[Undifferentiated, overlapping and mixed connective tissue diseases]. / Enfermedad mixta del tejido conjuntivo, conectivopatía indiferenciada y síndromes de superposición.

Mixed connective tissue disease (MCTD), undifferentiated connective tissue disease and overlap syndromes are autoimmune systemic diseases that must be differentiated. Antibodies against the U1-ribonucleoprotein complex --spliceosome-- allows the diagnosis of mixed connective tissue disease. Links between the immunologic and clinical phenomena are emerging. Longitudinal studies of patients with MCTD highlight the impact of pulmonary hypertension and contribute to define the disease. Immunogenetic studies hold MCTD as an independent disease.