Testosterone metabolism: a possible biological underpinning of non-verbal IQ in intellectually gifted girls

The extraordinary giftedness is apparently a unique manifestation of a mutual interconnection between genes and environment. One of the possible etiological factors of intellectual giftedness is testosterone which is believed to affect the brain organization and function. The aim of our study was to analyze associations between 2D:4D digit ratio (a proxy of prenatal testosterone) and/or salivary testosterone levels with non-verbal IQ in intellectually gifted girls. Fifty-one girls with an age range of 10 to 18 years and IQ scores higher than 130 were tested. Saliva samples were collected to obtain levels of salivary testosterone. 2D:4D digit ratio was measured on both hands as an indicator of prenatal testosterone. IQ parameters were assessed employing standardized set of tests. The CAG repeat polymorphism in exon 1 of the androgen receptor gene was analyzed to assess the sensitivity of androgen receptor. Testing of between-subjects effects proved significant interactions between right and left 2D:4D ratio, genetic variability in androgen receptor, and also salivary testosterone level with non-verbal IQ in gifted girls. Our results point out that the variability in parameters of androgenicity contributes to the variability of nonverbal IQ in gifted girls. However, the exact molecular mechanism of how testosterone acts on the brain and affects this cognitive domain remains still unclear.