Objectives. Preliminary studies suggest that black men have shorter androgen receptor CAG repeat length compared with non-Hispanic whites. Because decreased CAG repeat length (in particular less than 20 repeats) may be associated with increased prostate cancer risk, these findings are potentially important in providing a hypothesis to explain the increased risk of prostate cancer in black men.

Methods. CAG repeat length in the androgen receptor (exon one) was determined by a polymerase chain reaction method in 130 non-Hispanic white and 65 black men. All men had prostate-specific antigen levels less than 4 ng/mL and normal digital rectal examinations. Men self-classified themselves into racial categories by a standardized questionnaire.

Results. For whites, the mean ± SD, median, and range of CAG repeat length were 21.0 ± 3.0, 21, and 9 to 28, respectively. For blacks, the mean ± SD, median, and range of CAG repeat length were 19.0 ± 3.0, 19, and 13 to 26, respectively. The mean and median CAG repeat length in blacks were statistically significantly shorter than in whites. Black men were twice as likely as whites to have fewer than 20 CAG repeats (56.9% versus 28.5%, P = 0.0001).

Conclusions. These data unequivocally demonstrate that androgen receptor gene CAG repeat length varies in a race-specific manner in men without evidence of prostate cancer.