Review Question - QID 214635

A 14-year-old boy is brought to a psychiatrist with a 3-month history of increased aggression and personality changes. His parents say that until the beginning of this school year he was a well-behaved child who achieved good grades and had many friends. Since then, he has become increasingly withdrawn and has episodes such that he knocks over objects without warning. His parents became concerned when he started falling and having bursts of anger where he lashed out against his siblings. Physical exam reveals the finding shown in Figure A. Which of the following mechanisms is most likely responsible for pathologic accumulation of a toxic substance in this patient?