MEN1 and gastrin-producing neuroendocrine tumor: However, nonsense mutations (Tyr312Stop and Arg460Stop) have been detected (Olufemi et al., 1998) in MEN1 families with the Burin or prolactinoma variant (Agarwal et al., 1997) which is characterized by a high occurrence of prolactinomas and a low occurrence of gastrinomas (Hao et al., 2004; Olufemi et al., 1998).