Researchers Home In on Gene That May Cause ‘Werewolf’ Disorder : Science: They say excessive hair growth dates from humanity’s animal ancestors. The trait, though suppressed by evolution, is believed to endure.
Scientists are close to identifying a hair-growth gene responsible for an extremely rare disease that is probably the source of ancient werewolf legends, a finding that serves as a dramatic reminder of humans’ evolutionary proximity to their animal predecessors.
The disease, called congenital generalized hypertrichosis, is characterized by excessive amounts of hair on the face and upper body. When the hair is shaved off, however, victims appear normal, thereby fostering the belief that werewolves were seemingly normal people who underwent a mysterious metamorphosis in the light of a full moon.
Verified victims of the disease, who have numbered perhaps 50 since the Middle Ages, have often worked in circuses as “ape men,” “wolf men” or “human werewolves.”
Although identification of the gene may have little practical value for victims of the disorder, it may shed much more light on the regulation of hair growth, a subject about which scientists know surprisingly little. That, in turn, could eventually lead to new treatments for baldness.
Once scientists learn “what the gene is and how it works, we will have gone a long way toward understanding the causes of baldness in people,” said developmental biologist Gail Martin of UC San Francisco. “That has tremendous psychological and commercial value. Hair growth is very important to people.”
Members of an international team headed by molecular geneticist Pragna I. Patel of the Baylor College of Medicine in Houston report today in the journal Nature Genetics that they have narrowed the location of the gene to a small region of the X chromosome, one of the two sex-determining chromosomes.
Their search for the precise location is proceeding slowly, however, because they have not been able to identify enough victims of the disorder to use conventional gene identification techniques. All of their studies have been conducted on one Mexican family that has 18 affected members.
The excessive hair growth caused by the disorder is probably a typical example of what scientists term an atavistic genetic defect--a mutation that unleashes a gene that has been suppressed during evolution. Human ancestors were once covered with hair from head to foot.
During the course of evolution, they did not actually lose the gene that produced the excessive hair, researchers believe. Instead, the normal activity of that gene was curtailed. The defect in the Mexican family simply allows that gene to function once again.
Other examples of atavistic defects include the occasional third nipple displayed by some humans, the occasional extra digit on the feet of horses and the occasional appearance of hind limbs on modern whales.
These atavisms serve as reminders that genetic characteristics do not get lost during evolution, but simply become latent, awaiting the opportunity to re-emerge, molecular biologist Brian Hall of Dalhousie University in Halifax, Canada, notes in the same journal.
“Atavisms--long an embarrassment to evolutionary biologists--are now seen as potent evidence of how much genetic potential is retained,” he wrote. “The loss of even such complex structures as legs [in snakes] and tails [in humans] does not necessarily mean that the ability to make these structures has also been lost.”
The hypertrichosis disorder was identified in the Mexican family and named in 1984 by Jose Maria Cantu and his colleagues at the University of Guadalajara, a team that has identified more than 40 rare genetic syndromes. Many of those syndromes also have excessive hair growth, but it usually accompanies other genetic problems.
By studying its pattern of inheritance, they were able to determine that the hair growth is a so-called X-linked dominant trait. Males pass the gene on only to daughters, while females pass it on to both daughters and sons. Furthermore, the pattern of hair growth in females is very patchy, a characteristic normally associated with X-linked defects.
The team used conventional techniques to narrow their search to a small region of the X chromosome, but that region still contains many genes. They are stymied now because those same techniques require identification of other families with the disorder to further narrow the search, and they have not yet found other families.
“Defects in hair growth genes are extraordinarily rare,” Martin said. The best hope, Patel concluded, lies in the efforts of the Human Genome Project to identify all the genes on the X chromosome. Once that is accomplished, her team can look at each of those genes and determine which ones are involved in hair growth.
