Classification of the FHL subtypes.PRF1 mutations were initially classified in the 57 patients who fulfilled the diagnostic criteria of FHL. When perforin expression was positive or a PRF1 mutation was absent, the samples were analyzed for a MUNC13-4 mutations. The results allowed the FHL patients to be classified into 3 subtypes: FHL2 (n = 11), FHL3 (n = 8), and non-FHL2/FHL3 (n = 16).