Directional and Fluctuating decomposition and analysis of 3D Facial Discorantie: insights into disordered growth.

The highly variable human face is a biological billboard advertising our sex, ancestry, general health, kinship, genotype and environmental exposures. Large-scale high-dimensional phenotyping of the human face thus offers unique opportunities to unravel basic biological questions in combination with powerful genetic investigations. Emerging technologies of 3-dimensional (3D) scanning and morphometrics (the analysis of form and form variation) are providing the means to establish objective criteria that can be used for phenotypic investigations. Given a population of interest, an individuals facial form (a concept encompassing size and shape independent from orientation, position and scale) is concordant with that population if it is within the boundaries of variation of the population. Stated differently, a concordant shape is in harmony with the population. Shape discordancy, on the other hand, is the lack of harmony. Biologically, this is manifested as the type of facial abnormalities that are best known in craniofacial disorders and dysmorphology. Assessment of such disorders affecting facial morphology is typically performed compared to 'normality'. This, however, presents two major challenges. The first is to define normality or harmony in facial form. The second is to define abnormal variations with respect to normality by identifying and localizing the discordancy in the shape of syndromic faces. The current morphometric approach to this problem is to establish both normal- and abnormal cohorts and to perform an analysis in-between them. This has two major shortcomings: 1) Due to the un-paired setup of the analysis, a proper amount of samples is required to gain enough statistical power. Normal variation can be learned starting from a proper reference dataset consisting of healthy individuals without pathology. The collection of discorded population data however often proves to be more difficult and impractical particularly when dealing with rare and highly variable situations. 2) The current approach loses the power to individualize and can only visualize population differences expressed as a difference between averages or a directional difference. Fluctuating variation (defined as the variation centered on the directional difference) of facial discordancy cohort cannot be measured, which severely limits investigations into disordered growth and development. The only dataset overcoming these shortcomings consists of identical twins, where one of the twins is unaffected whilst the other presents a craniofacial disorder. In such a setup, the unaffected twin serves as a normal-equivalent for the affected twin. Given an un-paired normal and abnormal population, the aim of this project is to create a normal-equivalent for each abnormal observation. This will gain the power to individualize and decompose 3D facial variations into variations of interest. Furthermore, subsequent investigations are based on a paired setup increasing the statistical power even with limited observations. This is an innovative approach to deal with un-paired population based investigations and will reveal innovative content. Furthermore, it can be used in clinical practice as evidence-based as well as patient-specific decision-making.

Keywords:3D Facial analysis, (dys)morphometrics

Disciplines:Metallurgical engineering