U1 and systemic sclerosis: In addition to those SSc-specific antibodies (SSc-SA), a wide range of SSc-associated antibodies have also been reported over the last decades: Anti-U1 RNP, anti-PM–Scl [16,17,18,19], anti-Ku [20], anti- Ro52/tripartite motif (TRIM) 21, and anti-human upstream binding factor (hUBF)/anti-NOR-90 antibodies [21].