Testosterone sometimes gets a bad rap. Although scientists no longer demonize it as the “aggression hormone,” its use is still considered a form of illegal “doping” in most sports. Setting controversies aside, this hormone certainly plays important roles in health and development. During puberty in boys, testosterone is responsible for facial and pubic hair, accelerated growth, and a deepening voice. Blood testosterone levels are also tied to overall health in men–studies have linked lower concentrations to cardiovascular disease, obesity, type 2 diabetes, and osteoporosis, among other conditions.
While non-genetic factors like age (levels are usually lower in older men), body mass index (BMI), and smoking are known to influence blood testosterone levels, genes also play a role. A study in male twins showed that genetics accounts for up to 65% of the variation in blood testosterone between individuals. However, up until this month, very little was known about the genetic factors responsible for this variation.
In a new study published in PLoS Genetics, researchers from the CHARGE Sex Hormone Consortium analyzed DNA from over 14,000 men of European descent and identified SNPs associated with low blood testosterone. The authors reported that a variant near the SHBG gene was associated with lower blood testosterone levels.
The fact that variations in SHBG are linked to testosterone levels may not be surprising because SHBG codes for a protein that binds testosterone in the blood. With additional experiments, the researchers observed that the versions of and associated with lower testosterone levels were also linked to lower concentrations of SHBG. Moreover, the SHBG proteins in men with the T version of bound testosterone poorly compared to those in men without the T version.
The new study by the CHARGE consortium builds on earlier findings by pinpointing additional factors and elucidating some of the biological reasons for their effects. The authors suggest that the genetic factors identified thus far have effects comparable to non-genetic factors on testosterone levels and could be used clinically to identify men who are at risk for low testosterone levels. Says lead author Professor Claes Ohlsson from the University of Gothenburg: “It is very interesting that the genetic contribution of the identified genetic variants to testosterone concentrations is substantial.”
