By Elof Axel Carlson
In 1974 I was a Hill Foundation visiting professor at the University of Minnesota, invited by the History of Science Department to interact with its faculty and students. One faculty member who showed up to my seminar class was Robert Desnick who was interested in medical genetics and he had completed both an M.D. and Ph.D.
Four years later I arranged with Desnick, who was on the faculty of the medical school, to go on rounds with his pediatric fellows so I could learn what human genetics disorders were like (30 percent of the pediatric patients had some medical genetic condition). I also used my time there to study the genetics of retinoblastoma, a cancer of the eye in children that can affect one or both eyes, and I published two papers with Desnick on that study. I also met Robert Gorlin who had a dental degree and became a world expert on syndromes of the head and neck and whose book on those conditions was a classic (now in its fifth edition).
I thought about those experiences recently as I read articles in the Public Library of Science (PLoS) on the web about the genetics of the face. All vertebrates have heads with eyes, nose, mouth and ears. I knew from my embryology class as a graduate student that the vertebrate embryo forms a neural tube and one end balloons into a brain. A group of cells along the seamline of the tube migrates and portions of it form the face as do slabs of embryonic tissue that come together to form the skull or cranium. Genes controlling these movements and managing the tissues involved were known from a variety of genetic disorders that Gorlin and Desnick had been following.
In reading the PLoS articles I felt like Rip van Winkle becoming acquainted with a new world that I had slept through. There are now almost a thousand syndromes of human disorders of the head, neck and face. Hundreds of genes involved have been isolated and sequenced. A smaller portion have had their functions worked out. There is one major gene for cleft lip and palate and dozens of other genes that can modify its severity. Some are tied to a vitamin (folic acid) deficiency and may also lead to spina bifida.
The story unfolding at a molecular level is still in its infancy but enough is known to make some reasonable predictions. In a few decades it may be possible to examine the DNA of persons (even mummies or the bones of ancient humans) and reconstruct on a computer screen the portraits of their faces as adults. I toyed with this possibility in 1968 in a public lecture I gave at UCLA (50 years go by like a flash when you turn 87). Back then it was all based on speculation.
In 50 years, as the PLoS articles demonstrate, the changes in knowledge are accelerating thanks to the zebrafish (Danio rerio) as a model organism for vertebrate embryology. The zebrafish embryo has transparent cells, so one can look at embryos forming and identify each of the cells involved.
Biologists have known since Darwin’s writing in the 1860s that facial expressions exist among animals, but humans are remarkable in the nuances facial expressions convey — a Mona Lisa smile, a raised eyebrow of skepticism, a pout, a crying child and the contracted muscles of a bigot shouting slurs are only a few of the many ways we read other people’s faces. At present we can only guess how many genes are involved in these facial gestures. A genetic component is involved because identical twins raised apart for many years show remarkable similarity in their facial expressions and mannerisms.
Elof Axel Carlson is a distinguished teaching professor emeritus in the Department of Biochemistry and Cell Biology at Stony Brook University.