October 27, 2011

October 27, 2011


New Genetic Associations For Testosterone Levels in Men


Welcome to another day in my life. Today is Thursday and I hope you are having a safe and great week so far. It is another busy day for Dab the AIDS Bear and me. We are having a photo shoot for a Florida Department of Health HIV/AIDS ad and article today.

I have talked about hormone replacement for men with HIV/AIDS in my blog a few times. Now I would like to share some of the latest information on the subject.

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.

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 the G version of rs12150660 near the SHBG gene was associated with lower blood testosterone levels. They also found that the T version of rs6258, located within SHBG, was independently linked to lower levels of testosterone.

(23andMe customers can view their data for these and other SNPs in the Sex Hormone Regulation Preliminary Research report.)

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 rs12150660 and rs6258 associated with lower testosterone levels were also linked to lower concentrations of SHBG. Moreover, the SHBG proteins in men with the T version of rs6258 bound testosterone poorly compared to those in men without the T version.

Previous studies identified associations between variants in SHBG and lower levels of the SHBG protein and are included in our Sex Hormone Regulation report. The new study by the CHARGE consortium builds on these 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.”

So for you long time HIV/AIDS survivor and/or those from late 40s and older; this is something you might want to discuss with your health care provider.

Until we meet again; here's wishing you health, hope, happiness and just enough.



big bear hug,





Daddy Dab