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Single Nucleotide Polymorphism (SNP) – Definition & Meaning

A single nucleotide polymorphism (SNP) is a common genetic variation where a single nucleotide differs at a specific position in the genome. SNPs influence disease risk and medication responses.

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Things worth knowing about "Single Nucleotide Polymorphism"

A single nucleotide polymorphism (SNP) is a common genetic variation where a single nucleotide differs at a specific position in the genome. SNPs influence disease risk and medication responses.

What Is a Single Nucleotide Polymorphism?

A single nucleotide polymorphism (abbreviated SNP, pronounced "snip") is one of the most common forms of genetic variation in the human genome. It occurs when a single nucleotide – one of the basic building blocks of DNA – differs between individuals or populations at a specific position in the genome. For example, at a particular location in the DNA sequence, one person may carry the nucleotide adenine (A), while another carries guanine (G).

By definition, a variant is classified as a SNP when the less common version (known as the minor allele) occurs in at least one percent of the population. The human genome is estimated to contain between 4 and 5 million SNPs. Many of these are located in non-coding regions of the DNA – segments that do not directly code for proteins – yet they can still be biologically significant by influencing how genes are regulated.

Biological Significance

Most SNPs have no direct harmful effects on health. However, many SNPs are associated with an increased or decreased risk of developing specific diseases. Examples include:

Cardiovascular diseases (e.g., heart attack, stroke)
Type 2 diabetes mellitus
Cancer (e.g., breast cancer, colorectal cancer)
Autoimmune conditions (e.g., rheumatoid arthritis, multiple sclerosis)
Psychiatric disorders (e.g., schizophrenia, depression)

SNPs can also affect how the body absorbs, metabolizes, and responds to medications. This field of study is known as pharmacogenomics. For instance, certain SNPs in genes responsible for drug metabolism – such as those encoding enzymes of the liver CYP450 system – can cause a patient to break down a medication faster or slower than average, directly affecting the drug efficacy and tolerability.

SNPs and Inheritance

SNPs are inherited from parents and remain stable across generations. Because neighboring SNPs on the same chromosome tend to be inherited together, they form patterns known as haplotypes. These inherited blocks of variants are especially valuable in genetic research, as they serve as markers linking specific regions of the genome to diseases or traits.

Diagnostic and Scientific Applications

In modern medicine and research, SNPs are used in a variety of important ways:

Genome-Wide Association Studies (GWAS): Researchers compare the frequency of specific SNPs in affected and unaffected individuals to identify genetic risk factors for diseases.
Personalized Medicine: SNP profiles help tailor therapies to the individual genetic background of a patient.
Predictive Genetic Testing: SNP analyses enable risk predictions for certain conditions, such as in oncology or cardiology.
Ancestry Analysis and Forensic Genetics: SNPs are used to determine familial relationships and assist in individual identification in legal medicine.
Biomarker Development: In clinical research, SNPs serve as biomarkers to predict treatment response and optimize therapeutic strategies.

Differences from Other Genetic Variations

SNPs are the most common and best-studied form of genetic variation, but other types also exist:

Insertions and Deletions (Indels): Short DNA segments are inserted into or removed from the genome.
Copy Number Variants (CNVs): Larger DNA segments are present in varying numbers of copies.
Microsatellites: Short, repetitive DNA sequences vary in the number of repeats.

Compared to these types of variation, SNPs are point-specific and therefore easier to analyze and standardize at large scale.

References

Strachan T, Read A. Human Molecular Genetics. 5th ed. CRC Press; 2018.
Gibbs RA et al. The International HapMap Project. Nature. 2003;426(6968):789-796. doi:10.1038/nature02168
National Human Genome Research Institute (NHGRI). Single Nucleotide Polymorphisms (SNPs). https://www.genome.gov/genetics-glossary/Single-Nucleotide-Polymorphisms. Accessed 2024.

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