Table 1.

Literature review of craniofacial heritability – twin studies.

Study sample	Measures and Techniques	Effect	Reference
NUMBER 79 twin pairs (33 MZ, 46 DZ) SEX DISTRIBUTION MZ: 17 male, 16 female DZ: 14 male, 14 female, 18 male-female AGE DISTRIBUTION 9-16 years mean 12.1 years ETHNIC BACKGROUND Belgium	CAPTURING TECHNIQUE 2D lateral cephalograms STATISTICAL ANALYSIS Model-fitting FACIAL PHENOTYPE 23 measures (linear, angular)	RANGE 45.3–91.2% GENETIC DETERMINATION Total anterior facial height (male) Anterior cranial base Nasion horizontal Incisor superior vertical Incisor inferior vertical ENVIRONMENTAL INFLUENCE Saddle angle Gonial angle Relative sagittal position of the mandible and maxilla to the anterior cranial base NOTES h2: vertical > horizontal measures	Carels et al., 2001
NUMBER 26 twin pairs (10 MZ, 16 DZ) SEX DISTRIBUTION MZ: 5 male, 5 female DZ: 3 male, 7 female, 6 male-female AGE DISTRIBUTION 6-42 years Mean 12 years ETHNIC BACKGROUND Mixed ethnicity	CAPTURING TECHNIQUE 3D facial scans STATISTICAL ANALYSIS Intrapair differences (no h2-values) FACIAL PHENOTYPE 18 landmarks 28 measures (linear) Surface measures (curvature)	GENETIC DETERMINATION Nasal height and width Left eye width Intercanthal width NOTES h2: vertical > horizontal measures High h2 for central midfacial structures (triangular area encompassing the nose, orbital rims, intercanthal area)	Naini and Moss, 2004.
NUMBER 20 twin pairs (10 MZ, 10 DZ) SEX DISTRIBUTION MZ: 5 male, 5 female DZ: 3 male, 7 female AGE DISTRIBUTION mean 12 years	CAPTURING TECHNIQUE 3D facial scans STATISTICAL ANALYSIS Surface shape analysis (no h2-values) FACIAL PHENOTYPE Surface measures (curvature)	GENETIC DETERMINATION Brow ridges Nasion Infraorbital margins ENVIRONMENTAL INFLUENCE Chin Cheeks Lips	Moss, 2006
NUMBER 50 twin pairs (25 MZ, 25 DZ) SEX DISTRIBUTION MZ: 13 male, 12 female DZ: 13 male, 12 female AGE DISTRIBUTION 13.4–20.1 years mean 16.4 years ETHNIC BACKGROUND Iran	CAPTURING TECHNIQUE 2D lateral cephalograms STATISTICAL ANALYSIS classical correlation analysis FACIAL PHENOTYPE 33 measures (linear, angular)	RANGE 6–162% GENETIC DETERMINATION Gonial angle Saddle angle Total anterior facial height Lower anterior facial height Relative sagittal position of the mandible Relative sagittal position of the maxilla Anterior cranial base ENVIRONMENTAL INFLUENCE Upper anterior facial height Mandibular body length NOTES h2: vertical > horizontal measures High heritability found in lower third of the face Low heritability for dento-alveolar variables	Amini and Borzabadi-Farahani, 2009
NUMBER 21 twin pairs (10 MZ, 11 DZ) SEX DISTRIBUTION Same-sex twins AGE DISTRIBUTION 5–12 years Mean 9.3 years ETHNIC BACKGROUND United States Caucasian	CAPTURING TECHNIQUE 3D facial scans STATISTICAL ANALYSIS Classical correlation analysis FACIAL PHENOTYPE 13 landmarks 17 measures (PC)	RANGE 90–100% GENETIC DETERMINATION Breadth of orbital and nasal structures Nasal length, breadth and projection Upper lip height and projection NOTES High h2 for central midfacial structures	Weinberg et al., 2013
NUMBER 37 twin pairs (19 MZ, 18 DZ) SEX DISTRIBUTION MZ: 9 male, 10 female DZ: 7 male, 3 female, 8 male-female AGE DISTRIBUTION 15.5 years ETHNIC BACKGROUND United Kingdom (ALSPAC)	CAPTURING TECHNIQUE 3D facial scans STATISTICAL ANALYSIS Shape analysis (no h2-values) FACIAL PHENOTYPE 21 landmarks Surface measures	GENETIC DETERMINATION Supraorbital and infraorbital ridges Forehead, lower lip and nasal bridge (males) Eyes, philtrum and lower part of the cheeks (females) ENVIRONMENTAL INFLUENCE Lower third of the face NOTES High h2 for central midfacial structures	Djordjevic et al., 2013
NUMBER 141 twin pairs (90 MZ, 51 DZ) SEX DISTRIBUTION MZ: 29 male, 61 female DZ: 20 male, 31 female AGE DISTRIBUTION 15.3–39.6 years Mean 21.7 years ETHNIC BACKGROUND Lithuania	CAPTURING TECHNIQUE 2D lateral cephalograms STATISTICAL ANALYSIS Model-fitting FACIAL PHENOTYPE 39 measures (linear, angular)	RANGE 20–84% GENETIC DETERMINATION Incision inferior to nasion–basion distance Sagittal position of the mandible Gonial angle ENVIRONMENTAL INFLUENCE Mandibular body length Ramus width and height NOTES h2: horizontal > vertical measures h2: form (angular) > size (linear) h2: skeletal > dentoalveolar measures High h2 for the ‘polygon of the facial profile similarity’ (area determined by the angles SNB, NSAr, ArGoMe)	Šidlauskas et al., 2016
ETHNIC BACKGROUND United Kingdom (TwinsUK)	CAPTURING TECHNIQUE 3D facial images STATISTICAL ANALYSIS model-fitting FACIAL PHENOTYPE 21 landmarks 210 pairwise distances	RANGE 0–66% GENETIC DETERMINATION nasal region mouth	de Jong et al., 2016.
NUMBER 604 twin pairs (263 MZ, 341 DZ) 172 unpaired twins (75 MZ, 97 DZ) SEX DISTRIBUTION Female twins	CAPTURING TECHNIQUE 3D facial images STATISTICAL ANALYSIS Classical correlation analysis	RANGE Facial form (uPC): 38.8–78.5% Facial shape (sPC): 30.5–84.8%	Djordjevic et al., 2016
AGE DISTRIBUTION 23.6-86.5 years Mean 58.8 years ETHNIC BACKGROUND United Kingdom (TwinsUK)	FACIAL PHENOTYPE 51 landmarks 1317 measures (linear, scaled PCs, unscaled PCs)	GENETIC DETERMINATION Lips prominence Inter-ocular distance Facial size (height) Nasal width, prominence & height ENVIRONMENTAL INFLUENCE Mandibular ramus height Horizontal facial asymmetry
NUMBER 476 twin pairs (197 MZ, 279 DZ) SEX DISTRIBUTION Female twins AGE DISTRIBUTION Mean 59.3 years ETHNIC BACKGROUND United Kingdom (TwinsUK)	CAPTURING TECHNIQUE 3D facial images STATISTICAL ANALYSIS Model-fitting FACIAL PHENOTYPE 4,096 landmarks 20 distances (Euclidean, Geodesic) 16,384 surface measures (curvature)	RANGE 0–78.9% GENETIC DETERMINATION Chin Nasal region Nasolabial folds Nasion Upper lips Zygomatic bones Inner canthi ENVIRONMENTAL INFLUENCE Orbits Lips	Tsagkrasoulis et al., 2017
NUMBER 1,567 individuals SEX DISTRIBUTION female twins AGE DISTRIBUTION mean 59.3 years ETHNIC BACKGROUND United Kingdom (TwinsUK)	CAPTURING TECHNIQUE 3D facial images STATISTICAL ANALYSIS classical correlation analysis FACIAL PHENOTYPE PCs for orbital and profile subregion	RANGE 76.1–81.5% GENETIC DETERMINATION eyes subregion profile subregion	Crouch et al., 2018
NUMBER 200 twin pairs (37 MZ, 163 DZ) ETHNIC BACKGROUND United Kingdom (TwinsUK)	CAPTURING TECHNIQUE 3D facial images STATISTICAL ANALYSIS Model-fitting FACIAL PHENOTYPE 225 measures (coordinates, distances, areas, angles)	RANGE 0–87% GENETIC DETERMINATION Area: (left) corner mouth, (left) alae nasi and (left) outer corner eye Distance: (right) inner corner eye, (left) alae nasi Area: (left) corner mouth, (left) alae nasi & (left) outer corner eye x-coordinate: (left) alae nasi	de Jong et al., 2018
NUMBER 26 twin pairs (13 MZ, 13 DZ) SEX DISTRIBUTION MZ: 7 male, 6 female DZ: 7 male, 6 female AGE DISTRIBUTION Mean 39 years ETHNIC BACKGROUND Korea	CAPTURING TECHNIQUE 2D lateral cephalograms STATISTICAL ANALYSIS Classical correlation analysis FACIAL PHENOTYPE 23 landmarks 47 measures (linear, angular, ratio)	RANGE -131.8–219% GENETIC DETERMINATION Horizontal relationship between maxilla, mandible and anterior cranial base ° Vertical ratios of anterior facial height shape of cranial base Location of occlusal plane within skeletal framework Vertical relationship among cranial base, palatal plane and mandibular plane ° Lower gonial angle Mandibular body length ENVIRONMENTAL INFLUENCE Anterior and posterior facial height Ramus height NOTES h2: horizontal > vertical > mandible > cranial base > dental measures	Kim et al., 2018.

The first column (‘Study sample’) contains information on the study population. The second column (‘Measures and Techniques’) specifies the methodology. The third column (‘Effect’) summarizes the most important findings of the study (see also column 4 ‘Reference’). Heritability was considered to be low if h²< 35% (i.e., ‘environmental influence’) and moderate to high if h² > 35% and h² > 65%, respectively (i.e., ‘genetic determination’). MZ, monozygotic; DZ, dizygotic.