Gene Test Procedures
DNA sequencing is a laboratory technique to determine the exact sequence of base pairs (A, C, G, and T) in a DNA molecule. It includes any method or technology that is used to determine the sequence of the base pairs in a strand of DNA. The base pairs of a small fragment of DNA are sequentially identified from signals emitted as each fragment is re-synthesized from a DNA template strand. Using this process the nucleotide sequence for a segment of DNA, for example, a gene of interest, can be determined.
Next Generation Sequencing
The concept behind Next Generation Sequencing (NGS) technology is similar to traditional DNA sequencing. The bases of a small fragment of DNA are sequentially identified from signals emitted as each fragment is re-synthesized from a DNA template strand. NGS extends this process across millions of reactions in a massively parallel fashion, rather than being limited to a single or a few DNA fragments. This advance enables rapid sequencing of large stretches of DNA base pairs spanning entire genomes. NGS allows for rapid analysis of multiple genes at a considerably lower cost than traditional sequencing techniques. This technology has brought affordable exome sequencing to the clinical setting.
Recently, new genetic testing panels for hereditary breast, ovarian, and other cancers using next generation sequencing have been introduced. These panels currently are geared toward individuals who test negative for high penetrance genes or have a family history suspicious of more than one hereditary cancer syndrome. Current limitations include an unknown percentage of variants of uncertain significance, uncertainty of level of risk associated with most of the genes on the panels, and a lack of clear guidelines for surveillance measures for carriers of some mutations.
Certain large genomic rearrangements are not detectable by sequence analysis of the coding and flanking intronic regions of genomic DNA, thereby necessitating supplementary testing in some cases. A variety of methods that can identify deletions/duplications include quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA) and chromosomal microarray (CMA) that includes the gene of interest.
Family-Specific Mutation Analysis
A family-specific disease-causing mutation is a sequence alteration observed that causes or predisposes to a particular disease. This testing is for the specific disease-causing mutation previously identified in a family member.