Anti-single-stranded DNA (ssDNA)
Antibodies to DNA can be divided into two groups:
1. Antibodies that bind only to native double-stranded DNA (dsDNA);
2. Antibodies binding to single-stranded DNA (ssDNA).
Antibodies to single-stranded DNA (anti-ssDNA) belong to the group of antinuclear antibodies. IgM class anti-ssDNAs have no independent diagnostic value when IgG class anti-ssDNAs are characteristic of many systemic connective tissue diseases such as systemic lupus erythematosus, rheumatoid arthritis, polymyositis/dermatomyositis, and others. Anti-ssDNAs are most commonly seen in patients with focal scleroderma.
Anti-ssDNA is detected in 50% of patients with different forms of focal scleroderma. Focal scleroderma is characterized by limited fibrosis of the skin and subcutaneous adipose tissue, but may occasionally involve muscle and bone tissue. Unlike systemic scleroderma, the prognosis of the disease is favorable, since with focal scleroderma, internal organs are never affected and the Raynaud's phenomenon is not observed. For the differential diagnosis of focal and systemic scleroderma, the concentration of anti-ssDNA can be examined. These antibodies are more characteristic of localized, focal scleroderma. A specific sign of systemic sclerosis is the presence of anti-Scl-70. It is important to note that the negative result of the anti-ssDNA analysis does not completely exclude the diagnosis of focal scleroderma.
The analysis of anti-ssDNA has the greatest diagnostic value in pediatric dermatology. The most common form of focal scleroderma in children is linear scleroderma (en coup de sabre). In this case, fibrosis occurs linearly along the length of the limb or along the course of a neurovascular bundle. With the development of deep atrophy with the involvement of muscle structures, the disease takes a disabling character. It is shown that in patients with the linear form of scleroderma, a high concentration of anti-ssDNA is associated with the involvement of the underlying muscle tissue, so the analysis of the concentration of these autoantibodies can be used to assess the prognosis of the disease.
The level of anti-ssDNA reflects the activity of focal scleroderma. The highest concentration of these autoantibodies is found in the generalized form of focal scleroderma. When remission of the disease is achieved, the concentration of antibodies decreases and the test result may become negative. For this reason, the analysis of the concentration of anti-ssDNA can be used to control the treatment of the disease.
It should be noted that the presence of anti-ssDNA is not a strictly specific sign of focal scleroderma. In addition, these autoantibodies can be detected in the blood of healthy individuals. For this reason, a positive test result does not always mean that a disease is present.
Also, antibodies to ssDNA can be detected in the serum of SLE patients in 87% of cases in the acute phase of the disease and in 43% in the remission phase. When taking a number of medicines, SLE syndrome may develop. For the differential diagnosis of drug-induced SLE syndrome, the level of antibodies to ssDNA is an important diagnostic criterion. In patients with drug-induced SLE syndrome, the level of antibodies to ssDNA is increased in more than 50% of cases.
In addition, elevated serum levels of antibodies to ssDNA have been found in patients with mononucleosis, hepatitis, and some forms of leukemia. The interpretation of the test is carried out taking into account additional clinical, laboratory, and instrumental data.