A 15-year-old female is brought to the clinic by her parents due to dark spots on her lips and inside her mouth that have been present since childhood. Recently, she has experienced intermittent abdominal pain and rectal bleeding. Physical examination reveals dark brown macules on her lips, buccal mucosa, and fingertips. A colonoscopy identifies multiple polyps in the small intestine and colon. Genetic testing is performed to investigate the underlying cause. What is the most common genetic mutation associated with Peutz-Jeghers syndrome?
