Single-stranded conformational polymorphism

A laboratory test used to separate single-stranded nucleic acids based on subtle differences in their DNA sequence, often a single base pair, which results in a different secondary structure and a measurable difference in mobility through a gel. Also called SSCP analysis. (NCI Thesaurus)

Trinucleotide repeat

Sequences of 3 nucleotides repeated in tandem on the same contiguous section of chromosome. A certain amount of normal (polymorphic) variation in repeat number with no clinical significance commonly occurs between individuals; however, repeat numbers over a certain threshold can, in some cases, lead to adverse effects on the function of the gene, resulting in genetic disease.

Base pair

Two nitrogen-containing bases pair together between double-stranded DNA; only specific combinations of these bases (e.g., adenine with thymine; guanine with cytosine) are possible, a fact which facilitates accurate DNA replication; when quantified (e.g., 8 base pairs, or bp), this term refers to the actual number of base pairs in a sequence of nucleotides.

Mutation

A change in the usual DNA sequence at a particular gene locus. Mutations (including polymorphisms) can be harmful, beneficial, or neutral in their effect on cell function. (NCI Thesaurus)

Missense mutation

A single base pair substitution that alters the genetic code in a way that produces an amino acid that is different from the usual amino acid at that position. Some missense mutations will alter the function of the protein. (NCI Thesaurus)

Deleterious mutation

A mutation that is documented to be associated with risk of disease.

Disease-causing mutation

A gene alteration that causes or predisposes an individual to a specific disease.

Frameshift mutation

An insertion or deletion involving a number of base pairs that is not a multiple of three, which consequently disrupts the triplet reading frame of a DNA sequence. Such mutations usually lead to the creation of a premature termination (stop) codon, and result in a truncated (shorter-than-normal) protein product. (NCI Thesaurus)

De novo mutation

An alteration in a gene that is present for the first time in one family member as a result of a mutation in a germ cell (egg or sperm) of one of the parents, or a mutation that arises in the fertilized egg itself during early embryogenesis. Also called new mutation. (NCI Thesaurus)

New mutation

An alteration in a gene that is present for the first time in one family member as a result of a mutation in a germ cell (egg or sperm) of one of the parents, or a mutation that arises in the fertilized egg itself during early embryogenesis. Also called de novo mutation. (NCI Thesaurus)

Predisposing mutation

A germline mutation that increases an individual’s susceptibility or predisposition to a certain disease or disorder. When such a mutation is inherited, development of symptoms is more likely, but not certain. Also called susceptibility gene. (NCI Thesaurus)

Point mutation

An alteration in a DNA sequence caused by the substitution of a single nucleotide for another nucleotide.

Founder mutation

A gene mutation observed with high frequency in a group that is or was geographically or culturally isolated, in which one or more of the ancestors was a carrier of the mutant gene. This phenomenon is often called a founder effect.

Carrier

In classical genetics, an individual who carries one deleterious allele for an autosomal recessive disorder. In clinical discussions, may refer to an individual who carries a deleterious allele that predisposes to disease.

Informative

In genetic testing, a test result that reveals definitively the presence or absence of the germline genetic alteration associated with the hereditary disorder being assessed. In linkage analysis, the ability to distinguish between maternally inherited and paternally inherited DNA markers (polymorphisms) within or near a given gene of interest.