While birth control pills are usually effective at preventing pregnancy, there is a small risk that they’ll fail. That’s been blamed on user error - forgetting to even one pill on time could reduce its efficacy. New research has indicated that other factors may be at work, however. Scientists have identified a small change or variation in a gene that encodes for an enzyme, which can break down hormones that are often used in contraceptives. The gene is only supposed to be expressed in childhood. But the research, reported in Obstetrics & Gynecology, suggests that a small percentage of women with a variant of that gene continue to produce that enzyme into adulthood.
"The findings mark the first time a genetic variant has been associated with birth control," said the lead author of the report Aaron Lazorwitz, MD, an assistant professor of Obstetrics and Gynecology at the University of Colorado School of Medicine.
In this research, the scientists assessed data from 350 healthy women that had a contraceptive implant for at least twelve and up to 36 months. They found three genetic variants in the participants. One of the variants, CYP3A7*1C, initiated the expression of a protein normally expressed in infanthood, CYP3A7. That protein is an enzyme that can change the metabolism of hormones.
The researchers suggested that women carrying this gene variant might break down birth control hormones so quickly that it renders their contraception ineffective. Carriers of the variant were found to have birth control levels that were too low to suppress ovulation consistently.
"That enzyme breaks down the hormones in birth control and may put women at a higher risk of pregnancy while using contraceptives, especially lower dose methods," Lazorwitz explained. "When a woman says she got pregnant while on birth control the assumption was always that it was somehow her fault. But these findings show that we should listen to our patients and consider if there is something in their genes that caused this."
Pharmacogenomics is a burgeoning field that shows how the gene sequences a person carries affects their response to drugs. It has the potential to transform healthcare, and women’s health dramatically. The study authors note that these findings, in particular, can have important consequences; unintended pregnancies can have huge ripple effects.
Lazorwitz is hopeful that this work will help create precise medicine that can help meet individual patient needs.
"As more genetic data becomes available, clinicians may need to consider adding genetic predisposition to increased steroid hormone metabolism in their differential diagnosis for unintended pregnancies in women reporting perfect adherence to hormonal contraceptive methods," he said.
Learn more about pharmacogenomics from the video above by Mayo Clinic.