 Deficiencies in homologous recombination have been strongly linked to cancer formation in humans . For example , each of the cancer @-@ related diseases Bloom 's syndrome , Werner 's syndrome and Rothmund @-@ Thomson syndrome are caused by malfunctioning copies of RecQ helicase genes involved in the regulation of homologous recombination : BLM , WRN and RECQ4 , respectively . In the cells of Bloom 's syndrome patients , who lack a working copy of the BLM protein , there is an elevated rate of homologous recombination . Experiments in mice deficient in BLM have suggested that the mutation gives rise to cancer through a loss of heterozygosity caused by increased homologous recombination . A loss in heterozygosity refers to the loss of one of two versions — or alleles — of a gene . If one of the lost alleles helps to suppress tumors , like the gene for the retinoblastoma protein for example , then the loss of heterozygosity can lead to cancer . 
