Genetic Marker Licensed to Mayo Clinic

A new genetic test that will help physicians identify patients who are likely to have side effects from drugs commonly used to treat depression has been licensed nonexclusively to the Mayo Clinic (Rochester, MN, USA) by Pathway Diagnostics, Inc. (Malibu, CA, USA).

The test detects a key genetic marker, 5HTTLPR, which identifies people who respond differently to antidepressants, including selective serotonin reuptake inhibitors (SSRI). SSRIs act specifically by binding to the serotonin transporter, and increase the concentration of the neurotransmitter serotonin in the synapse. These medications include fluoxetine (Prozac), sertraline (Zoloft), paroxetine (Paxil), citalopram (Celexa), and escitalopram (Lexapro). The test will be offered to patients through Mayo Medical Laboratories (MML), the reference laboratory for Mayo Clinic.

The 5HTTLPR biomarker has potential to improve management of patients with major depression and others who benefit from SSRI treatment. It provides unique information relating to drug response, side effects, and compliance. The Long/Long (L/L) genotype confers compliance to an SSRI, whereas the Short/Short (S/S) genotype indicates an increased compliance with a noradrenergic and specific serotonergic antidepressant.

The 5HTTLPR test is among the growing list of pharmacogenomic tests Mayo offers to help physicians personalize treatment options. Pharmacogenomics individualizes drug selection and dosing based on a person's genomic makeup and helps determine specific medications and dosages to avoid adverse drug reactions.

"The serotonin transporter genotype assists the physician in making a better choice of antidepressant medications for their specific patient,” said Dennis O'Kane, Ph.D., director of the Nucleotide Polymorphism Laboratory at Mayo Clinic, which validated the serotonin transporter testing. "Patients can be prescribed antidepressants that have a greater probability of being effective in their individual case, based upon their serotonin transporter genotype used in conjunction with CYP450 genotyping testing. Depending upon genotypes, some patients should respond well to SSRIs, some may respond to SSRIs but more slowly, and some patients may respond more effectively to non-SSRI antidepressants.”

Published studies have estimated that 30% of patients treated with existing antidepressant medications do not improve. In addition, 90% experience side effects, and 30-40% do not respond to the first drug regimen. "Prescribing a correct antidepressant for the specific patient may increase the likelihood of patient compliance and decrease the loss of patients to follow-up,” said Dr. O'Kane.



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