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Different Types of Genetic Mutations and Variants - Explained

Our body is made up of billions of cells, and in each cell there are instructions, called genes, that make all the necessary structural components and chemicals for the body to work.

A variation in a gene that causes the gene to not work properly is called a mutation or pathogenic variant.

Before we begin, let’s have a quick crash course.

DNA is composed of long chains of chemical units called bases—Adenine (A), Cytosine (C), Guanine (G), and Thymine (T)—which form the structure of chromosomes.

These bases are arranged in groups of three called codons, which are read by cells to synthesize proteins, crucial for cellular functions.

Each codon specifies an amino acid, the building blocks of proteins, or signals such as start and stop commands for protein synthesis.

Only about 1-2% of DNA in the human genome is coding DNA, involved in protein synthesis, with the rest being non-coding DNA. This coding portion, known as exons, and the non-coding sections play essential roles in gene expression and regulation.

When the sequence of DNA bases in a gene is misread, it leads to the production of proteins that are incorrect, insufficient, or not produced at all. Such anomalies can result in genetic disorders. 

Identifying the responsible gene is the first step in diagnosing these conditions, followed by analyzing the specific sequence of DNA bases.

Genetic testing helps determine if an individual carries gene variants that may cause health issues. This testing is valuable for diagnosing genetic conditions in an individual or their family, predicting the likelihood of developing certain diseases like breast cancer.

Source: Genetics

Your genetics questions, answered.

Parents, we know you have many questions, with the main one being how do mutations and variants happen?

DNA mutations and variations usually happen due to small errors when cells divide and replicate their genetic material, which can be influenced by stress or environmental factors.

These genetic changes might include duplications or rearrangements of DNA segments.

While some mutations are inherited and present from birth, many develop over a person's lifetime due to these replication errors or environmental influences. Ultimately, not everything is passed on by a family member. Anyone can have a gene mutation or variant.

These mutations are mostly random and are not usually a cause for concern unless they result in health issues.

Genetic Variations

Genetic Variations

Genetic variations can occur in anyone, not just those with a family history of genetic conditions. Not all genetic changes are inherited; many are acquired randomly throughout a person's life.

1. Single Nucleotide Variant

Imagine changing a single letter in a word within a sentence; this is similar to a single nucleotide variant in DNA. Such variations that lead to the incorporation of a different amino acid in a protein are called missense variants. If the variation introduces a premature stop signal in the protein sequence, it is called a nonsense variant.

2. Deletion Variant

Sometimes, a segment of the gene might be missing from the genetic code, which is known as a deletion variant. This results in a genetic message that is incomplete or misread, potentially leading to the production of an incorrect protein.

3. Insertion Variant

An insertion variant involves extra DNA being added into the genetic code. This can extend the genetic message incorrectly or disrupt its normal reading, possibly leading to an inaccurate protein.

4. Repeat Expansion

A particular type of variation is the trinucleotide repeat expansion, where specific DNA sequences of three bases are repeated more often than normal within a gene. These repeats are part of the gene's usual pattern, but when excessively repeated, they affect how the gene functions.

Source: Genetics

Types of Mutations

Sometimes, cells make errors when copying their DNA, either inserting an incorrect base or missing one entirely as a strand is assembled.

Like genetic variations, mutations can also occur in anyone, not just those with a family history of genetic conditions. Not all genetic changes are inherited; they just happen by chance as we go through life.

There are two primary types of mutations:

  • Gene Mutations are changes that occur within a single gene.
  • Chromosomal Mutations are changes that affect entire chromosomes.

1. Genetic Mutations

Genetic Mutations

A. Point Mutations

Point mutations involve changes in one or a few nucleotides and occur at a specific point in the DNA sequence, typically during replication. If a mutation happens in one cell, it can be inherited by all subsequent cells derived from it.

Point mutations can be:

 

  • Substitutions, where one base is replaced by another. This type may only affect a single amino acid or sometimes have no impact at all. 

B. Insertions and Deletions (Indels)

These are point mutations where bases are either added or removed from the DNA sequence. Indels alter the way bases are read in groups of three, shifting the grouping in every codon that follows, which can lead to:

Frameshift Mutations, where the reading frame of the genetic message is shifted, potentially altering every subsequent amino acid and heavily affecting the protein's functionality.

2. Chromosomal Mutations

These involve changes in the number or structure of chromosomes, affecting gene locations and the number of gene copies. Types include:

  • Deletion: Loss of all or part of a chromosome.
  • Duplication: An extra copy of all or part of a chromosome is created.
  • Inversion: Parts of a chromosome are reversed.
  • Translocation: A chromosome segment breaks off and attaches to another chromosome.

Source: ETSU

Genetic Testing

Genetic Testing 1. Targeted Genetic Testing

This test searches for a specific known variant within a single gene that causes a genetic disorder, such as the HBB gene variant responsible for sickle cell disease. It's commonly used to check if family members also carry the variant, and by direct-to-consumer companies to analyze particular variants in certain genes for health risk information.

2. Single gene

This approach tests for any genetic changes in one gene and is used primarily to confirm or dismiss a diagnosis when a gene may contain multiple variants that could lead to the condition in question.

3. Gene panel

These tests examine multiple genes simultaneously to diagnose conditions when symptoms may correspond to various potential disorders, or the condition could be caused by variants in multiple genes, such as in the case of epilepsy which has hundreds of genetic causes.

 

Source: Medline Plus

4. Whole Exome Sequencing (WES)

WES is a genetic sequencing method that analyzes the coding regions of genes (exons), which make up about 1% to 2% of the human genome and are responsible for coding proteins. It is useful for diagnosing complex and elusive health conditions or when there is a family history of medical issues.

Whole exome sequencing has helped diagnose many genetic disorders, including Duchenne muscular dystrophy, cystic fibrosis, and Huntington's disease. In cancer research, WES investigates genetic influences on cancer susceptibility.

Sources: Yale Medicine, Applidx, Illumina

5. Whole Genome Sequencing (WGS)

WGS sequences an individual's complete (100%) DNA, capturing mutations both within and outside exons—including introns and non-coding regions. It is crucial for understanding all potential genetic disorders.

WGS enables precise medical interventions based on a patient’s unique genetic makeup, crucial for diagnosing rare diseases, cancer genomics, and pharmacogenomics. 

Sources: BioMed Central 

Importance of Genetic Mutations and Variants in Health

Importance of Genetic Mutations and Variants in Health

Disease-Causing Mutations

Point Mutation

  • Type of Mutation: Substitution
  • One base is incorrectly added during replication and replaces the pair in the corresponding position on the complementary strand.
  • Linked to sickle-cell anemia

  • Type of Mutation: Insertion
  • One or more extra nucleotides are inserted into replicating DNA, often resulting in a frameshift.
  • Linked to one form of beta-thalassemia
  • Type of Mutation: Deletion
  • One or more nucleotides is "skipped" during replication or otherwise excised, often resulting in a frameshift.
  • Linked to cystic fibrosis
  • Type of Mutation: Inversion
  • One region of a chromosome is flipped and reinserted.
  • Linked to Opitz-Kaveggia syndrome

 

Chromosomal Mutation

 

  • Type of Mutation: Deletion
  • A region of a chromosome is lost, resulting in the absence of all the genes in that area.
  • Linked to Cri du chat syndrome
  • Type of Mutation: Duplication
  • A region of a chromosome is repeated, resulting in an increase in dosage from the genes in that region.
  • Linked to some cancers
  • Type of Mutation: Translocation
  • A region from one chromosome is aberrantly attached to another chromosome.
  • Linked to one form of leukemia

 

Copy Number Variation

  • Type of Mutation: Gene amplification
  • The number of tandem copies of a locus is increased.
  • Linked to some breast cancers
  • Type of Mutation: Expanding trinucleotide repeat
  • The normal number of repeated trinucleotide sequences is expanded.
  • Linked to Fragile X syndrome, Huntington's disease

Source: Nature

Pharmacogenomics

Pharmacogenomics investigates the influence of genetics on drug response, with the aim of giving patients the right drug at the right dose and at the right time. Almost all patients carry one or more genetic variants which can alter their response to a drug, causing anything from a lack of response to serious, even fatal, drug toxicity. 

Source: Springer Link

Future Directions in Genetic Testing and Research

Future Directions in Genetic Testing and Research

Emerging technologies in genetic testing are transforming healthcare and research by presenting more detailed genomic evaluations. These technologies are crucial in the development of fetal precision medicine and are integrated into various stages of prenatal and reproductive care.

Additionally, the integration of genetic data into personalized healthcare is increasingly being realized through precision medicine. This approach tailors medical care to individual molecular profiles, helping healthcare systems provide better solutions. 

Source: Springer Link

Understand and Manage Genetic Conditions

Our bodies, composed of billions of cells, rely on genetic instructions—genes—to function correctly. However, errors can occur, leading to mutations or pathogenic variants that may disrupt normal protein production and cause genetic disorders. 

By examining the types of mutations, we can better understand the effects these changes can have on health.

About Fore Genomics

Fore Genomics is designed as the most comprehensive genetic screen possible for newborns, infants, and children. We want every family to have access to the best technologies available for their child's health. Genetic screening can be used prior to the onset of symptoms to lead to proactive management of genetic diseases. 

Our goal is simple: to give parents peace of mind and help children live healthier lives. 

Learn more about the 300+ conditions and medication interactions we screen for.

FAQs

What are genetic mutations and how do they differ from genetic variations?

Genetic mutations refer to changes in the DNA sequence that affect the gene's function, potentially leading to genetic disorders. Genetic variations are differences in DNA sequences among individuals that do not necessarily lead to disease.

How do genetic mutations and variations contribute to the development of diseases?

Genetic mutations and variations can influence the development of diseases in several ways. Mutations change the structure and function of proteins, leading to dysfunctional cellular processes and, ultimately, diseases. Variations can predispose individuals to diseases by affecting their genetic susceptibility.

What types of genetic testing methods are available to detect mutations and variations?

There are several genetic testing methods available to detect mutations and variations, including targeted genetic testing, single gene testing, gene panel testing, whole exome sequencing, and whole genome sequencing.

Can genetic testing accurately predict an individual's risk for developing certain conditions?

Genetic testing can often predict an individual's risk for developing certain genetic conditions accurately, especially for diseases caused by specific, well-understood genetic mutations. For example, tests for the BRCA1 and BRCA2 genes can indicate a high risk of developing breast and ovarian cancer.

How can genetic counseling help individuals and families understand their genetic test results?

Genetic counseling helps individuals and families understand the implications of genetic test results, including the risk of developing specific diseases, the impact on family members, and potential treatment or prevention strategies. Genetic counselors provide support and information, helping clients make informed decisions regarding their health care.

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