Circular layout depicting the associations of selected IGHV and IGHD genes in MCL. The Circos software package (http://mkweb.bcgsc.ca/circos) was used to explore the combinations of the 4 predominant IGHV genes with the 10 more frequent IGHD genes. Strong biases are evident, as exemplified by the restricted pairing of IGHV3-21/IGHD3-3, IGHV1-8/IGHD3-10, and IGHV4-34 with IGHD2-2 and IGHD2-15.