Facial dysmorphologies in genetic disorders: exploring the ancestry component in a Colombian population.

Currently there are more than 10,000 rare diseases that affect about 7% of the world's population. Up to 40% of rare genetic disorders present craniofacial dysmorphologies, which can vary from subtle facial anomalies to severe malformations. Visual assessment of facial dysmorphology is commonly used for clinical diagnosis, patient management and treatment monitoring. However, qualitative descriptions are usually vague and quantitative approaches using craniofacial phenotypes for the diagnosis of rare diseases are based on North American and European populations, disregarding the influence of population ancestry on facial variation, as in Latin-America. In this study, we assessed facial dysmorphologies associated to three different genetic disorders (Down (DS), Morquio (MS) and Noonan syndrome (NS)) in a Latin-American population from Cali (Colombia). We recorded the coordinates of 18 facial landmarks in 2D images from 34 pediatric patients (19 DS, 8 MS, 6 NS) and 75 controls and quantified facial differences between patients and control groups using Euclidean Distance Matrix Analysis (EDMA). Comparisons between control and syndromic phenotypes indicated that individuals diagnosed with DS and MS presented the largest percentage of dysmorphologies, with respectively 56.2% and 54.9% of significantly different facial traits. In NS, the percentage decreased to 12.4%. Each syndrome presented a characteristic facial pattern. In DS, all facial structures were affected, with a 6% increase of relative distance between the eyes and a 7-10% reduction in facial height. The eyes and nose were most affected in MS, but not the mouth, with higher hypertelorism and facial reduction than in DS (9% and 8-17%). In NS, facial differences were more subtle and affected mainly the eyes and mouth, reducing the relative distance between them from 1 to 4% in patients as compared to controls. Our study provides a precise quantitative comparison of facial dysmorphologies in three genetic disorders that in the future can be compared with other world-wide populations to test whether facial traits associated to disease are altered by different evolutionary and adaptive histories of human populations.