 Before the discovery of the RAMPs and the identification of heteromeric receptors for the calcitonin family of peptides, a single G Protein coupled Adrenomedullin receptor was identified, but more recent reports have cast doubts as to its importance in the major effects of adrenomedullin.In more recent research, the roles of the AM1 and AM2 receptors have been clarified through studies in genetically manipulated mice.The adrenomedullin knockout is an embryonic lethal phenotype and dies mid gestation from a condition known as hydrops fetalis.