SMN1 and proximal spinal muscular atrophy: Other aspects should be clarified before stating that SMN transcript analysis is a biomarker for SMA: (1) like in many other conditions, PBMCs are not target cells in SMA and it should be demonstrated that SMN levels in blood reflect those found in target tissues, i.e., the spinal cord but also skeletal muscle (to our knowledge, a single study on animal models is currently available [57]); (2) like SMN protein dosage, transcript analysis is not indicated for the evaluation of potential therapeutic compounds that do not modify SMN levels.