allele. Any one version of a particular gene, occupying the same position on a specific chromosome as other alleles of that gene and differing from the others by only one or a few nucleotides. Each human cell contains two copies of each gene; these may be identical, or they may be two different alleles.

BRCA1/BRCA2. Breast cancer susceptibility genes. These two genes normally produce proteins involved in DNA repair. Mutations in these genes are associated in certain populations with a high risk for breast cancer and a significantly increased risk for ovarian cancer—with or without a family history of those disorders. Specific alleles of BRCA1 and BRCA2 genes have been associated with increased risk of developing breast (60% vs. 12% general population rate) and ovarian (15-40% vs. 1.4% general population rate) cancers. Together, BRCA1 and BRCA2 mutations account for between 5 and 10 percent of all breast cancers.

CDC. Centers for Disease Control and Prevention, Department of Health & Human Services.

CLIA. Clinical Laboratory Improvement Amendments of 1988.

CMS. Centers for Medicare and Medicaid Services, Department of Health & Human Services.

complex disorder. A disorder associated with a combination of alleles of several different genes—in contrast with Mendelian, single-gene, disorders. Because of the prevalence of many complex disorders in the general population, they are sometimes referred to as “common diseases.”

dominant. In an individual with two different alleles for a particular gene, the dominant allele determines the observed phenotype.

epigenetics. Changes in an organism’s phenotype by changes in gene expression that are not a result of the organism’s genome sequence.

FDCA. Food, Drug, and Cosmetic Act of 1938.

GINA. Genetic Information Nondiscrimination Act of 2008.

GWAS. Genome-wide association study.

genotype. An individual organism’s entire, exact genetic makeup, including all its alleles—regardless of whether or not those alleles are expressed.

HIPAA. Health Insurance Portability and Accountability Act of 1996.

haplotype. A set of alleles on a chromosome that tend to be inherited together.

HapMap. A haplotype map of a consensus human genome. The HapMap is a catalog of common genetic variants that occur in human beings. It describes what these variants are, where they occur in human DNA, and how they are distributed among people within populations and among populations in different parts of the world.

heterozygous. Having two different variations (alleles) of a DNA sequence.

highly penetrant. See penetrance.

homozygous. Having two identical alleles for a particular DNA sequence.

informed consent. An ethical and legal requirement in both clinical practice and in research with human participants that is necessary to ensure that an individual patient or client is aware of the risks and benefits of participating in research or of undergoing a clinical procedure. The individual must be informed of the nature of the procedure, possible alternatives, and any costs and potential risks as well as benefits.

LDT. Laboratory-developed test.

MDA. Medical Device Amendments of 1976.

Mendelian disorder. A disorder that has a strong association with a single gene. Also called a single-gene disorder.

NHGRI. National Human Genome Research Institute, an institute of the National Institutes of Health.

NICE: National Institute for Health and Clinical Excellence (United Kingdom).

nutrigenomics: The study of how dietary constituents interact with specific genes to affect health and risk of disease.

penetrance. Within the universe of individuals who carry a particular

allele, the proportion that actually express a phenotype associated with that allele.

phenotype. The observable physical characteristics of an organism, as determined by its genetic makeup, epigenetic modifications, and typically, by environmental influences.

recessive. The traits encoded by a recessive allele in a particular gene will only be physically apparent if it is present in both copies of the gene and cannot therefore be “over-ridden” by a dominant allele.

SACGHS. Secretary’s Advisory Committee on Genetics, Health, & Society. (Refers to the Secretary of Health & Human Services.)

SNP. Single-nucleotide polymorphism. A variation within a genome wherein a single nucleotide differs from the consensus genome.

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