Autoantibody testing revealed antinuclear antibody (ANA) positivity (+++, 1:1000, centromere pattern), ANA blot positive for CENP-B, anti-Sm antibody positivity, and anti-U1-RNP antibody positivity, establishing a diagnosis of systemic sclerosis-mixed connective tissue disease. Here, RNPC3 is linked to systemic sclerosis.