In addition, methylation alterations in CLL, such as ZAP70 [13] and HOXA4 [14], have been proposed as prognostic biomarker, and differential methylation profiles are used to classify CLL patients in three molecular CLL subtypes having different clinical features and deriving from B-cell subpopulations at different stages of differentiation [5,15,16]. The gene discussed is ZAP70; the disease is B-cell chronic lymphocytic leukemia.