MARK2 and Peutz-Jeghers syndrome: The gene of liver kinase B1 (LKB1), encoding an approximately 50 kDa serine/threonine kinase, was first found mutated in Peutz-Jeghers Syndrome (PJS), which is a rare hereditary disease and is characterized by mucocutaneous pigmentation, increased risk of gastrointestinal hamartomatous polyposis as well as benign and malignant tumors [1,2,3,4].