In genetics

Genetics

Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

, rs4680 (Val158Met) is a genetic variant.
It is a single nucleotide polymorphism

Single nucleotide polymorphism

A single-nucleotide polymorphism is a DNA sequence variation occurring when a single nucleotide — A, T, C or G — in the genome differs between members of a biological species or paired chromosomes in an individual...

 (SNP) in the COMT gene that codes catechol-O-Methyltransferase.
The single nucleotide substitution between G--> A results in an amino acid change from valine

Valine

Valine is an α-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...

 to methionine

Methionine

Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar. This amino-acid is coded by the codon AUG, also known as the initiation codon, since it indicates mRNA's coding region where translation into protein...

 at codon 158.

The A or Met allele is associated with lower enzymatic activity (due to thermoinstability), and with exploratory behaviour.

The polymorphism has been much studied in schizophrenia

Schizophrenia

Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...

 research but as of November 2011 meta-analysis in the SzGene database shows no or very little effect.

Several personality genetics studies have examined the association of the polymorphism with personality traits.