Interactions among impulsiveness, testosterone, sex hormone binding globulin and androgen receptor gene CAG repeat length

Impulsive personality phenotype has been extensively related with genetic and hormonal factors. This study has two objectives: a) to analyse the interactions between testosterone levels and CAG repeat length polymorphism as a modulator of androgen receptor (AR) sensitivity with regard to impulsiveness traits, and b) to evaluate the contribution of other biological variables as Luteinising Hormone, Follicle Stimulating Hormone, Sex Hormone Binding Globulin (LF, FSH, SHBG) and albumin in the relationship between testosterone levels and AR CAG length polymorphism with impulsiveness. A sample of 105 healthy males (mean age 26.71 ± 9.68 SEM) was analysed resulting in three groups of subjects according to CAG repeat lengths. Impulsiveness was measured through the Barratt's Impulsiveness Personality Scale, including three components: Motor Impulsiveness, Cognitive Impulsiveness and Non-Planning Impulsiveness. A series of ANOVAS and linear regression models predicting impulsiveness scales were conducted. Age, hormones, CAG repeat length and hormone × CAG repeat interactions were included in the regression models as independent variables. Results show that subjects with short or medium CAG repeat length tended to show higher impulsiveness phenotypes compared to long CAG repeat. The interaction between Free Testosterone and CAG, and between SHBG and CAG accounted for differences on impulsiveness (R: .47, R2: .22 and R: .43; R2: .18, respectively).This pattern was especially observed for the short CAG repeat group and Motor Impulsiveness.