THBS4 and proximal spinal muscular atrophy: Based on the functional role of TSP4 at synapses [35] including NMJs [36], its potential to serve as a disease relevant biomarker in SMA—even enabling patient stratification in terms of distinguishing between clinically non-affected and affected patients as well as type 1 therapy responders versus type 2 and 3 responders—is underlined by its pathophysiological meaning.