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What kinds of gene variants are possible?
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Mutationsanddisorders

What kinds of gene variants are possible?

The DNA sequence of a gene can be altered in various ways, potentially affecting health depending on where the change occurs and how it impacts protein function.

Gene variants, also known as mutations, can have varying effects on health. The following are the primary types of gene variants:

Substitution

This type of variant replaces one DNA building block (nucleotide) with another.

  • Missense: A change that results in the replacement of one protein building block (amino acid) with another, which may alter the function of the protein.
  • Nonsense: A change that results in a stop signal, prematurely signaling the cell to stop building a protein. This results in a shortened protein that may be nonfunctional or broken down.

Insertion

An insertion changes the DNA sequence by adding one or more nucleotides to the gene, which may cause the resulting protein to function improperly.

Deletion

A deletion removes at least one nucleotide in a gene. Small deletions remove one or a few nucleotides, while larger deletions can remove an entire gene or several neighboring genes.

Deletion-Insertion

This occurs when a deletion and insertion happen at the same time in the same location. At least one nucleotide is removed and at least one is inserted. This is also known as an indel variant.

Duplication

A duplication occurs when a stretch of one or more nucleotides is copied and repeated next to the original DNA sequence.

Inversion

An inversion changes more than one nucleotide by replacing the original sequence with the same sequence in reverse order.

Frameshift

A reading frame consists of groups of three nucleotides. A frameshift occurs when an addition or loss of nucleotides shifts the grouping, changing the code for all downstream amino acids and usually resulting in a nonfunctional protein.

Repeat expansion

This is a variant that increases the number of times a short DNA sequence (such as a trinucleotide or tetranucleotide repeat) is repeated in a row, which can cause the resulting protein to function improperly.

Frequently Asked Questions

nonsense mutation introduces a premature stop codon, truncating the protein and often rendering it nonfunctional. A frameshift mutation, caused by adding or removing nucleotides not in multiples of three, shifts the reading frame for the entire downstream sequence, usually producing a completely altered and usually nonfunctional protein. Both can cause severe disease, but the specific impact depends on the protein’s role.
Indel mutations are typically identified through sequencing methods that provide read lengths long enough to span the altered region, such as next‑generation sequencing (NGS) panels or whole‑exome sequencing. Bioinformatic pipelines align reads to a reference genome and flag gaps or extra bases that indicate insertions or deletions. Confirmation may be done with PCR and Sanger sequencing for precise breakpoint mapping.===
Yes. Even a single base change can have major effects if it occurs in a critical region of a gene, such as a splice site, a catalytic domain, or a regulatory element. Classic examples include cystic fibrosis (a missense mutation in CFTR) and sickle cell anemia (a single base change in hemoglobin).
missense mutation changes one amino acid in the protein chain. Depending on where the change occurs, it can alter the protein’s shape, stability, or interaction with other molecules, potentially reducing or enhancing its function. Clinically, this can lead to diseases ranging from mild enzyme deficiencies to severe metabolic disorders.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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