Review Question - QID 212723

A 9-year-old boy is brought to the clinic by his parents to establish care. The family recently moved from Canada and would like to find a primary care physician to manage his various health concerns. The patient was diagnosed with autism spectrum disorder (ASD) at the age of 4 and has since been undergoing behavioral therapy with moderate success. However, the patient had his first seizure 1 year ago and has been having breakthrough seizures despite treatment with levetiracetam. The mother claims that he has “calcium in his brain” based on past computed tomography scans of the head. A physical examination demonstrates a timid boy with poor interaction and an unremarkable physical exam. A skin finding is present on the lower back and is shown in Figure A. What mutation is responsible for causing this patient’s symptoms?