Differential Levels of mRNAs in Normal B Lymphocytes, Monoclonal B Lymphocytosis and Chronic Lymphocytic Leukemia Cells from the Same Family Identify Susceptibility Genes

INTRODUCTION People with a family history of chronic lymphocytic leukemia (F-CLL) have an increased risk of monoclonal B lymphocytosis (F-MBL), which is found in up to 18% of first-degree relatives of patients compared to 5% of the total population. This may indicate that the presence of an F-MBL in the relative of a F-CLL patient is due to genetic susceptibility. In this study, we hypothesized that progressive changes in gene expression result in malignant transformation of B lymphocytes to F-MBL, and subsequent alterations in gene expression occur before overt F-CLL develops. The aim of this study of affected and unaffected individuals from a family with multiple CLL cases was to compare mRNA expression levels in control B-lymphocytes, pre-malignant F-MBL and malignant F-CLL cells. METHODS To identify inherited changes in gene expression, a high-resolution DNA microarray was used to identify differentially abundant mRNAs in age-matched cases of F-MBL (n = 4), F-CLL (n = 2) and unaffected family relatives (F-Controls, n = 3) within one family. These were then compared to non-kindred controls (NK-Controls, n = 3) and sporadic CLL (S-CLL) cases (n = 6). RESULTS Seven differentially abundant mRNAs were identified against similar genetic backgrounds of the family: GRASP and AC016745.3 were decreased in F-MBL and further decreased in F-CLL compared to F-Controls, whereas C11orf80 and METTL8 were progressively increased. PARP3 was increased in F-MBL compared to F-Controls but was decreased in F-CLL compared to F-MBL. Compared to F-Controls, levels of ROR1 and LEF1 were similarly increased in F-MBL and F-CLL. For six of the genes, there were no differences in mRNA levels between S-CLL and F-CLL; however PARP3 was higher in S-CLL. CONCLUSION These results are consistent with the hypothesis that changes in expression of specific genes contribute to transformation from normal lymphocytes to MBL and CLL.