Ribonucleoproteins (RNP) is composed of RNA and protein and is localised in the cell nucleus. The RNA components are described as U1 to U6 depending on their chromatographic behaviour. Apart from the individual RNA component, each U-n(nuclear)RNP particle displays six various core proteins (B, B', D, E, F, G). Antibodies against RNP in high titer and clinical symptom are use to diagnose Sharp syndrome (mixed connective tissue disease, MCTD). This syndrome is a multi-symptomatic and multiform mixed connective tissue disease combining symptoms of rheumatoid arthritis, SLE, systemic sclerosis, CREST syndrome and vasculitides.