The lymphocyte-specific protein tyrosine kinase (LCK) belongs to the Src family of non-receptor tyrosine kinases.18,19 LCK plays an essential role in natural killer (NK)-cell and T-cell signalling, in which LCK inhibition has shown potential for the therapeutic treatment of leukaemia and autoimmune diseases, such as rheumatoid arthritis.20–23 More recently, LCK has been identified as an important regulator of neuronal morphology and memory functions.24 However, the involvement of LCK activity in these critical processes within the central nervous system remains poorly understood. This evidence concerns the gene LCK and rheumatoid arthritis.