Department of Psychology, Northumbria University , Newcastle upon Tyne , UK.
Front Endocrinol (Lausanne). 2013 Dec 5;4:185. doi: 10.3389/fendo.2013.00185. eCollection 2013.
The length ratio of the second to the fourth digit (2D:4D) is a putative marker of prenatal testosterone (T) effects. The number of CAG repeats (CAGn) in the AR gene is negatively correlated with T sensitivity in vitro. Results regarding the relationship between 2D:4D and CAGn are mixed but have featured prominently in arguments for and against the validity of 2D:4D. Here, I present random-effects meta-analyses on 14 relevant samples with altogether 1904 subjects. Results were homogeneous across studies. Even liberal estimates (upper limit of the 95% CI) were close to zero and therefore suggested no substantial relationship of CAGn with either right-hand 2D:4D, left-hand 2D:4D, or the difference between the two. However, closer analysis of the effects of CAGn on T dependent gene activation in vitro and of relationships between CAGn and T dependent phenotypic characteristics suggest that normal variability of CAGn has mostly no, very small, or inconsistent effects. Therefore, the lack of a clear association between CAGn and 2D:4D has no negative implications for the latter's validity as a marker of prenatal T effects.
第二指与第四指的长度比（2D:4D）是产前睾酮（T）作用的一个假定标志物。雄激素受体（AR）基因中的 CAG 重复数（CAGn）与体外 T 敏感性呈负相关。关于 2D:4D 与 CAGn 之间关系的结果存在分歧，但在支持和反对 2D:4D 有效性的争论中占据了重要地位。在这里，我对 14 个具有总共 1904 个受试者的相关样本进行了随机效应荟萃分析。研究结果在各研究之间具有同质性。即使是宽松的估计（95%CI 的上限）也接近零，因此表明 CAGn 与右手 2D:4D、左手 2D:4D 或两者之间的差异之间没有实质性关系。然而，对 CAGn 对体外 T 依赖性基因激活的影响以及 CAGn 与 T 依赖性表型特征之间关系的更仔细分析表明，CAGn 的正常变异性大多没有、很小或不一致的影响。因此，CAGn 与 2D:4D 之间缺乏明确的关联，并不意味着后者作为产前 T 作用标志物的有效性存在负面含义。
