Low T refers to a deficit in body levels of testosterone, the male sex hormone. Low T results from low production of T and/or impaired transport of T in the bloodstream. Now, a new study sheds light on the genetic regulation of T levels by identifying the genetic markers for a T-related protein, sex hormone-binding globulin (SHBG). The hormone is responsible for transporting sex hormones (male and female) within the bloodstream.
Sex Hormone Binding
Sex hormones bind to SHBG and are carried to various bodily organs and tissues. It has been linked to chronic diseases such as hormone-related cancers (breast and prostate) and type 2 diabetes. It has been shown that half of the variation in bloodstream SHBG levels is attributable to one’s parents. This strongly implies that genetics plays a major role in the production of SHBG. Until now, the genes that elaborate SHBG had not been identified. With the new study, led by Boston University School of Medicine and the University of Exeter in the UK, two new pieces of the puzzle have emerged:
- We now know the specific genes that control the production of SHBG.
- We’ve also learned that these genes lie near others that control the metabolism of carbohydrates and fats, the liver and type 2 diabetes.
This second fact is important, because it demonstrates a link between the reproductive and metabolic systems in humans. Although the results are important, it should be pointed out that only 16 percent of the variation in SHBG concentrations in men (and eight percent in women) can by tied to the 12 single nucleotide polymorphisms (variations in DNA sequence) detected at the gene site. This means that a host of other factors play a role in SHBG levels. However, the fact that the genes were twice as significant in men as in women for SHBG variations may help explain differences in type-2 diabetes that are caused by gender differences.
The study was authored by Dr. Andrea Corviello, an endocrinologist at the Boston Medical Center. It is part of the famous Framingham Heart Study and included 15 investigators from a consortium that performs epidemiologic studies, the Cohorts for Heart and Aging Research in Genetic Epidemiology. The study looked at DNA from almost 22,000 individuals, and then validated its results by examining an additional 7,000 people. It will be interesting see how Low T is related to low SHBG concentrations in the bloodstream. It may be possible some day in the future to cure Low T with genetic therapy, and this study is an important clue in that quest.