In the absence of Sm antibodies, which condition is characterized by certain autoantibodies?

Mixed connective tissue disease is characterized by the presence of specific autoantibodies, particularly anti-U1 RNP antibodies, which target the ribonucleoprotein complex. This condition often presents features that overlap with systemic lupus erythematosus, systemic sclerosis, and polymyositis, but the hallmark of mixed connective tissue disease is the unique combination of symptoms and the presence of anti-U1 RNP autoantibodies without the presence of Sm antibodies.

In the context of the question, it's important to highlight that, although systemic lupus erythematosus (SLE) is a well-known autoimmune condition associated with various autoantibodies including Sm antibodies, the presence of Sm antibodies would rule out mixed connective tissue disease. Therefore, the absence of Sm antibodies suggests that another autoimmune condition must be considered, and mixed connective tissue disease fits that requirement due to its distinct autoantibody profile and symptomatology.

The other choices, while also associated with certain autoantibodies, have different specificities and do not align with the premise of the question regarding the absence of Sm antibodies. For example, systemic lupus erythematosus typically has Sm antibodies as a common marker of disease, and systemic sclerosis and rheumatoid arthritis have their own specific