Julia Pastrana (pictured, right), a Mexican-born woman afflicted with CGH, was exhibited in circuses across the United States and Europe during the mid-19th century. She was often described as not only being excessively hairy all over her body and face, but of having a wide nose, enlarged gums, and overall ‘ape-like’ features.Since the Middle Ages, when this condition was first reported, there has been much speculation over the root causes of CGH. Some have argued that CGH is an example of atavism, or an evolutionary ‘throwback’ to a more primitive ancestor. Others have reasoned (incorrectly) that individuals suffering from CGH represented the missing link between apes and humans, and thus further evidence to support Darwin’s theory of evolution.Because CGH tends to run in families, many believed there was a genetic component to the condition. Now, a team of geneticists led by Xue Zhang of the Chinese Academy of Medical Scientists have uncovered the genetic basis for this condition after examining several families with a history of CGH. Their results are described in the June 12 issue of the American Journal of Human Genetics.One of the researchers’ major challenges was simply finding subjects to study; there have been only a handful of confirmed cases over the past few hundred years. Zhang and his team, however, were able to isolate several examples of CGH for study. They examined three Han Chinese families whose members exhibited various degrees of a form of CGH known as congenital general hypertrichosis terminalis (CGHT). This type of CGH usually causes overgrowth of very thick, dark hair on the face and body, enlarged gums and otherwise distorted facial features. It is believed that Julia Pastrana suffered from CGHT.The researchers also examined an unrelated Chinese individual with a severe case of the condition. For the three Chinese families, the authors created a detailed pedigree in order to determine how CGH was passed down from generation to generation. Then, they performed a high-resolution genetic analysis of each individual. They found at least four distinct genes that were likely related to this condition, all on Chromosome 17. The authors believe that mutations in these genes, specifically either insertions or deletions of strands of DNA within them, may be at the root of the condition. In fact, there have been reports of CGH (or at least CGH-related symptoms) among individuals suffering from trisomy 17; when someone inherits three copies of chromosome 17 from his or her parents, rather than the standard two copies.However, there are several different levels of severity of CGHT, as well as other types of CGH, so it is also clear that much more work must be done to tease out the precise molecular mechanisms for why these four genes on a particular stretch of chromosome 17 should be so central to the prevalence of this rare condition.