SIRT1 and systemic sclerosis: On the bases of this scientific background, the objective of the present study was to measure, for the first time, circulating SIRT1 and SIRT3 levels by enzyme-linked immune-sorbent assay (ELISA) in a well-characterized cohort of SSc patients, focusing on their possible association with disease clinical subsets and features, and their potential as biomarkers reflecting SSc activity and severity.