U1 and systemic sclerosis: Other less frequently detected ANA in SSc react with different intracellular targets such as ribonuclear proteins (anti-U1 RNP, anti-U3 RNP/antifibrillarin, and anti-U11/U12 RNP autoantibodies) or nucleolar antigens [anti-Th/To, antinucleolar organizer region 90 (anti-NOR90), anti-Ku, and antipolymyositis/Scl (PM/Scl) autoantibodies] [1–3].