Genetic Testing 101: Types of Testing and What They Can Reveal

A primer on genetic terminology and genetic testing

Genetic testing has revolutionized the way we understand our health. By examining our DNA, tests can provide valuable insights into disease risks, some of which can have actionable outcomes. In this blog post, we'll take a deep dive into the various types of genetic testing available and what they can reveal about you.

Let’s start with some basic definitions that will be helpful background for the next few blog posts:

Genetics: Genetics is the branch of biology that studies genes, heredity, and variation in living organisms.

Central Dogma of Biology: The central dogma of molecular biology explains the concept of how genetic information in DNA goes from DNA to RNA, to then make a functional product, a protein. Genetic changes can have consequences on how proteins are formed and function, as well as how much is there.

DNA: DNA is a molecule that carries the genetic instructions necessary for the growth, development, function and reproduction of living organisms.

Chromosome: Chromosomes contain genetic material (DNA) and are responsible for carrying and organizing an individual's genetic information. Humans typically have 46 chromosomes, 23 pairs.

Gene: A segment of DNA that contains instructions for making a specific protein.

Exon: the segments of a gene that code for a protein. Mutations in exons can have significant effects on an individual's health.

Intron: non-coding segments of a gene. They are transcribed into RNA but are not translated into proteins. While they don't code for proteins, there can be effects on intron mutations on gene expression.

Nucleotide: Nucleotides are the building blocks of DNA and RNA. DNA nucleotides are the A, T, G and C’s you see in your sequence.

Allele: An allele is a variant form of a gene located at a specific position on a chromosome. Alleles can differ in their sequence and can lead to variations in traits or diseases. Your allele at a specific position is the letter that you have there. You have two alleles at every position (one from each parent).

SNP: A SNP is a variation at a single position in a DNA sequence among individuals. It is the most common type of genetic variation, and SNPs can influence susceptibility to diseases, traits, and responses to drugs.

Mutation: A mutation is a change in the DNA sequence of an organism. It can occur due to various factors, including environmental factors or errors during DNA replication. Mutations can be responsible for genetic diversity and may lead to new traits, though they can also cause genetic disorders. A SNP is one type of mutation.

De Novo Mutation: a genetic mutation that is not inherited from parents but arises spontaneously in an individual.

Autosomal Dominant: a pattern of inheritance where a single copy of a mutated gene is enough to cause a particular trait or disease. That individual is called heterozygous for a specific mutation.

Autosomal Recessive: a pattern of inheritance where two copies of a mutated gene are needed to express a particular trait or disease. This is where you hear the term carrier when it comes to particular diseases. A carrier is someone who has one copy, and ‘carries’ the mutation but does not have the disease. It only becomes a concern when having children, if the other partner also is a carrier (see carrier screening below).

Types of Sequencing:

There are various types of genetic testing, each with its own unique focus and applications. From disease-specific gene panels to comprehensive whole genome sequencing, it’s important to know the different approaches to genetic testing and how they contribute to our understanding of genetic variations and health-related information.

Snp Array: A SNP array analyzes SNPs across the genome to identify variations associated with certain traits or diseases. It's useful for broad population studies and ancestry analysis but may not provide detailed health information.

A SNP array looks at specific letters within words.

Gene Panel: Gene panels focus on specific genes associated with a particular condition or disease area. However, it only includes the genes of interest and if there are new genetic discoveries, a new gene panel may be needed.

A gene panel looks at some of the full words.

Whole Exome Sequencing (WES): WES analyzes the exons (coding regions) of genes, providing a more comprehensive view compared to gene panels. It can be useful for diagnosing a wide range of genetic disorders. If you have WES data, it can be referenced again in the future if there are specific health concerns or new genetic discoveries in coding regions. One downside of WES data is that it can sometimes provide too much information, and most of it won’t be useful or relevant to your health. It is typically not covered by health insurance and is used a lot for research purposes.

WES looks at all the words.

Whole Genome Sequencing (WGS): WGS examines the entire genome (introns and exons), providing the most comprehensive genetic data. WGS is mainly used in research. Even more so than WES, WGS provides an overwhelming amount of information that can be difficult to sort through, and a lot of it won’t be relevant to your health. Like WES, once you have this data, it can be referenced again in the future. Insurance coverage is also unlikely.

WGS includes all the sentences.

Types of Genetic Testing

Focused Disease Area

When searching for genetic mutations associated with a specific medical condition, gene panels are often used. These panels focus on genes known to be linked to that particular disease. Connective tissue disorders like the Ehlers-Danlos Syndromes are detected this way (with the exception of hypermobile EDS right now). GeneDx and Invitae are the most common companies that healthcare providers use for this testing.

Heritable Disorders of Connective Tissue Panel - GeneDx

Invitae Connective Tissue Disorders Panel

Invitae Ehlers-Danlos Syndrome Panel

These tests need to be ordered by a healthcare provider. Invitae also works with genome medical to set you up with a provider who can order testing online.

Carrier Screening

Carrier screening is a type of genetic testing used to identify individuals who carry a single copy of a mutated gene associated with a recessive genetic disorder. It is often done before or during pregnancy to assess the risk of passing on such disorders to offspring.

Pharmacogenomic Testing

Pharmacogenomic testing can help determine how your genes may affect your body's response to medications. This can help healthcare professionals determine the most effective treatments for you.

Karyotyping

Karyotyping is used to examine an individual's chromosomes, which can help diagnose chromosomal abnormalities, such as Down syndrome. It provides a broad view of the structure and number of chromosomes in an individual's cells.

Direct to Consumer: Ancestry DNA / 23 and Me

While Ancestry DNA and 23andMe have become popular for ancestry purposes, they also provide limited health-related information. Downloading raw data and uploading it onto different platforms has become a popular way for people to try and use that genetic data for more than it was intended. It’s important to be cautious when relying on these services for medical insights, as they may not offer the same level of clinical validation as other medical-grade genetic testing providers. More on this is coming in the next blog post!

Thanks for tuning in to Genetics 101 (don’t worry, there isn’t a quiz). I hope this resource will be a helpful primer for the genetic blog posts coming soon!

Subscribe to follow along, including future blog posts on genetic testing for the Ehlers-Danlos Syndromes and direct-to-consumer genetic testing.