Health and Medicine

Why Do Some People Have Monobrows?

March 1, 2016 | by Justine Alford

Photo credit: Check out dem brows. se media/Shutterstock

While it may take a bottle of hair dye for us to create a flashy weave that rivals the more colorful and garish members of the animal kingdom, humans do still display an incredible amount of diversity when it comes to the hair on their heads. From corkscrew locks to poker straight strands, bushy beards to wispy tufts, our hair varies significantly in its appearance and distribution, across and between populations. A new study is helping to reveal the genetic basis of such variation, uncovering 10 new genes associated with hair traits, including one linked with monobrows and the first ever identified for grey hair, called IRF4.

"Now we have a starting point, we want to find what other genes work in tandem with IRF4," lead author Dr. Kaustubh Adhikari from University College London told IFLScience. "Once we have a better idea of this pathway, we may discover potential drug targets that allow a person to adjust the color of their hair or prevent greying, removing the need for dyes. But that's quite a bit further down the line."

Described in the journal Nature Communications, the researchers began their investigation by recruiting more than 6,500 male and female volunteers from five Latin American countries: Brazil, Colombia, Chile, Mexico, and Peru. This cohort was chosen because the individuals represent a mixture of European, Native American, and African ancestry and thus show both high genetic variation and diversity when it comes to the hair on their heads.  

After assessing hair characteristics based on various categories, including color, balding, beard thickness, and the presence of a monobrow, the team then scoured their DNA to look for genes that could be linked with these traits. This kind of investigation is called a “genome-wide association study.”

This led the team to a total of 18 associated genes, 10 of which were new to science. While several genes have already been linked with baldness in men, including those involved in male sex hormone (androgen) signaling, the team uncovered previously unknown genetic links that could possibly represent new targets for the treatment of hair loss.

A summary of the main genes identified and the traits they are associated with. Credit: Kaustubh Adhikari, Emiliano Bellini and Andres Ruiz-Linares.

Perhaps the most notable find of the study was revealing a gene for grey hair, called IRF4. While scientists already knew that this gene was involved in determining hair color by controlling the synthesis and storage of the pigment melanin, which also determines eye and skin color, this is the first study to link it with the process of greying. This could open up new research avenues investigating the precise role of this gene, potentially leading to new cosmetic anti-aging strategies.

Other interesting discoveries include single genes linked with beard bushiness and the prevalence of a monobrow, alongside a gene called PRSS53 that appears to play a functional role in determining hair curliness. After looking at scalp hair follicles under the microscope, they found that the product of this gene, an enzyme, was expressed in a protective layer called the inner root sheath, which creates a passage for the growing strand of hair. Variation in this gene alters the shape of the growing hair fiber, and appears to be linked with straight hair in East Asians and Native Americans.

Alongside the more obvious cosmetic applications of this research, the team thinks that it could be valuable in terms of forensics. For instance, the presence or absence of certain genes in crime scene DNA samples could help build visual profiles and reconstructions of suspects. 

"Forensic methods have primarily been developed in European populations," Adhikari told IFLScience. "Now that we have these new genes found in Latin Americans, we have additional power to do forensic profiling, in which we can predict with a certain degree of accuracy as to whether a suspect has, say, a monobrow, or a particular hair color."

Photo Gallery

Tags