McCune-Albright syndrome

A 8-year-old boy is brought to the emergency room after a severe fall from a tree during a family vacation. His mother reports a history of recurrent fractures. Physical examination shows visible scoliosis and large areas of light brown hyperpigmentation with jagged borders on the right side of his back. Armpit hair and facial hair is also noted. His voice is noticeably deeper than most young boys his age. Which of the following gene mutations is most likely the cause of his condition?