TRIM21 and polymyositis: Anti-Ku was originally described in Japanese patients with SSc/PM overlap, but in the North American population it appears to be present in a more SLE-like disease [22] The anti-Ku positive patients had higher anti-Ro-52 values than the majority of the other SSc antibody groups (figure 1) but when an expanded number of non-SSc anti-Ku positive sera were analysed there was no significant difference in anti-Ro-52 levels to the SSc population (with the exception of the anti-aats and anti-Ro-60 groups).