Further detailed studies revealed that the gene expression levels of human leukocyte antigen-A29.1, matrix metalloprotease 9, alanine aminopeptidase N, L-histidine decarboxylase, granulocyte colony-stimulating factor 3 receptor, and signal transducer and activator of transcription 3 were higher in CRPS patients than in healthy individuals (34). This evidence concerns the gene CSF3R and complex regional pain syndrome.