U3-RNP antibodies target the U3 small nucleolar ribonucleoprotein (U3-RNP) complex, which consists of the protein fibrillarin and U3 RNA. These antibodies are found in about 4% to 10% of patients with SSc, and are especially common in African American SSc patients (approximately 30%). U3-RNP antibodies are rarely found in patients with other autoimmune disorders; thus, the presence of these antibodies supports a SSc diagnosis.
These antibodies occur most often in dcSSc, but they can also occur in lcSSc.
U3-RNP antibodies are associated with multiorgan involvement, including the heart, kidneys, muscle, lungs, and gastrointestinal system. Their presence is an independent risk factor for the development of PAH, and PAH is the most common cause of death in U3-RNP–positive patients. Therefore, their presence indicates a poorer prognosis.
References:
Stochmal A, Czuwara J, Trojanowska M, et al. Antinuclear antibodies in systemic sclerosis: an update. Clin Rev Allergy Immunol. 2020;58(1):40-51. doi:10.1007/s12016-018-8718-8
Hamaguchi Y, Takehara K. Anti-nuclear autoantibodies in systemic sclerosis: news and perspectives. J Scleroderma Relat Disord. 2018;3(3):201-213. doi:10.1177/2397198318783930
Kayser C, Fritzler MJ. Autoantibodies in systemic sclerosis: unanswered questions. Front Immunol. 2015;6:167. doi:10.3389/fimmu.2015.00167
Fibrillarin
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