Therefore, in this retrospective study, we evaluate two commercial fluoroenzymatic immunoassays (FEIA; EliATM U1-RNP and EliATM RNP70) for measuring anti-U1-RNP and anti-RNP70 antibodies in samples from four cohorts: SLE, MCTD, primary Sjögren’s syndrome (pSS) and healthy blood donors (HBDs). This evidence concerns the gene SNRNP70 and mixed connective tissue disease.