Three-Dimensional Morphometric Analysis of the Craniofacial Complex in the Unaffected Relatives of Individuals with Nonsyndromic Orofacial Clefts

Seth M. Weinberg

PhD Thesis 2007

Numerous studies have described altered patterns of craniofacial form in the unaffected relatives of individuals with nonsyndromic oral clefts. Unfortunately, results from these studies have been highly variable and have failed to provide a reliable method for discriminating at-risk relatives from controls. In the present study, we compared craniofacial shape between a sample of unaffected relatives (33 females; 14 males) from CL/P multiplex families and an equal number of age/sex/ethnicity-matched controls. A total of 16 x,y,z facial landmark coordinates derived from 3D photogrammetry were analyzed via Euclidean Distance Matrix Analysis (EDMA), while 14 additional linear distances from direct anthropometry were analyzed via t-tests. Variables identified as significantly different (p = 0.10 from EDMA; 0.05 from t-tests) were then entered into a two-group discriminant function analysis. All analyses were carried out for each sex separately.

Compared to controls, female unaffected relatives demonstrated increased upper facial width, midface reduction and lateral displacement of the alar cartilage. A single discriminant function was derived (canonical correlation = 0.43; p = 0.01) which correctly classified 70% of female unaffected relatives and 73% of female controls. Male unaffected relatives demonstrated increased upper facial and cranial base width, increased lower facial height and decreased upper facial height. Again, a single discriminant function was derived (canonical correlation = 0.79; p < 0.001) which correctly classified 86% of male unaffected relatives and 93% of male controls. In both males and females, upper facial width contributed most to group discrimination. Based on the discriminant function results, unaffected relatives were classified into risk/liability classes (high risk or low risk) based on the degree of phenotypic divergence from controls. Results suggest that the craniofacial shape differences characterizing unaffected relatives are partly sex-specific and perhaps more pronounced in males .

The pattern of relative-control differences observed in both sexes is in broad agreement with previous findings from both humans and animal models. Although preliminary, these results suggest that a quantitative assessment of the craniofacial phenotype may allow for the identification of at-risk individuals within CL/P multiplex families. Importantly, the identification of such individuals could lead to improvements in recurrence risk estimation and gene mapping.