Loss of D13S25 locus
The D13S25 locus, which is in close proximity to the retinoblastoma gene (RB1) on chromosome band 13q14, lies close to a tumour suppressor locus whose inactivation contributes to the initiation or progression of low grade B-cell malignancy. Deletions affecting the interval between the RB1 gene and marker D13S25 at band 13q14 are the most frequent genetic abnormalities of B-cell chronic lymphocytic leukemia (B-CLL).
In almost 45% of CLL clones, deletions of a region telomeric to the RB1 gene (D13S25) are observed. Trisomy of 12 is the second most frequent chromosome aberration following 13q14 (RB1 and/or D13S25) deletions; followed by the del(11q), where the ATM (10%) gene is located and loss TP53 (7%) at 17p13.