Germline loss-of-function mutations affecting the serine-threonine kinase 11 (STK11) gene (also called LKB1), located on chromosome 19p13.3, have been shown to cause PJS in 50% to 90% of cases; however, about 25% of PJS patients present de novo mutations [7,8]. This evidence concerns the gene STK11 and Peutz-Jeghers syndrome.