Heritability of Face Shape in Twins: A Preliminary Study using 3D Stereophotogrammetry and Geometric Morphometrics

Abstract

Introduction: Previous research suggests that aspects of facial surface morphology are heritable. Traditionally, heritability studies have used a limited set of linear distances to quantify facial morphology and often employ statistical methods poorly designed to deal with biological shape. In this preliminary report, we use a combination of 3D photogrammetry and landmark-based morphometrics to explore which aspects of face shape show the strongest evidence of heritability in a sample of twins.

Methods: 3D surface images were obtained from 21 twin pairs (10 monozygotic, 11 same-sex dizygotic). Thirteen 3D landmarks were collected from each facial surface and their coordinates subjected to geometric morphometric analysis. This involved superimposing the individual landmark configurations and then subjecting the resulting shape coordinates to a principal components analysis. The resulting PC scores were then used to calculate rough narrow-sense heritability estimates.

Results: Three principal components displayed evidence of moderate to high heritability and were associated with variation in the breadth of orbital and nasal structures, upper lip height and projection, and the vertical and forward projection of the root of the nose due to variation in the position of nasion.

Conclusions: Aspects of facial shape, primarily related to variation in length and breadth of central midfacial structures, were shown to demonstrate evidence of strong heritability. An improved understanding of which facial features are under strong genetic control is an important step in the identification of specific genes that underlie normal facial variation.

Keywords: 3D stereophotogrammetry; face shape; geometric morphometrics; heritability; twins.

Fig 1

3D facial surface showing the midfacial landmarks used in the present study. Midline points: n = nasion, prn = pronasale, sn = subnasale. Bilateral points: en = endocanthion, al = alare, sbal = subalare, cph = crista philtri, ch = chelion.

Fig 2

Facial surface warps modeling the shape variation associated with PC4 (along the horizontal axis) and PC5 (along the vertical axis). The centrally located face represents the average or consensus facial surface for the sample. Movement along the principal axes of shape variation in either direction away from the consensus face is accompanied by the 3D displacement of landmarks and modeled as a deformation of the consensus 3D surface. This deformation reflects the major modes of shape variation associated with PC4 and PC5, respectively.