The “grouchy” gene is a genetic variant in the SLC6A4 gene (designated 5-HTTLPR) that gives instructions to make a serotonin transporter. Serotonin, often called the ‘happiness molecule’ is responsible for feelings of pleasure and wellbeing. There are two common variants of the gene, a short (S) allele, or the “grouchy” gene and a long (L) allele. These variants are associated with differences in the number of serotonin transporters produced in the brain.
Individuals with the “grouchy” gene or the S allele make reduced numbers of serotonin transporters in the brain, which may increase the risk of mood disorders such as anxiety and depression.

The “grouchy” gene is also associated with increased risk for a variety of psychological conditions like depression, bipolar disorder, attention deficit disorder and Alzheimer’s disease as well as with addictive behaviours and sudden infant death syndrome. However, it should be noted that the presence of the “grouchy” gene is not a definitive indicator of increased risk of anxiety and depression.