A consortium that includes researchers from UAB has identified genetic markers that influence testosterone and estrogen levels in the bloodstream, according to a study published online recently in PLoS Genetics.
| SHBG is the main carrier of testosterone and estrogen in the bloodstream and helps to regulate their effects in tissues and organs. |
The results reveal specific genetic differences that influence each person’s amount of a key protein, sex hormone binding globulin, which was shown to determine the sex hormone levels. The team also found that the SHBG genetic markers occur near genes that control liver function and type 2 diabetes risk, which is further evidence of a link between metabolic and reproductive systems in men and women.
SHBG is the main carrier of testosterone and estrogen in the bloodstream and helps to regulate their effects in tissues and organs. The protein also has been linked by past studies to chronic diseases, including diabetes and hormone-sensitive breast and prostate cancers.
In the current study, investigators examined the human genomes of 21,791 men and women to determine which genes most influence SHBG levels. Investigators validated the results from this genome-wide association study in another 7,046 men and women. The effort identified 12 single-nucleotide polymorphisms — small variations in the DNA code — associated with the concentration of circulating SHBG in the bloodstream.
These SNPs, however, combined to explain just 16 percent of the SHBG variation seen in men and eight percent in women. This suggests that as yet unknown, nongenetic factors play the major role in determining SHBG levels.
The study was led by Boston University School of Medicine and the University of Exeter in the United Kingdom, and carried out in partnership with the Coronary Artery Risk Development in Young Adults study and the Cohorts for Heart and Aging Research in Genetic Epidemiology consortium. Melissa F. Wellons, M.D., assistant professor in the UAB departments of Medicine and Obstetrics and Gynecology, represented the CARDIA study and served on the current study’s main writing group.
“Arriving at these important findings required tremendous collaboration among individual investigators and the studies they represented,” Wellons said. “Our findings provide clues to the most important pathways that connect SHBG and metabolic diseases.”