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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 connective tissue disorder, with an autoimmune basis. The condition has features of 3 more common connective tissue diseases, hence its name.
The symptoms tend to occur in sequence over a number of years, so diagnosis can be difficult.
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 more 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.
Mixed connective tissue disease can be particularly severe in children, due to:
Dermatological manifestations of mixed connective tissue disease include:
Later stage complications of mixed connective tissue disease include nephritis, pericarditis and myocarditis, and interstitial lung disease.
The presence of high titres of auto-antibodies 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.
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