AOP report: Adverse Outcome Pathway Network for Developmental Androgen Signalling-Inhibition Leading to Short Anogenital Distance in Male Offspring

This report outlines an adverse outcome pathway network (AOPN) linking reduced androgen signalling during the fetal masculinization programming window to shortened anogenital distance (AGD) at birth. In mammals such as mice, rats, and humans, the AGD is approximately twice as long in males as in females, driven by androgen-dependent differentiation of the male phenotype. Impaired androgen signalling during fetal development can lead to a significantly shorter AGD in male offspring, a sexually dimorphic feature widely used in rodent toxicity studies and human epidemiological research to assess exposure to anti-androgenic substances. AGD measurement is an endpoint in several OECD Test Guideline studies for reproductive toxicity. Notably, androgen signalling can be perturbed by various molecular initiating events, and capturing these causal toxicological pathways may facilitate the use of non-animal test data to help inform predictive toxicology by describing the mechanistic knowledge required for hazard and risk assessment of chemicals. The AOPN includes three AOPs all converging on the same adverse outcome of 'reduced AGD' but with distinct upstream pathways. The upstream portion of the AOPN includes more generalized key events (KEs) and key event relationships (KERs) with broad applicability domains, many of which are measurable by well-established in vitro methods. In contrast, the downstream events have a narrower applicability domain, focusing on development of the perineal region and AGD in male offspring. This report provides overall assessments of AOPs 305, 306, and 307, including one new KE (2298) and four new KERs (2127, 3448, 3449, 3349) not previously reported. The overall confidence for all three AOPs are moderate-to-high with few inconsistencies or uncertainties. The taxonomic domain of the AOPN is mammals, with most evidence coming from mouse, rat and human studies. The upstream network capturing the molecular events has broad taxonomic applicability to all mammals and could likely be extended to some other vertebrates.