Some monogenic forms of JIA have been described, linked to variants in the genes encoding perforin (PRF1), Munc13-14 (UNC13D), syntaxin 11 (STX11), tumor necrosis factor-α-induced protein 3 (TNFAIP3) [5], laccase (multicopper reductase) domain-containing protein 1 (LACC1), and nuclear factor interleukin 3-regulated (NFIL3) [1], besides syndromic JIA conditions such as Blau syndrome (NOD2), Camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome (PRG4 and TRHR), multicentric carpotarsal osteolysis (MCTO) syndrome (MAFB) [2], and Majeed syndrome (LPIN2) [6]. This evidence concerns the gene STX11 and Down syndrome.