Although the −1661 is less characterized than other SNPs in the CTLA-4 gene [34], it has been associated with increased risk of multiple sclerosis [35], type 1 diabetes mellitus [36, 37] systemic sclerosis [38], oral squamous cell carcinoma [39], and lymph node involvement in breast cancer [40]. This evidence concerns the gene CTLA4 and systemic sclerosis.