According to the literature, the prevalence of Ro52 mono-positive patients with IP accompanied by CTDs is 50% among patients with mixed connective tissue disease (MCTD),(33) 80% among those with idiopathic inflammatory myopathies,(31) 57% or 36.2% among those with SSc,(32,34) and 5.6% among those with UCTD.(35) Healthy subjects were not positive for Ro52 in another study.(13) Based on these reports, the frequency of Ro52 mono-positivity seems to be lower among non-CTD patients with IP than among patients with established CTDs and IP, but higher than among patients with UCTD and IP. This evidence concerns the gene TRIM21 and systemic sclerosis.