Genetics 101: Types of Genetic Testing

Baylor Genetics is a one-stop-shop for diagnostic genetic services and houses a number of specialty laboratory divisions based on the fundamentals of biology. These specialties include:

  • RNA Analysis: RNAseq (for the Undiagnosed Diseases Network), RT-PCR for SARS-CoV-2 detection (Infectious Diseases)
  • Biochemistry: Analyte and enzyme analyses, Global Metabolic Assisted Pathway Screen (Global MAPS), and respiratory chain enzymology
  • DNA Sequencing: Single genes, gene panels, custom gene panels, screening panels, exome, nuclear genome, and mitochondrial genome
  • Cytogenetics: Chromosome, chromosomal microarray, and FISH analyses
  • Cancer Genetics: Hereditary cancers and tumor analyses for genetic sequence, copy number, and rearrangements

RNA Analysis

In general, life is built around the need to produce tools to complete particular tasks and the need to store instructions for producing those tools. The tools are enzymes (usually special proteins) that help specific chemical reactions to occur. The instructions for these tools are stored in nucleic acids (RNA and DNA). Our cells store instructions in DNA and transcribe copies of those instructions into RNA molecules of various types. Messenger RNA molecules get translated to produce proteins that form structures or help to carry out chemical reactions. The archival nucleic acids are copied during reproduction and cell division.

There is abundant evidence pointing to an RNA origin for life. Since some RNA molecules can serve as both instructions and as enzymes, they solve certain problems in biology. That is, enzymes are needed to make the information storage molecules (RNA and DNA) but DNA and RNA are needed to make enzymatic proteins.

Transfer RNAs, ribosomal RNAs, and messenger RNAs act in a mutual agreement to produce proteins. Still, other RNA molecules are important in producing the transfer RNAs and splicing together the pieces of messenger RNAs. Some types of RNA help to form the protective caps at the ends of chromosomes or regulate gene expression.

By sequencing RNA, it is possible to tell what the cell is building or failing to build. Reverse Transcription PCR (RT-PCR) is the basis for our test to determine if the cell is attempting to build the Coronavirus SARS-Co V-2 that causes the disease COVID-19. Sequencing RNA also provides a way for determining if a change to the DNA instructions has resulted in a change in what the cell is planning to produce. While RNA sequence analysis is relatively new, it will become an increasingly important component of genetic analysis moving forward.

Biochemistry

Biochemical analysis is another important way to monitor what proteins and metabolites the cell is producing and whether or not they are normal. When gene sequencing does not make a clear prediction of consequence, biochemistry may be used to determine if the change to the DNA is significant.

Screening tests like our test, Global MAPS, can also help to focus a genetic investigation on a particular biosynthetic pathway. This is especially important in cases where DNA sequence analysis has failed to identify the underlying cause of a genetic disorder. Please keep in mind that when trying to establish a diagnosis, it is best to obtain samples when the patient is ill.

Biochemical analyses are also frequently used to monitor disease statuses and their response to therapeutic interventions. For example, monitoring metabolites can indicate if a specialized diet or medication is having the desired effect.

DNA Sequencing

DNA analysis is often used as part of a medical genetic evaluation. Advances in technology have reduced both the cost of DNA sequencing and the number of candidate genes that can be examined in parallel. Not only can DNA analysis frequently establish a diagnosis, but it can also allow for testing of family members to identify those at risk for developing a disease or for having an affected child.

DNA analysis is often used as an alternative to biochemical analysis because of cost efficiency, definitiveness, and predictiveness for family members. In fact, DNA testing can be used to predict risk for disease prior to the onset of symptoms in prenatal, postnatal, childhood, and adulthood stages of life.

In addition, DNA screening can identify reproductive risk even in the absence of a family history of the disease. During the sequence analysis, small spelling errors in the DNA are identified. However, not all genetic diseases are the consequence of a small change in a gene. Larger changes to part or all of a gene may be identified by special tests such as Southern hybridization analysis, multiplex ligation-dependent probe amplification (MLPA), or by array hybridization.

DNA analysis tools are also the mainstay of

Since most of the genes governing the production and function of the mitochondria are actually encoded by the nucleus, there are also issues of coordinating the expression genes and the delivery of gene products. The expertise and leadership of our mitochondrial testing division make it the first choice for mitochondrial testing.

Cytogenetics

Gene mutations are not the sole cause of genetic diseases. Imbalances in gene products, too much or too little, can also produce disease. Cytogenetic analyses such as chromosomal microarray analysis (CMA), chromosome analysis (karyotyping), and fluorescent in situ hybridization (FISH) can identify imbalances in the genetic material.

The latter two tests can also identify individuals who have a balanced rearrangement of their genetic material, conferring a reproductive risk despite being healthy. Cytogenetics is often utilized when there are multiple abnormalities prenatally or postnatally. In addition, it is used when there is a history of reproductive losses or when there is a significant reproductive risk for a chromosomal abnormality.

Cancer Genetics

Cancer genetics straddles many of the above disciplines. All cancers are genetic, but not all cancers are inherited. Defects in genetic replication, cell cycle control, cell differentiation, and cell contact inhibition contribute to cancer development and progression.

The BG cancer genetics division offers a comprehensive menu of tests to address the nuances of cancer genetics. Sequencing for inherited genetic changes can identify individuals with a cancer predisposition.

Other cancers may arise, not from inherited changes, but from acquired mutations to the genetic material. Some of these changes are genetic spelling errors that are identifiable by gene sequencing. Other changes involve altered gene copy number that can be identified by CMA, MLPA, or FISH analyses.

Some cancers involve genetic rearrangements that are often evaluated by FISH analysis. Cancers acquire changes as they progress. Thus, it may be necessary to perform more than one of these types of testing. These DNA analyses may also identify therapeutic targets and on-going treatment protocols.

Why Baylor Genetics?

The various testing divisions within the Baylor Genetics Laboratories mirror the fundamental processes for life itself. DNA organized as chromosomes stores the instructions for producing RNA, proteins, and other biochemical products. Analysis of the DNA, chromosomes, proteins, or other biochemical molecules can provide insight for diagnosis and medical care when the malfunction of these processes pose risk or create disease.

Through continuous innovation and research, Baylor Genetics is focused on improving healthcare throughout all of the divisions listed above. We are able to diagnose rare diseases and disorders because of our existing large-scale, high-throughput capabilities and our CLIA-certified, CAP–accredited laboratory.

To learn more about our genetic tests, visit: https://www.bcm.edu/research/medical-genetics-labs/tests.cfm

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