SP1 and supranuclear palsy, progressive, 1: A comparison of the use of early SD autoantibodies (SP1, anti-salivary protein; CA6, anti-carbonic anhydrase VI; PSP, anti-parotid secretory protein) vs classical autoantibodies (ANA, anti-Ro/La, RF) found that the early autoantibodies underperformed in comparison to the classical autoantibodies in differentiating sicca from juvenile SD (jSD) [36].