Developmental changes of facial fluctuating asymmetry: Bayesian geometric morphometric analysis

Abstract

Objectives: Fluctuating asymmetry (FA), i.e., small random deviations from bilateral symmetry, is an ideal measure of developmental stability and has been recommended as an individual’s health certificate. However, evidence that facial FA is associated with health and nutritional status remains equivocal. We aimed to investigate developmental changes of facial FA and to explore its association with various nutritional indicators. Methods: 3D facial surface images (FB00000491.01) and demographic and nutritional indicators of 2454 individuals of European ancestry were obtained from FaceBase project U01DE020078. Body mass index (BMI) was calculated and used to classify participants’ nutritional status according to WHO definition. Spatially-dense facial landmarks were digitized on each 3D image and generalized Procrustes superimposition was performed to derive shape variables. Individual FA scores were then derived from these shape variables. Bayesian linear model was applied to evaluate demographic and nutritional factors influencing facial FA. Results: After removal of participants with incomplete data, 546 participants aged 5-18 years (female: 278; male: 268) and 1786 participants aged 19-40 years were included for analysis. Age was associated with FA in both genders during 5-18 years (female [Posterior mean (95% Credible Interval)]: 1.10×10-4 (3.49×10-5, 1.86×10-4); male: 2.08×10-4 (1.07×10-4, 3.09×10-4)) while no association was found beyond age 18 years. Male height (2.93×10-5 (1.20×10-5, 4.66×10-5)) and weight (2.30×10-5 (3.56×10-6, 4.22×10-5)) were associated with facial FA during age 5-18 years. In females, height (4.21×10-5 (1.52×10-5, 6.89×10-5)) and BMI (-4.97×10-5 (-8.66×10-5, -1.33×10-5)) were associated with facial FA over age 18 years. During age 5-18 years, obese females (-1.17×10-3 (-2.18×10-3, -1.56×10-4)) and overweight (-1.75×10-3 (-2.82×10-3, -6.94×10-4))/obese (-1.49×10-3 (-2.71×10-3, -2.80×10-4)) males had lower facial FA than normal participants. Conclusions: Facial FA keeps accumulating during development at an average rate twice as fast in males as in females. Nutritional condition impacts facial FA at different life stages in females and in males.