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Glossary of Key Terms

Glossary of Key Terms

Acquired susceptibility mutation--A mutation in a gene that occurs after birth from a carcinogenic insult.

Allele--One of several mutational forms of a specific gene.

Autosomal dominant inheritance--Inheritance of a gene, which is located on a chromosome other than the sex (X or Y) chromosome, and which in single state, may give rise to a phenotype that may be expressed through two or more generations.

Deletion--Loss or removal of a sequence of DNA with the regions on either side being joined together.

Familial adenomatous polyposis (FAP)--An autosomal dominantly inherited predisposition to multiple adenomatous polyps of the colon and a risk for colorectal cancer that approaches 100% by age 60. The germ-line mutation for this disease is the APC gene, which stands for adenomatous polyposis coli. Other cancers, including papillary thyroid carcinoma, periampullary carcinoma, gastric cancer (particularly in FAP patients in Japan), small bowel cancer, pancreatic cancer, sarcomas and brain tumors, as well as desmoid tumors (which are not cancers) complicate this disease.

Frameshift--Deletions or insertions that alter the three-base-pair frame in DNA that are translated into protein.

Germ-line carriers--A mutation in a gene present in all cells in the body from birth.

Haplotype--The specific combination of alleles in a defined region of a chromosome.

Heterozygous--A patient with one or more pairs of dissimilar alleles is said to be heterozygous at that particular gene locus on homologous chromosomes.

Hereditary nonpolyposis colorectal cancer (HNPCC)--Autosomal dominantly inherited disease predisposing to colorectal cancer on a site-specific basis (Lynch syndrome I) and in association with a variety of extracolonic cancers (carcinoma of the endometrium, ovary, stomach, small bowel, and pancreas, and transitional-cell carcinoma) of the ureter and renal pelvis (Lynch syndrome II). Genes identified in this syndrome include hMSH2, hMLH1, hPMS1, and hPMS2.

Homozygous--A patient with identical alleles at the same locus of homologous chromosomes is said to be homozygous.

Incomplete penetrance--Absence of expression of the phenotype in an obligate gene carrier.

Inherited susceptibility mutation--A mutation in a gene that is inherited in Mendelian fashion, and thus present in all cells in the body from birth, which causes susceptibility to a given disease.

Insertion--The gain or addition of a sequence(s) of DNA not normally present.

Kindred--Individuals who are related by genetics or marriage to all other members of the particular group ("kindred" is often used interchangeably with "family").

Linkage analysis--Genes are said to be "linked" when they reside close together on the same chromosome. Statistical analysis of linkage of two genes is then expressed as a Lod score.

Missense mutation--A change in a DNA-base that results in a three-base-pair sequence that codes for a different amino acid than the original code.

Nonsense mutation--Any change in DNA that results in a three-base-pair sequence that does not code for an amino acid, and thus terminates the protein sequence.

Penetrance--The proportion of individuals with the genotype (such as hMSH2 germ-line carriers of HNPCC) who manifest the phenotype.

Promoter mutation--Any mutation in that part of DNA involved in binding of RNA polymerase to initiate transcription.

Splice mutation--A mutation resulting from imprecise removal of introns and joining of exons in RNA.

Stop codon--A three-base-pair sequence in DNA that does not code for an amino acid, and thus results in termination of the protein sequence.

Transcription--Synthesis of RNA on a DNA template.

Variable expressivity--Difference in the phenotype, such as age of onset or specific type of cancer, in an obligate germ-line carrier.

 
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