Mutation of JAK2 is observed in several hematological disorders including ET [8,9,10,11], Polycythemia Vera [8,9,10,11], Primary Myelofibrosis [8,9,10,11] and Acute Lymphoid Leukemia (ALL) [25,26] as well as chromosomal translocations involving the fusion partners TEL [27,28,29], BCR [30], PCM1 [31,32,33], PAX5 [34], SEC 31A [35] and SSBP2 [36]. The gene discussed is PAX5; the disease is essential thrombocythemia.