One particularly frequent mutation, present in 50% of RCDII patients and 68% of EATL cases complicating RCDII, is the JAK1 p.G1097 [53], a hotspot mutation localized in a highly conserved position at the site of interaction of the JAK-1 negative regulator, a suppressor of cytokine signaling (SOCS)-1 [54]. The gene discussed is JAK1; the disease is enteropathy-associated T-cell lymphoma.