Germline mutations in LKB1 that lead to the development of PJS result in loss of function of LKB1 through truncations, deletions, or direct mutations to the kinase domain abolishing LKB1 kinase activity (Mehenni et al., 1998; Tiainen et al., 1999; Ylikorkala et al., 1999; Boudeau et al., 2003a). The gene discussed is STK11; the disease is Peutz-Jeghers syndrome.