One complex CN variable locus is CCL3L1. Copy number variation at CCL3L1 has been associated with susceptibility to HIV infection (Liu et al., 2010), autoimmune disease (Burns et al., 2005; Mamtani et al., 2008; McKinney et al., 2008) and asthma (Lee et al., 2011). Here, CCL3L3 is linked to asthma.