Loss of heterozygosity

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Loss of heterozygosity (LOH) in a cell represents the loss of one parent's contribution to part of the cell's genome. A common occurrence in cancer, it often indicates the presence of tumor suppressor gene in the lost region. Often, the remaining copy of the tumor suppressor gene had been inactivated by a point mutation. The classical example is hereditary retinoblastoma, in which one parent's contribution of the tumor suppressor Rb1 is flawed. Although most cells will have a functional second copy, chance loss of heterozygosity events in individual cells almost invariably lead to the development of this retinal cancer in the young child.

LOH can arise via several pathways, including deletion, gene conversion, mitotic recombination and chromosome loss. The latter event is sometimes followed by duplication of the remaining chromosome.

Loss of heterozygosity can be identified in cancers by noting the presence of heterozygosity at a genetic locus in an organism's germline DNA, and the absence of heterozygosity at that locus in the cancer cells. This is often done using polymorphic markers, such as microsatellites or single nucleotide polymorphisms, for which the two parents contributed different alleles.

[edit] See also

• Tumor suppressor gene
• Loss of imprinting