of dystonia, chorea, or myoclonus, usually triggered by sudden voluntary movements.1 Pathogenic variants in PRRT2 (MIM# 614386), located on chromosome 16p11.2, have been identified as the most common cause of PKD.2 Most of the reported patients (approximately 80%) had the frameshift pathogenic variant c.649dupC (p. Arg217Profs*8), which causes a premature stop codon. Other reported variants are nonsense, frameshift, or rarely missense that are predicted to cause a truncated protein, absence of protein product through nonsense-mediated mRNA decay, or nonfunctional protein.3 Isolated PKD is typically associated with heterozygous intragenic variants in PRRT2 . Symptomatic PKD has been reported in 6 patients with 16p11.2 microdeletion syndrome (MIM# 611913).4 PKD is thus postulated to result from PRRT2 haploinsufficiency. The reciprocal chromosome 16p11.2 duplication syndrome (MIM# 614671) is associated with autism, ADHD, developmental delay, intellectual disability, epilepsy, hypotonia, congenital anomalies, and microcephaly5,6 but has not until now been associated with PKD.