Measurement of constitutive activity of BMP type I receptors

Bone morphogenetic proteins (BMPs) are pleiotropic cytokines controlling a multitude of processes, among which bone formation. BMPs function by binding and activating BMP type I and type II receptors, resulting in activation of Smad transcription factors and expression of BMP target genes. Mutations in the BMP type I receptor ALK2 were identified in patients suffering from Fibrodysplasia Ossificans Progressiva (FOP). The mutation found in all patients displaying classical FOP symptoms, the ALK2 R206H mutation, renders ALK2 constitutively active. Here, we provide a detailed description of how to determine whether other ALK2 mutations will confer constitutive activity to the receptor.