The Grouchy gene is a genetic variant of gene 5-HTT which is designated 5-HTTLPR. 5-HTT provides with the instructions necessary to make the serotonin transporter. People with the grouchy version have lower transporter levels.

Genetically, 5-HTTLPR variation is due to size difference in the region of the gene. There are two variants a long form and a short form or the grouchy gene. Individuals with the short form make lower levels of less active transporters.

The grouchy gene is also associated with increased risk for a variety of psychological conditions like depression, bipolar disorder, attention deficit disorder and Alzhiemer’s disease as well as with addictive behaviors and sudden infant death syndrome.