Cellular aging and mitochondrial aberrations may decrease MN performance below their functional threshold in adult SMA. SMN protein functions are mainly required during the development; indeed, also in healthy individuals the levels of SMN protein drop already after birth by 6.5-fold. SMN is also required in the adulthood but only at low levels, not significantly different between healthy and SMA individuals [12]. Many aging factors, such as decreased bioenergetics, increased ROS production and decreased axonal translation, may drop the function of NMJs just slightly below the threshold, ultimately causing SMA in adults. The figure was created with BioReneder.com.