What Is Male Patterned Baldness?
Male patterned baldness, also known in medical terminology as “androgenetic alopecia,” is one of the most prevalent types of hair loss in males. In affected males, hair loss takes place in a specific and defined pattern, starting above the two temples. With time, the patient’s hairline recedes and forms a typical “M” pattern. There is hair loss at the top of the crown also and in most cases the progression to total baldness is a medical certainty.
Male patterned baldness has been associated with many other medical problems like development of coronary heart disease and the enlargement of the prostate gland. Furthermore, an increased risk of prostate cancer, diabetes, obesity and development of hypertension have been associated with male patterned baldness. This condition is prevalent in approximately 35 million men in the USA. It may commence in the teens and the risk becomes higher with increasing with age. It is therefore important to understand the genetics of male patterned baldness.
Genetics of Male Patterned Baldness
Several research studies conducted on the genetic inheritance of male patterned baldness demonstrate that this condition is androgen dependent. This disorder is hereditary and generally follows the genetic inheritance pattern of an autosomal dominant trait. Defects in the AR gene are associated with development of male patterned baldness. Mutations of the AR gene are related with higher risk having of patterned baldness in males. The mutations or changes in the AR gene are caused by tiny variations in the number base pairs which up the gene. Such genetic alterations are common in males who start to have hair loss in their early teens. Research has shown that mutations of the AR gene are responsible for higher numbers of activated androgen receptors on the scalp. It has been established that male patterned baldness is associated with the impact androgens have on the rate of hair growth, but there is still not much information available on why alteration in the AR gene creates a higher risk of patterned hair loss in men who develop this condition.
Several genetic factors seem to play a major part in causing this disorder in males. Research has indicated that in this type of hair loss, the hormones known as androgens especially dihydrotestosterone are very vital for normal sexual development in men both in the fetus stage as well as during puberty. Androgens have the important function of controlling both hair growth and sex drive in men. The AR gene is responsible for initiating the formation of a protein known as the androgen receptor. Androgen receptors enable the human body to respond correctly to hormones like dihydrotestosterone and other androgens. Many studies on male patterned baldness genetic associations have shown that changes in the AR gene cause corresponding increases in the activity of androgen receptors located within hair follicles. It is still not known for sure how these genetic mutations actually help in development of patterned hair loss in men. It has been proposed that other genes may have a role to play in this disorder, but the AR gene’s involvement has been scientifically proven in men suffering from this condition.
Inheritance of male patterned baldness
The genetic inheritance of male patterned baldness pattern is not known since many genetic as well as environmental factors are linked with it. Linkage evidence for an autosomal locus located on 3q26 (AGA1) has been identified for genetic inheritance of this condition (Hillmer et al, 2008.) In males the genetic inheritance pattern for this disorder is believed to be autosomal dominant. If this disorder is said to have an autosomal dominant inheritance, it means that a male just has to inherit one defective AR gene from one parent in order for him to genetically inherit this disease.
Also, male patterned baldness genetic studies indicate that this disorder tends to cluster in families, so if a man has any close relative who suffers from this condition, then his genetic health risk factor for developing it is increased. The genetic transmission when carried down over several successive generations indicates the expression of just a single major gene which has so far been identified as the AR gene. Researchers have found that mutations caused by just one base change in the 5-prime promoter region of the CYP17 gene (609300) seems to modify the inheritance of the disorder in some families, but the mutation in this gene has been effectively excluded as the main or primary genetic defect which transmits this problem. Research is still being done to determine male patterned baldness genetic inheritance patterns and the involvement of other genes in the development of this condition.
1) ‘Androgenetic alopecia.’ (2010). Retrieved on March 18th, 2011 from Genetics Home Reference, A service of the U.S. National Library of Medicine: https://ghr.nlm.nih.gov/condition/androgenetic-alopecia
2) Hillmer, A et al. (2008). Genome-wide scan and fine-mapping linkage study of androgenetic alopecia reveals a locus on chromosome 3q26. American Journal of Human. Genetics, 82: 737-743.
3) ‘MIM ID %109200 ALOPECIA, ANDROGENETIC, 1; AGA1.’ (2010). Retrieved on March 18th, 2011 from OMIM (Online Medelian Inheritance in Man), NCBI (National Center for Biotechnology Information, U.S. National Library of Medicine): https://www.ncbi.nlm.nih.gov/omim/109200