DNA provides the necessary information to construct proteins, which control normal development and structural function
The complete sequence of DNA for a particular organism is called a ‘genome’ and is composed of 3 billion bases
Approximately 1% of DNA is considered ‘coding DNA’ | Remaining 98% to 99% of DNA is non-coding
Once labelled “junk DNA,” non-coding DNA is now known to influence gene activity
Much about non-coding DNA is still not understood and remains an active area of genetic research
What are the different types of non-coding DNA and what do they do?
One primary function of non-coding DNA is serving as a regulatory element for genes
For example, non-coding DNA can turn genes on or off, thereby regulating gene activity and protein production
Introns (regions of non-coding DNA found in protein-coding exons) are eventually spliced out along the path to making messenger RNA | Introns do not directly code for proteins but are necessary for normal gene expression and regulation
Some types of regulatory elements are embedded in these non-coding regions
They serve as important binding sites that help control how a gene is read
Non-coding DNA also serves to protect chromosomes
Telomeres are repeated segments of non-coding DNA found on the ends of chromosomes that protect these ends from being manipulated or degraded when the DNA replicates prior to cell division
Genes that code for RNA
Some non-coding DNA segments hold the instructions for making RNA molecules such as: transfer RNAs (tRNAs), ribosomal RNAs (rRNAs), long non-coding RNAs (lncRNAs) and microRNAs (miRNAs)
These RNA transcripts are involved with multiple vital cellular processes and play an important role in the regulation of gene expression
Non-Coding DNA and Disease
While most mutations in the non-coding regions will have no impact, some DNA alterations can play an imporant role in health and disease
Some genetic variants in these regions are associated with genetic syndromes, such as myotonic dystrophy type 1 that is caused by expansion of CTG trinucleotide repeats in the non-coding region of the DMPK gene
Variants in non-coding DNA may also be related to more common, complex disorders, including heart disease and cancer
Therapies are being developed as research provides more clues as to the relationship between non-coding DNA and disease
What Test Can Identify Changes in Non-Coding DNA?
Whole Genome Sequencing (WGS)
WGS is the genetic test that looks at the entire genome, and therefore covers non-coding regions as well
WGS is generally considered in individuals who are on a diagnostic journey
For example, people with rare diseases or syndromes for whom testing of specific potentially disease-causing genes have not identified any disease-causing gene mutations
WGS analysis usually requires a sample (blood or saliva) from the patient and possibly other family members
Results from WGS will not always yield a definitive diagnosis or provide actionable results
WGS testing is most informative when an individual’s family members are also tested to clarify result interpretation
For example, a child and both parents (trio)
Extremely important before WGS analysis
The potential exists for results that are unexpected or not definitive
Genetic counseling is recommended before and after WGS analysis
Note: Counseling before any genetic testing serves to explain the limitations and the possible test results that could be informative or noninformative | Posttest counseling focuses on the results and focuses on health information, health surveillance, and the occasional finding of nonpaternity
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