Loss of heterozygosity (LOH) is a method of monitoring genetic deletions common in tumors for many types of cancer. LOH is manifested by severe allelic imbalance at a locus in a single-source DNA sample so that a true heterozygote almost appears as a homozygote since some of the chromosomes have a deletion present in the region of the locus being PCR-amplified.
Probably the only time that LOH would have an impact on human identity testing is if an archived clinical specimen from a tissue biopsy was used as a reference sample to identify someone from a mass disaster (see Chapter 24). However, it is worth being aware of the fact that normal and cancerous tissue from an individual can vary fairly dramatically in some instances in terms of their STR allele peak heights (Vauhkonen et al. 2004). An examination of a cancer biopsy tissue specimen compared to normal tissue with the nine STR loci present in the AmpFlSTR Profiler kit found that the D13S317 locus exhibited a severe peak imbalance consistent with that seen arising from LOH (Rubocki et al. 2000). The authors suggest that this LOH might be due to a deletion of 13q21-22 seen previously with prostate cancer (Hyytinen et al. 1999) that is near the physical location of D13S317 on chromosome 13.
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