ATM and B-cell chronic lymphocytic leukemia: The frequency of ATM mutations in large series of CLL patients it is not so well understood, mostly owing to the fact that its size and the scattered distribution of its somatic mutations precludes the drafting of an amplicon-limited design.33, 34 We found ATM to be the most frequently mutated gene, with a predominance of clonal variants, indicating the ancestral-founding nature of these lesions.