Mutations in human lymphocytes commonly involve gene duplication and resemble those seen in cancer cells

Mutations in human lymphocytes are commonly due to gene deletion. To investigate the mechanism of deletion for autosomal genes, we immunoselected lymphocytes mutated at the HLA-A locus and cloned them for molecular analysis. Of 36 mutant clones that showed deletion of the selected HLA-A allele, 8 had resulted from a simple gene deletion, whereas 28 had resulted from a more complex mutational event involving reduplication of the nonselected HLA-A allele as indicated by hybridization intensity on Southern blots. In 3 of the 28 clones, retention of heterozygosity at the HLA-B locus indicated that the reduplication was due to recombination between the two chromosomes 6; but in the remaining 25 clones, distinction could no be made between recombination and chromosome reduplication. The results indicate that mutations in normal somatic cells frequently result in hemizygosity or homozygosity at gene loci and, thereby, resemble the mutations thought to be important in the etiology of various forms of cancer.