Tuesday, February 20, 2018

The Face of Genetic Determinism

A press release from KU Leuven (Katholieke Universiteit de Leuven) begins
Our DNA determines what we look like, including our facial features. [T]he potential applications are obvious. In the future, doctors could use DNA for skull and facial reconstructive surgery, forensic examiners could sketch a perpetrator's face on the basis of DNA retrieved from a crime scene, and historians would be able to reconstruct facial features using DNA from days long gone.
These remarks were inspired by a paper in Nature Genetics on "Genome-wide Mapping of Global-to-local Genetic Effects on Human Facial Shape." Genome-wide association studies are notorious for false-positive associations between phenotype and genotype, but the researchers from four universities have reasons to believe that the associations are real. The abstract to the paper, refers not only to replication in an independent sample of 3-D images of faces and genetic data, but also to indications that the genes are active when faces develop in the womb (in the cranial neural crest cells that help to generate most of the distinctive skeletal structures of the head and face):
In a sample of 2,329 persons of European ancestry, we identified 38 loci, 15 of which replicated in an independent European sample (n = 1,719). Four loci were completely new. For the others, additional support (n = 9) or pleiotropic effects (n = 2) were found in the literature, but the results reported here were further refined. All 15 replicated loci highlighted distinctive patterns of global-to-local genetic effects on facial shape and showed enrichment for active chromatin elements in human cranial neural crest cells, suggesting an early developmental origin of the facial variation captured.
Previous research started with a smaller number of well-defined physical traits, such as the distance between the eyes. But the paper’s lead author, Peter Claes, a postdoctoral researcher in electrical engineering at KU Leuven, said that
Our search doesn't focus on specific traits. My colleagues from Pittsburgh and Penn State each provided a database with 3-D images of faces and the corresponding DNA of these people. Each face was automatically subdivided into smaller modules. Next, we examined whether any locations in the DNA matched these modules. This modular division technique made it possible for the first time to check for an unprecedented number of facial features.
But even if the fifteen associations between a subset of so many "data-driven" facial features and the enormous number of loci across the genome are meaningful, what do they mean for inferring what the face of a person whose DNA is recovered from a crime scene looks like? Although identical twins look very much alike, is the lead line of the reports from the universities’ PR departments that “[o]ur DNA determines what we look like” oversimplified? Another one of the paper’s authors, Mark Shriver, Professor of Anthropology at Penn State, cautioned that
We won't be able to predict a correct and complete face on the basis of DNA tomorrow. We're not even close to knowing all the genes that give shape to our face. Furthermore, our age, environment, and lifestyle have an impact on what our face looks like as well.
Still, Claes is optimistic that the new associations will have practical value in criminal investigations. Seven of the fifteen genes affect the nose, and
A skull doesn't contain any traces of the nose, which only consists of soft tissue and cartilage. Therefore, when forensic scientists want to reconstruct a face on the basis of a skull, the nose is the main obstacle. If the skull also yields DNA, it would become much easier in the future to determine the shape of the nose.
  • Peter Claes, Jasmien Roosenboom, Julie D. White, Tomek Swigut, Dzemila Sero, Jiarui Li, Myoung Keun Lee, Arslan Zaidi, Brooke C. Mattern, Corey Liebowitz, Laurel Pearson, Tomás González, Elizabeth J. Leslie, Jenna C. Carlson, Ekaterina Orlova, Paul Suetens, Dirk Vandermeulen, Eleanor Feingold, Mary L. Marazita, John R. Shaffer, Joanna Wysocka, Mark D. Shriver, Seth M. Weinberg. Genome-wide mapping of global-to-local genetic effects on human facial shape. Nature Genetics, 2018; DOI: 10.1038/s41588-018-0057-4
  • Ilse Frederickx (Katrien Bollen transl.), Fifteen New Genes Identified that Shape Our Face, KU Leuven News, Feb. 19, 2018, https://nieuws.kuleuven.be/en/content/2018/fifteen-new-genes-identified-that-shape-our-face
  • Seth M. Weinberg, Making Faces: Diving into the Complex Genetics of Facial Appearance, INSIDE Life Changing Medicine, Feb. 19, 2018, http://insideupmc.upmc.com/complex-genetics-facial-appearance/ (providing a more complete and clearer explanation of the findings than their context than the press releases and news stories)