Evidence that the CAG repeat in the androgen receptor gene is associated with the age-related decline in serum androgen levels in men

In men over 30 years old, serum levels of testosterone (T) decrease with ag e. A shorter polymorphic CAG repeat length in exon 1 of the androgen recept or (AR) gene is associated with higher transcription activation by the AR. We determined the number of CAG repeats for 882 men aged between 40 and 70 years from the Massachusetts Male Aging Study (MMAS). MMA.S is a population -based random sample survey of men for whom baseline (1987-1989, mean age 5 3 +/- 8 years) and follow-up (1995-1997, mean age 61 +/- 8 years) serum hor mone levels were available. Multiple linear regression was used to determin e ii CAG repeat length would be predictive of hormone levels at follow-up. Hormone levels measured included T, free T, albumin-bound T, dihydrotestost erone (DHT), sex hormone-binding globulin (SHBG) and luteinizing hormone (L H). The CAG repeat length was significantly associated with T (P=0.041), al bumin-bound T (P=0.025) and free T (P=0.003) when controlled for age, basel ine hormone levels and anthropometrics. Follow-up levels of T decreased by 0.74% +/- 0.36 per CAG repeat decrement. Likewise, the percentages of free and albumin-bound T decreased by 0.93% +/- 0.31 and 0.71% +/- 0.32 per CAG repeat decrement respectively. These results suggest that androgen levels m ay be modulated by AR genotype.