Human defensin gene copy number polymorphisms: comprehensive analysis of independent variation in alpha- and beta-defensin regions at 8p22-p23.

To investigate defensin gene copy number polymorphisms, a quantitative real-time PCR assay was developed and used to study DNA from 27 unrelated individuals of diverse ethnic and racial backgrounds. The DEFB4 and DEFB103A genes varied in tandem, with copy numbers 2 to 8, with a mode of 6 per diploid genome (PDG). The combined copy numbers of the DEFA1 and DEFA3 genes ranged from 5 to 14, with a mode of 10 copies PDG. The copy numbers of the DEFA1/3 genes varied independently of those of the DEFB4 and DEFB103A genes. The amount of HNP-1 and HNP-3 peptides expressed in neutrophils was found to be proportional to the combined copy number of DEFA1 and DEFA3. The DEFA3 allele was absent in 7/27 subjects. The highly copy-number-variable DEFA1 and DEFA3 genes are flanked by other defensin genes present uniformly at 2 copies PDG. The remarkable variability in defensin gene copy numbers could contribute to differences in individual resistance to infections.