Perspectives on familial chronic lymphocytic leukemia: genes and the environment.

Chronic lymphocytic leukemia (CLL) comprises a substantial proportion of leukemias in adults in the western hemisphere. Male gender, increasing age, ethnicity (high in Caucasians, lowest in Asians), and family history are risk factors. Although no specific extrinsic etiologic factors have been established, farming and pesticide exposure are associated with increased risk. Migration studies confirm that ethnic groups retain the risk associated with their origin rather than their new location, favoring a role for heredity. Kindreds with multiple cases of CLL have been well described in the literature and studies in large populations confirm that lymphoproliferative malignancies and especially CLL occur together at a rate that cannot be attributed to chance. Since environmental factors cannot readily explain the familial aggregations, a hereditary factor that affects susceptibility to CLL is likely. The identification of clones that are immunophenotypically identical to CLL in healthy individuals from CLL kindreds (14% to 18%) as well as in the general population (3.5% in age bracket >65 years) suggests a possible precursor condition, but longitudinal studies will be necessary to establish significance in the general population. Family (linkage) and population (candidate gene) studies to date have been too small to identify the specific genes that account for increased susceptibility; larger studies including planned consortia to identify additional high-risk kindreds for genetic studies, as well as the application of advanced technologies such as genomics, cytogenetic, expression, and proteomics, are widely expected to advance understanding over the next few years.