The second-to-fourth digit ratio (2D:4D) has been associated with sexual dimorphism, with a lower 2D:4D in males. A large body of research has relied on the 2D:4D as a proxy for prenatal androgen exposure, and includes reports of relationships between 2D:4D and a wide range of human traits. Here, we examine the validity of the 2D:4D proxy by studying the association between 2D:4D and classical Congenital Adrenal Hyperplasia (CAH) due to 21-hydroxylase deficiency, a condition characterized by excessive prenatal exposure to androgens during most of the gestational period. To this end, we retrospectively examine 513 serial radiographs of the left hand obtained clinically in 90 youth with classical CAH (45 female) and 70 control youth (31 female). Replicating previous reports, we observe associations of the 2D:4D with sex (lower 2D:4D in males) and age (increase of 2D:4D through development). However, we find no evidence for differences in 2D:4D between CAH and controls (full sample: β = −0.001 (−0.008, 0.006); females: β = −0.004 [−0.015, 0.007]; males: β = 0.001, [−0.008, 0.011]). Although our findings do not rule out a small association between the 2D:4D and CAH, they cast doubt on the usefulness of the 2D:4D as a biomarker for prenatal androgen exposure in behavioral research.

第二与第四指的比例（2D：4D）与性别二态性有关，男性的 2D：4D 较低。大量研究依赖 2D:4D 作为产前雄激素暴露的替代指标，其中包括 2D:4D 与多种人类特征之间关系的报告。在这里，我们通过研究 2D:4D 与 21-羟化酶缺乏导致的经典先天性肾上腺增生 (CAH) 之间的关联来检验 2D:4D 代理的有效性，这种疾病的特征是在妊娠期的大部分时间里过度接触雄激素。为此，我们回顾性检查了 90 名典型 CAH 青少年（45 名女性）和 70 名对照青少年（31 名女性）临床获得的 513 张左手系列 X 光片。重复之前的报告，我们观察到 2D:4D 与性别（男性中 2D:4D 较低）和年龄（发育过程中 2D:4D 增加）的关联。然而，我们没有发现 CAH 和对照之间 2D:4D 差异的证据（完整样本：β = −0.001 (−0.008, 0.006)；女性：β = −0.004 [−0.015, 0.007]；男性：β = 0.001， [−0.008，0.011]）。尽管我们的研究结果并不排除 2D:4D 与 CAH 之间存在微小关联，但他们对 2D:4D 作为行为研究中产前雄激素暴露的生物标志物的有用性提出了质疑。