Facial Curvature Detects and Explicates Ethnic Differences in Effects of Prenatal Alcohol Exposure

Abstract

Background: Our objective is to help clinicians detect the facial effects of prenatal alcohol exposure by developing computer-based tools for screening facial form.

Methods: All 415 individuals considered were evaluated by expert dysmorphologists and categorized as (i) healthy control (HC), (ii) fetal alcohol syndrome (FAS), or (iii) heavily prenatally alcohol exposed (HE) but not clinically diagnosable as FAS; 3D facial photographs were used to build models of facial form to support discrimination studies. Surface curvature-based delineations of facial form were introduced.

Results: (i) Facial growth in FAS, HE, and control subgroups is similar in both cohorts. (ii) Cohort consistency of agreement between clinical diagnosis and HC-FAS facial form classification is lower for midline facial regions and higher for nonmidline regions. (iii) Specific HC-FAS differences within and between the cohorts include: for HC, a smoother philtrum in Cape Coloured individuals; for FAS, a smoother philtrum in Caucasians; for control-FAS philtrum difference, greater homogeneity in Caucasians; for control-FAS face difference, greater homogeneity in Cape Coloured individuals. (iv) Curvature changes in facial profile induced by prenatal alcohol exposure are more homogeneous and greater in Cape Coloureds than in Caucasians. (v) The Caucasian HE subset divides into clusters with control-like and FAS-like facial dysmorphism. The Cape Coloured HE subset is similarly divided for nonmidline facial regions but not clearly for midline structures. (vi) The Cape Coloured HE subset with control-like facial dysmorphism shows orbital hypertelorism.

Conclusions: Facial curvature assists the recognition of the effects of prenatal alcohol exposure and helps explain why different facial regions result in inconsistent control-FAS discrimination rates in disparate ethnic groups. Heavy prenatal alcohol exposure can give rise to orbital hypertelorism, supporting a long-standing suggestion that prenatal alcohol exposure at a particular time causes increased separation of the brain hemispheres with a concomitant increase in orbital separation.

Keywords: 3D Face Analysis; Facial Curvature; Facial Dysmorphism; Fetal Alcohol Spectrum Disorders.

Figure 1

Landmark annotations (n=24) and regions of the face analysed (n=8) Mid-line landmarks (n=6): nasion; pronasale; subnasale; upper/lower lip centres; gnathion Paired left-right landmarks (n=9): lower ear attachment; tragion; inner & outer canthion; upper & lower mid-eyelid; alare; cheilion; cupid’s bow. Facial regions (n=8): face, eyes, philtrum, mandible, nose, malar, upper lip vermilion, profile.

Figure 2

Collapsed groove signature graph for the philtrum for all FAS individualsThe greater homogeneity of the Caucasian philtrum groove signatures is well delineated in the individual heat maps and is confirmed quantitatively in the collapsed signature graph by the large sub-cluster of 32 of 35 Caucasian individuals with FAS and the dispersion indices: Caucasian (0.10) and Cape Coloured (0.54).

Figure 3

Facial growth (PCA1) for control, FAS and HE subgroups of each cohort: A) Cape Coloured; B) Caucasian.

Figure 4

A. Box plots for age-ethnicity normalized PCA1 values reflecting overall facial growth B. Comparison of mean classification results in supplementary table ST1 using a simpler visualisation (mean of CM, LDA and SVM) for both cohorts for each facial region considered. Consistency of classification in the two cohorts is lower for mid-line regions (nose, profile, philtrum and lip vermilion) and higher in non-mid-line regions (face, eyes, mandible and malar region).

Figure 5

Shape, normalised curl and groove of the mean philtrum of Caucasian/Cape FAS subsets (deepest red < −1.0 st dev; deepest blue > 1.0 st dev)

Figure 6

Signature graphs for FAS (red circles), HE who are FAS-like (HE-FAS) in displacement facial difference from controls (green squares) and HE who are control-like (HE-HC) in their difference from matched controls (green circles): A) Cape Coloured; B) Caucasian.

Figure 7

Orbital hypertelorism in Cape Coloured HE subgroup with more control-like facial dysmorphism (HE-HC). Signature of average of Cape Coloured HE-HC subgroup normalised against age-ethnicity matched controls (A). Box plots comparing FAS, controls (HC), and subpartitions of HE into HE-FAS and HE-HC for inner canthal separation (B), inter-pupillary distance (C) and outer canthal separation (D)