Selective serotonin reuptake inhibitors (SSRIs) are antidepressants that are commonly used as first-line treatment of depression. Examples include Prozac, Zoloft and Paxil. However, 30-40% of affected people do not appear to benefit as well from these treatments.

The “grouchy” version of the SLC6A4 gene may explain some of this variation, as it is associated with a decreased response to SSRIs.

The molecular target of SSRIs is the 5-HTT serotonin transporter protein. People with the “grouchy” gene produce lower levels of this protein, therefore, they have a lower number of SSRI targets, which affects the efficacy of these commonly prescribed antidepressants.

Alternative antidepressants may be recommended for patients carrying the “grouchy” gene.