John Starbuck and Joan Richtsmeier recently published a paper in the American Journal of Physical Anthropology. This paper is based on chapter 2 of John's dissertation research.
Am J Phys Anthropol. 2013 Mar 15. doi: 10.1002/ajpa.22255. [Epub ahead of print]
Trisomy 21 and Facial Developmental Instability
John M. Starbuck,1* Theodore M. Cole III,2 Roger H. Reeves,3 and Joan T. Richtsmeier1,4
1Department of Anthropology, The Pennsylvania State University, University Park, PA 16802
2Department of Basic Medical Science, School of Medicine, University of Missouri-Kansas City, Kansas City, MO 64108
3Department of Physiology and Institute for Genetic Medicine, Johns Hopkins University School of Medicine Baltimore, MD 21205
4Center for Functional Anatomy and Evolution, The Johns Hopkins University School of Medicine, Baltimore, MD 21205
*Department of Orthodontics and Facial Genetics, School of Dentistry, Indiana University, Indianapolis, IN 46202
The most common live-born human aneuploidy is trisomy 21, which causes Down syndrome (DS). Dosage imbalance of genes on chromosome 21 (Hsa21) affects complex gene-regulatory interactions and alters development to produce a wide range of phenotypes, including characteristic facial dysmorphology. Little is known about how trisomy 21 alters craniofacial morphogenesis to create this characteristic appearance. Proponents of the "amplified developmental instability" hypothesis argue that trisomy 21 causes a generalized genetic imbalance that disrupts evolutionarily conserved developmental pathways by decreasing developmental homeostasis and precision throughout development. Based on this model, we test the hypothesis that DS faces exhibit increased developmental instability relative to euploid individuals. Developmental instability was assessed by a statistical analysis of fluctuating asymmetry. We compared the magnitude and patterns of fluctuating asymmetry among siblings using three-dimensional coordinate locations of 20 anatomic landmarks collected from facial surface reconstructions in four age-matched samples ranging from 4 to 12 years: 1) DS individuals (n=55); 2) biological siblings of DS individuals (n=55); 3) and 4) two samples of typically developing individuals (n=55 for each sample), who are euploid siblings and age-matched to the DS individuals and their euploid siblings (samples 1 and 2). Identification in the DS sample of facial prominences exhibiting increased fluctuating asymmetry during facial morphogenesis provides evidence for increased developmental instability in DS faces. We found the highest developmental instability in facial structures derived from the mandibular prominence and lowest in facial regions derived from the frontal prominence.