A 40-year-old man is evaluated in the clinic for cognitive decline. The patient has a history of mild cognitive impairment, but he has been increasingly forgetful over the past few months. He previously enjoyed working at the community library but had to quit as he could no longer perform his duties. The patient is completely dependent on his caregiver for daily activities of living. He has recently been found lost on streets near his home on multiple occasions. Vitals are within normal limits. The patient is oriented to place and person only and is unable to cooperate with the remainder of the cognitive examination. Physical examination shows a single crease on palms, a gap between the first two toes and prominent epicanthal folds. Which of the following is the most likely cause of this patient's condition?
a. Elimination tool De novo mutation of MECP2 gene CGG trinucleotide repeat expansion
b. Silenced paternally derived UBE3A
c. Extra copy of amyloid precursor protein
d. Absence of hypoxanthine guanine phosphoribosyltransferase