RET and multiple endocrine neoplasia type 2A: Activating RET mutations, which cause constitutively active signaling, result in pediatric cancer syndromes such as multiple endocrine neoplasia (MEN) type 2A and 2B46,47 but except for the rare occasions (total of five patients in three distinct kindreds48–50 of MEN2A), the majority of MEN patients display normal kidney morphology.