Missense and truncation mutations in the ATM gene have been demonstrated in adult leukaemias: T-cell prolymphocytic leukaemia (T-PLL) (Stilgenbauer et al, 1997; Vorechovsky et al, 1997; Stoppa-Lyonnet et al, 1998; Yuille et al, 1998), and B-cell chronic lymphocytic leukaemia (B-CLL) (Bullrich et al, 1999; Schaffner et al, 1999; Stankovic et al, 1999; 2002). This evidence concerns the gene ATM and T-cell prolymphocytic leukemia.