In hereditary cancer syndromes, individuals are called heterozygous (having one or more dissimilar gene pairs) because they start life with a germline mutation in one of the alleles linked to cancer susceptibility, but it is balanced by a normal counterpart. These individuals are predisposed to cancer because all their cells have already sustained the first hit to cancer-linked genes. If the critically needed normal suppressor gene that balances this germline mutation is lost at some time during an individual's life, a condition called loss of heterozygosity (LOH) occurs.
![Loss of Heterozygosity](https://webarchive.library.unt.edu/eot2008/20081006124545im_/http://www.cancer.gov/images/Documents/a3a0ee76-1bc5-4490-aeaa-2248702c668f/cancer56.jpg)
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