Drug-induced dyskinesia and cognitive changes in people with Parkinson's disease who have the 22q11.2 deletion might be related to the underlying pathogenic mechanism (eg, perhaps related to a change in catechol-O-methyltransferase [COMT] concentration secondary to loss of one copy of the COMT gene located within the chromosome 22q11.2 region). Here, COMT is linked to Parkinson disease.