MPL and essential thrombocythemia: Another atypical mutation of MPL was found only in a female ET patient, which caused thymidine to cytosine and cytosine to guanine substitution at nucleotides 1543 and 1546, respectively, and resulted in a Tryptophan to Arginine and a Glutamine to Glutamate substitution at codons 515 (W515R) and 516 (Q516E).