Exploratory genotype–phenotype correlations of facial form and asymmetry in unaffected relatives of children with non‐syndromic cleft lip and/or palate

Abstract

Family relatives of children with nonsyndromic cleft lip with or without cleft palate (NSCL/P) who presumably carry a genetic risk yet do not manifest overt oral clefts, often present with distinct facial morphology of unknown genetic etiology. This study investigates distinct facial morphology among unaffected relatives and examines whether candidate genes previously associated with overt NSCL/P and left–right body patterning are correlated with such facial morphology. Cases were unaffected relatives of individuals with NSCL/P (n = 188) and controls (n = 194) were individuals without family history of NSCL/P. Cases and controls were genotyped for 20 SNPs across 13 candidate genes for NSCL/P (PAX7, ABCA4-ARHGAP29, IRF6, MSX1, PITX2, 8q24, FOXE1, TGFB3 and MAFB) and left–right body patterning (LEFTY1, LEFTY2, ISL1 and SNAI1). Facial shape and asymmetry phenotypes were obtained via principal component analyses and Procrustes analysis of variance from 32 coordinate landmarks, digitized on 3D facial images. Case–control comparisons of phenotypes obtained were performed via multivariate regression adjusting for age and gender. Phenotypes that differed significantly (P < 0.05) between cases and controls were regressed on the SNPs one at a time. Cases had significantly (P < 0.05) more profile concavity with upper face retrusion, upturned noses with obtuse nasolabial angles, more protrusive chins, increased lower facial heights, thinner and more retrusive lips and more protrusive foreheads. Furthermore, cases showed significantly more directional asymmetry compared to controls. Several of these phenotypes were significantly associated with genetic variants (P < 0.05). Facial height and width were associated with SNAI1. Midface antero-posterior (AP) projection was associated with LEFTY1. The AP position of the chin was related to SNAI1, IRF6, MSX1 and MAFB. The AP position of the forehead and the width of the mouth were associated with ABCA4–ARHGAP29 and MAFB. Lastly, facial asymmetry was related to LEFTY1, LEFTY2 and SNAI1. This study demonstrates that, genes underlying lip and palate formation and left–right patterning also contribute to facial features characteristic of the NSCL/P spectrum.

Analyzing Fluctuating Asymmetry with Geometric Morphometrics: Concepts, Methods, and Applications

“…A few studies of shape in Drosophila found no significant directional asymmetry of wing shape [115][116][117][118][119] or mixed results [120][121][122][123][124][125][126], although a series of other studies did find it [15,16,54,56,62,77,85,123]. Similarly, one study on human skulls [127] found no directional asymmetry of shape, whereas several others reported directional asymmetry of the skull [47,68,84,86,90,94,109] and soft tissues of the face and ears [38,66,98,104,105,108]. Further non-significant results were reported from mites [128] and wings of Trichogramma egg parasitoids [129]-but both studies reported results only from relatively small subsamples (≤30 specimens per sample) and tiny organisms, raising questions about statistical power and possible artifacts from mounting very small specimens.…”

“…Several studies have mapped quantitative trait loci with effects on fluctuating asymmetry in mouse mandibles [45,107,392], mouse skulls [64], Drosophila wings [77], and human faces [98]. These studies found at least some loci with effects on fluctuating asymmetry, but it is likely that such analyses have limited statistical power with the experimental sizes that are feasible in most cases.…”

“…Also, the asymmetry scores are not in units of Procrustes distance, and therefore are not easily related to other measures of shape variation in the data. The asymmetry measure using Mahalanobis distance is used in an increasing number of studies, comparing levels of fluctuating asymmetry between groups or correlating it with factors that might influence developmental instability, both for structures with matching symmetry [77,124] and with object symmetry [90,98,108,137,253].…”

Fluctuating Asymmetry of Human Populations: A Review

“…Only in families with a history of cleft-lip/palate was asymmetry (pattern discordance) greater than that of the controls. Recently, Miller et al [70] identified three genes associated with facial asymmetry (actually directional asymmetry) in the relatives of nonsyndromic cleft lip with or without cleft palate; these genes are LEFTY1, LEFTY2, and SNAI1.…”

“…Linear measurements, such as deviations of eye, ear, nostril, and cheek horizontal midpoints from the facial mid-line [69] are common, as are two-and three-dimensional imaging [30,70] and landmark methods for shape asymmetry (geometric morphometrics) [28,41]. In addition to linear measurements, landmark methods of geometric morphometrics have recently been used to study shape asymmetry of the dental arch [68].…”