Pattern baldness
Pattern baldness, also known as androgenetic alopecia, is the most common form of hair loss affecting the scalp, particularly among men. The condition typically begins with the recession of the frontal hairline and progresses to more significant hair loss on the crown of the head. While it predominantly affects men, women may experience hair loss that does not follow the same pattern, making the underlying causes different. Key risk factors include male gender, age, and family history, with genetics playing a major role in early-onset baldness. Research indicates that the androgen receptor gene is closely associated with male pattern baldness, although environmental factors are also under investigation. Diagnosis is usually made through clinical assessment based on the Hamilton-Norwood scale for men, while women do not have a standardized diagnostic scale. Treatment options include medications like minoxidil and newer candidates like 2-deoxy-D-ribose, but no preventive measures are currently established. Understanding the genetic and molecular basis of pattern baldness may lead to more effective treatments in the future.
Pattern baldness
ALSO KNOWN AS:Male pattern baldness; MPB; androgenetic alopecia
DEFINITION: Pattern baldness, or androgenetic alopecia, refers to the most common form of scalp hair loss. Male pattern baldness follows a typical progression that begins with mild frontal hairline recession, developing to more noticeable frontal hair loss and vertex loss. Female hair loss does not typically follow this same pattern and may have a different underlying etiology.
Risk Factors
The three main risk factors for pattern baldness are male gender, age, and family history. Early-onset baldness is almost entirely dependent on genetic predisposition. By middle age, more than half of the male population will have some degree of pattern baldness. By age eighty, more than 80 percent of men will have pattern baldness. The incidence is much lower in females.
Etiology and Genetics
Anecdotally, pattern baldness is often described as being autosomal dominant or X-linked in inheritance. In reality, opulation studies and genetic research suggest that male pattern baldness is a complex, condition. A combination of both genetic predisposition and environmental factors leads to an individual’s risk for baldness.
The environmental factors involved in baldness development are poorly defined and appear to be significantly less influential than genetic factors. Preliminary studies of multiple different environmental exposures and influences have yet to find a significant association to male-pattern baldness.
While genetic predisposition to baldness appears to be the strongest risk factor, researchers are still identifying the genes involved. Pattern baldness is androgen-dependent, and therefore, early investigations into the genetics of baldness relied on the approach, focusing on genes involved in the sex steroid pathway. The 5 alpha-reductase, aromatase, and androgen receptor genes have all been investigated, with only the androgen receptor (AR) gene showing a clear association with pattern baldness.
The androgen receptor gene is approximately 90 kilobases (kb) long and is located on the X chromosome. Mutations in this gene have been associated with other genetic conditions, but research has not found a specific mutation or functional alteration in men with pattern baldness. Different polymorphisms in the AR gene have been investigated but not confirmed. Current research is focusing on the regulatory regions of the gene, splicing variants, or other epigenetic factors in an attempt to identify specific genetic changes involved in baldness predisposition. AR has been postulated to be the primary genetic factor in the development of early-onset pattern baldness, possibly accounting for up to 40 percent of the total genetic risk.
While other genes in the sex-steroid pathway have not shown a significant association to pattern baldness in previous studies, new technologies and considerations warrant further investigation into these candidate genes. Male pattern baldness has been associated with coronary heart disease, disorders of insulin resistance, and prostate cancer. Investigation of genes involved in these conditions may lead to further identification of predisposition genes.
Genome-wide association studies (GWAS) have yielded new susceptibility variants for pattern baldness. A locus on chromosome 20p11 has shown significant association with male-pattern baldness and was identified by this method. This locus appears to have a strong influence on the development of early-onset hair loss and does not show an association to the androgen pathway. Researchers have also identified and are investigating another locus at chromosome 3q26. In discovering more about these loci, additional information about the molecular basis for hair loss will be gained. Ultimately, this may lead to improved treatments and advance the molecular understanding of the complex diseases that have been associated with pattern baldness.
Symptoms
The degree of male-pattern baldness is defined by the Hamilton-Norwood baldness scale, which contains seven distinct categories of hair loss. As baldness progresses, the hair in the affected region becomes shorter, finer, and less pigmented. Ultimately, the hair follicle is incapable of producing a noticeable hair, rendering the area bald.
Screening and Diagnosis
The diagnosis of male-pattern baldness is made by clinical assessment of scalp hair loss. As female scalp hair loss does not typically follow the same pattern as males, the diagnosis cannot be made by the degrees defined by the Hamilton-Norwood baldness scale. Genetic testing for a predisposition to baldness is being developed.
Treatment and Therapy
Current treatments for hair loss mainly involve medications that were originally intended for other uses but found to have hair growth as a side effect. The best-known treatment, minoxidil, was originally prescribed for hypertension. Its mechanism for stimulation of hair growth is unknown, but as with other similar medications, it is not curative. Other medications that inhibit the actions of 5 alpha-reductase have also been effective and are the basis of future studies. Another potential treatment for pattern baldness is the sugar 2-deoxy-D-ribose (2dDR). In a study published in 2024, researchers at the University of Sheffield found that treatment with 2dDR stimulated hair regrowth in mice. These results suggested that the 2dDR could be equally effective in humans, perhaps as much so as minoxidil.
Ideally, a more complete understanding of an individual’s personal predisposition to hair loss and the molecular pathways involved will allow for a more targeted approach to treatment.
Prevention and Outcomes
There are no known preventive measures for male-pattern baldness.
Bibliography
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