• A genetic variation where gain, loss, or exchange of DNA results in monoallelic loss of function mutations in a diploid cell. In the context of tumor suppressor genes, where a single copy is sufficient for functionality, loss of function for the second allele is associated with tumorigenesis.
  NCI Thesaurus
  U.S. National Cancer Institute, 2021
• Genetic phenomenon due to deletion or mutation in one allele of a polymorphic gene, as detected by expression after cell fusion; used as a test for tumor-promoting mutations; do not confuse with "loss of heterogeneity" which applies to diverse cell populations within a tissue.
  CRISP Thesaurus
  National Institutes of Health, 2006
• If there is one normal and one abnormal allele at a particular locus, as might be seen in an inherited autosomal dominant cancer susceptibility disorder, loss of the normal allele produces a locus with no normal function. When the loss of heterozygosity involves the normal allele, it creates a cell that is more likely to show malignant growth if the altered gene is a tumor suppressor gene.
  NCI Dictionary of Cancer Terms
  U.S. National Cancer Institute, 2021
• The loss of one allele at a specific locus, caused by a deletion mutation; or loss of a chromosome from a chromosome pair, resulting in abnormal HEMIZYGOSITY. It is detected when heterozygous markers for a locus appear monomorphic because one of the ALLELES was deleted.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2021