It has been proposed that the ratio of the second to fourth digits (2D:4D) may be a proxy of prenatal androgen exposure, such that low 2D:4D ratio is associated with high prenatal androgen exposure. The aim of the present study was to measure the 2D:4D ratio in 100 right- and non-right-handed individuals with intellectual disability of unknown idiopathic origin and compare them to a control group of 85 typically developing individuals. We also sought to determine whether sexually dimorphic traits, such as 2D:4D ratio, tend to be more pronounced on the right hand of these groups than on the left. Our results indicated that males had lower 2D:4D ratios than females in both groups, and individuals with intellectual disability had higher ratios only in their right hand compared to typically developing individuals. Further, right-handed individuals had lower ratios in both hands compared to non-right-handed individuals. Our results are discussed in relation to the "Geschwind-Behan-Galaburda theory of cerebral lateralisation" and Witelson's callosal hypothesis that differential levels of prenatal testosterone exposure will cause atypical cerebral laterality in individuals with intellectual disability, and the suggestion that this atypicality will become evident in the 2D:4D ratio (Manning, Scutt, Wilson, & Lewis-Jones, 1998).

中文翻译：

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智障人士的数字比例（2D：4D）：研究睾丸激素在脑侧偏的建立中的作用。

已经提出，第二数字与第四数字的比率（2D：4D）可以作为产前雄激素暴露的代表，使得低的2D：4D比率与高的产前雄激素暴露有关。本研究的目的是测量100名右手和非右手患者的2D：4D比率，这些患者具有特发性未知的智力残疾，并将其与85个典型发育个体的对照组进行比较。我们还试图确定这些人群的右手是否比左手更明显地表现出性二态性状，例如2D：4D比率。我们的研究结果表明，两组中男性的2D：4D比率均低于女性，而智障人士的右手比率高于正常发育个体。进一步，与非惯用右手的人相比，惯用右手的人的双手比率较低。我们的研究结果与“ Geschwind-Behan-Galaburda的大脑侧偏理论”和Witelson的骨os假说有关，即不同水平的产前睾丸激素暴露将导致智障人士出现非典型的大脑侧偏，并且这种非典型性将变得明显以2D：4D的比例显示（Manning，Scutt，Wilson，＆Lewis-Jones，1998）。