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GENE MAPPING: IT'S ALL IN THE FAMILY
NEW YORK, NY (October 28, 1998) - Gene mapping is a powerful technique used in modern molecular genetics to identify an unknown gene in a family with a particular inherited disorder.
In dermatology, gene mapping has been used to map several inherited disorders in recent years, including different forms of epidermolysis bullas (blistering diseases), ichthyoses (scaling diseases), keratodermas, Darier's disease, Hailey-Hailey disease and PXE, among others. While it has traditionally been used only to map genes in families with rare disorders, more recent advances have made it possible to map genes for more common conditions, such as psoriasis or contact dermatitis, in the future.
Speaking today at the American Academy of Dermatology's Derm Update '98, Angela M. Christiano, Ph.D., Assistant Professor, Departments of Dermatology and Genetics and Development, Columbia University, New York, NY, discussed the hair loss gene, which she discovered through the gene mapping technique.
Gene mapping, also known as "genetic linkage," allows researchers to look for new genes in families where several members are affected with a particular skin disease. Using genetic markers as "signposts," researchers compare about 400 signposts within families and look for locations where all affected individuals carry the same signposts.
The locations are given a score called a LOD score, and if the score is greater than three, then it is known that this association did not happen by chance and, more importantly, that this is where the gene will reside. The challenge then is to look in that region of the chromosome indicated by the mapped signpost and identify the exact gene, and then a mutation, that is responsible for the disease in a given family.
Researchers have isolated a gene involved in some forms of human hair loss. This breakthrough may offer insight into how hair growth is controlled and eventually may offer treatments for those suffering from hair loss and baldness.
The human hair follicle is a dynamic structure that generates hair through a complex, regulated cycle of growth and remodeling. For reasons unknown, a large percentage of the population will suffer from some form of hair loss. There are several forms of hereditary human hair loss, known collectively as alopecias. Some present themselves as male pattern baldness, which is believed to affect
50 percent of the population. Others such as alopecia areata affect three million Americans and cause round, patchy hair loss of the scalp.
Dr. Christiano discussed the applications of gene mapping to inherited hair loss disorders commonly seen in dermatology. For example, the researchers at Columbia recently cloned a gene associated with an inherited form of human congenital alopecia, known as generalized atrichia. Affected individuals are born with infant hair that falls out and never grows back.
These researchers mapped the disease to chromosome 8p21 in humans and subsequently cloned a gene called hairless, responsible for hairlessness in mice. The gene is promising because it acts indirectly by turning on several other genes involved in hair regulation. The research team is trying to identify these other genes, which could be important in more common types of baldness. "Hairless appears to have a multitude of functions, and its role in turning on and off other gene events, such as cell death, is currently under intense investigation," Dr. Christiano said.
A more extensive form of gene mapping, known as complex trait mapping studies, is currently underway. It is anticipated that the hairless discovery will lead dermatology researchers to a better understanding of the genetic control of the hair cycle as the work unfolds. "As opposed to popular hair loss 'treatments,' gene therapy is thought of as closer to a 'cure.' It is an attempt to provide a fix at the base of the problem-at the genetic level," said Dr. Christiano.
The American Academy of Dermatology is the largest medical society representing physicians who specialize in treating conditions of the skin, hair and nails.
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REFERENCE NOTE:
Christiano, A.M.; et al.; Alopecia Universalis Associated with a Mutation in the Human hairless Gene, Science, January 30, 1998, pp. 720-724.
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