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Background: The prevalence of stuttering is much higher in males compared to females. The biological underpinnings of this skewed sex-ratio is poorly understood, but it has often been speculated that sex hormones could play an important role.

Aims: The present study investigated a potential link between prenatal testosterone and stuttering. Here, an indirect indicator of prenatal testosterone levels, the Digit Ratio (2D:4D) of the hand, was used. As numerous studies have shown, hands with more "male" characteristics (putatively representing greater prenatal testosterone levels) are characterized by a longer ring finger compared to the index finger (represented as a lower 20:40 ratio) in the general population.

Study design, subjects, outcome measures: We searched for differences in the 2D:4D ratios between 38 persons who stutter and 36 persons who do not stutter. In a second step, we investigated potential links between the 2D:4D ratio and the multifaceted symptomatology of stuttering, as measured by the Overall Assessment of the Speaker’s Experience of Stuttering (OASES), in a larger sample of 44 adults who stutter.

Results: In the first step, no significant differences in the 20:40 were observed between individuals who stutter and individuals who do not stutter. In the second step, 2D:4D correlated negatively with higher scores of the OASES (representing higher negative experiences due to stuttering), and this effect was more pronounced for female persons who stutter.

Conclusions: The findings indicate for the first time that prenatal testosterone may influence individual differences in psychosocial impact of this speech disorder. (C) 2014 Elsevier Ireland Ltd. All rights reserved.