PTEN missense mutation that results in the substitution of serine at position 170 with arginine affects the phosphatase domain of PTEN. Serine residue S170 is involved in the formation of intedomain hydrogen bonds between the phosphatase domain and the membrane-binding C2 domain (Lee et al. 1999). PTEN S170R (Ser170Arg) mutant shows markedly decreased phosphoinositide phosphatase activity (Han et al. 2000). PTEN S170R is found as a germline mutation in Bannayan-Riley-Ruvalcaba familial cancer syndrome (Marsh et al. 1997).