None of the remaining control individuals, including patients suffering from systemic sclerosis (n = 26), polymyositis/dermatomyositis (n = 13), MCTD (n = 26), Sjögren's syndrome (n = 24), or infectious diseases (n = 77), exhibited reactivity to the SmD3 peptide. This evidence concerns the gene SNRPD3 and mixed connective tissue disease.