Why Do Some People Have Monobrows?

October 15, 2016

While it may take a bottle of hair dye for us to create a flashy weave that rivals the more colorful and garish representatives from the animal kingdom, humans do still display an incredible sum of diversity when it comes to the hair on their heads. From corkscrew locks to poker straight strands, bushy beards to wispy clumps, our hair varies significantly in its appearance and distribution, across and between populations. A new survey is helping to exposed the genetic basis of such difference, uncovering 10 newgenes links with hair traits, including one linked with monobrowsandthe 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 medication targets that allow a person to adjust the colour of their hair or avoid greying, removing the need for dyes. But that’s quite a bit further down the line.”

Described in the publication Nature Communications, the researchers began their investigation by recruiting more than 6,500 males and volunteers from fiveLatin American countries: Brazil, Colombia, Chile, Mexico, and Peru. This cohort was chosen because the individuals represent a mix of European, Native American, and African ancestry and thus indicate both high genetic difference and diversity when it comes to the hair on their heads.

After assessing hair characteristics based on various categories, including coloring, 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 humen, including those involved in male sexuality 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 discover of the study was uncovering a gene for grey hair, called IRF4. While scientists already knew that this gene was involved in determining hair coloring by controlling the synthesis and storage of the pigment melanin, which also ascertains eye and skin color, this is the first survey to connect it with the process of greying. This could open up new research avenues investigating the exact 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 PRSS5 3 that appears to play a functional role in determining hair curliness. After looking at scalp hair follicles for the purposes of 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 techniques have principally 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.”

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