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Author: Dr Susannah Fraser, MBChB, FRCP (Edin), Consultant Dermatologist, NHS Fife, Scotland, United Kingdom; Chief Editor: A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, February 2016.
Mixed connective tissue disease is a rare autoimmune connective tissue disorder with anti-U1RNP auto-antibodies and clinical features of three commoner connective tissue diseases:
Mixed connective tissue disease is also known as Sharp syndrome.
The cause of mixed connective tissue disease is not fully known. Due to the presence of autoantibodies, it is classified is an autoimmune disease.
It is most common in patients with HLA-DR4, suggesting it has a genetic background.
The course of mixed connective tissue disease may be similar to systemic lupus erythematosus, or systemic sclerosis. However the clinical features tend to evolve in sequence over a number of years, making diagnosis difficult sometimes.
Mixed connective tissue disease can be particularly severe in children, due to:
Dermatological manifestations of mixed connective tissue disease include:
Cutaneous signs of mixed connective tissue disease
Late stage complications of mixed connective tissue disease include nephritis, pericarditis and myocarditis, and interstitial lung disease.
Babies of mothers with mixed connective tissue disease and anti-U1RNP autoantibodies can develop neonatal lupus erythematosus and a rare non-lethal form of chondrodysplasia punctata.
The presence of high titres of autoantibodies against the U1-ribonucleoprotein (RNP) complex is a defining feature of mixed connective tissue disease. This was previously termed an antibody to ‘extractable nuclear antigens’ (anti-ENA). The U1 small nuclear ribonucleoprotein particle is a target of autoreactive B cells and T cells.
Treatment may depend on the relative severity of lupus-like, systemic sclerosis-like and polymyositis-like aspects of mixed connective tissue disease. These can include:
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