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Abstract
Many factors influence human facial morphology, including genetics, age, nutrition, biomechanical forces, and endocrine factors. Moreover, facial features clearly differ between males and females, and these differences are driven primarily by the influence of sex hormones during growth and development. Specific genetic variants are known to influence circulating sex hormone levels in humans, which we hypothesize, in turn, affect facial features. In this study, we investigated the effects of testosterone-related genetic variants on facial morphology. We tested 32 genetic variants across 22 candidate genes related to levels of testosterone, sex hormone-binding globulin (SHGB) and dehydroepiandrosterone sulfate (DHEAS) in three cohorts of healthy individuals for which 3D facial surface images were available (Pittsburgh 3DFN, Penn State and ALSPAC cohorts; total n = 7418). Facial shape was described using a recently developed extension of the dense-surface correspondence approach, in which the 3D facial surface was partitioned into a set of 63 hierarchically organized modules. Each variant was tested against each of the facial surface modules in a multivariate genetic association-testing framework and meta-analyzed. Additionally, the association between these candidate SNPs and five facial ratios was investigated in the Pittsburgh 3DFN cohort. Two significant associations involving intronic variants of SHBG were found: both rs12150660 (p = 1.07E-07) and rs1799941 (p = 6.15E-06) showed an effect on mandible shape. Rs8023580 (an intronic variant of NR2F2-AS1) showed an association with the total and upper facial width to height ratios (p = 9.61E-04 and p = 7.35E-04, respectively). These results indicate that testosterone-related genetic variants affect normal-range facial morphology, and in particular, facial features known to exhibit strong sexual dimorphism in humans.
Highlights
Differences in facial morphology between males and females are well documented, with major shape differences apparent in the jaw, lips, eyes, nose and cheek regions (Toma et al, 2008; Klotz et al, 2010; Claes et al, 2012b; Koudelová et al, 2015)
We investigated the effect of previously identified genetic variants involved in testosterone regulation on normal-range human facial shape in 7418 European individuals belonging to three cohorts with available 3D facial and genomic data
SHBG is a binding globulin secreted by the liver and its major function is to bind and transport circulating sex hormones with a high affinity; transporting them into the circulation and regulating their action by controlling their bioavailability (Coviello et al, 2012; Vandenput and Ohlsson, 2014)
Summary
Differences in facial morphology between males and females are well documented, with major shape differences apparent in the jaw, lips, eyes, nose and cheek regions (Toma et al, 2008; Klotz et al, 2010; Claes et al, 2012b; Koudelová et al, 2015). Facial sexual dimorphism has been described in children (Kesterke et al, 2016; Matthews et al, 2016, 2018), differences become much more pronounced after the onset of puberty. This accelerated dimorphism post-puberty is the result of changes in circulating hormone levels, which regulate the development and differentiation of male and female primary and secondary sex characteristics, such as voice, body shape and facial morphology (Hines, 2011). Other evidence for the influence of testosterone on facial morphology comes from the craniofacial differences in boys with delayed puberty before and after testosterone treatment. Verdonck et al (1999) described an accelerated craniofacial growth after testosterone treatment, especially in total mandibular length, ramus length, and upper and anterior facial height
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