Subsequent studies demonstrated that blood MNC of juvenile idiopathic arthritis (JIA) patients are characterized by a marked over-expression of p75NTR and sortilin, the proNGF high affinity receptor complex and a significant decrease of TrkA expression, while healthy donor blood MNC show a high TrkA and a low p75NTR expression (21). This evidence concerns the gene NTRK1 and juvenile idiopathic arthritis.