What is the definition or description of: mixed connective tissue disease?

Overlap syndrome : This is an overlap syndrome with manifestations that can include those of rheumatoid arthritis systemic lupus, scleroderma, and polymyositis. Different patients will have different combination of these components, over the long term it appears that many can get scleroderma like findings. Two or more components can occur. It has a variety of specific laboratory studies especially the RNP blood test