Several SLE-susceptibility loci are differentially-associated between adults and childhood-onset SLE patients; e.g. the functional PTPN22 R620W polymorphism is a risk factor to pediatric SLE patients from Mexico [16]; however, in this same population, this variant is not associated with adult SLE (identified by two GWAS and three candidate gene studies) [9,14,15,17,18]. Here, PTPN22 is linked to systemic lupus erythematosus.